RU2790423C2 - Copper electrorefining improvement - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: group of inventions relates to a method for the production of electrorefined copper by electrolysis and to a molten liquid metal composition for casting anodes to implement the specified method. Metal copper electrorefining is carried out in an electrolytic cell with at least one copper anode for at least one copper cathode, using an electrolyte based on sulfuric acid. The anode contains the most of 98.0 wt.% of copper and less than 1.00 wt.% of iron. During electrorefining, the electrolyte is removed from the electrolytic cell with an average electrolyte regeneration speed of at least 30% and at most of 1900% per hour. Gas is introduced into the electrolytic cell, and gas is sparged through the electrolyte in an interval between the anode and the cathode.

EFFECT: reduction in requirements for the quality of source raw materials at previous pyrometallurgical stages to obtain purified copper for its electrorefining, while saving advantages of electrorefining with long cycles of anode replacement, high performance, and low energy consumption.

17 cl, 1 dwg, 7 tbl, 1 ex

Description

FIELD OF THE INVENTION

The present invention relates to the production of copper from primary sources, meaning fresh ore, and from recycled materials, also known as recycled materials, or combinations thereof, through pyrometallurgical process steps. Recyclable materials can be, for example, by-products, waste and used materials. More specifically, the present invention relates to the further refining by electrolytic refining of anodes formed from a pyrometallurgical copper stream which contains impurities.

BACKGROUND OF THE INVENTION

In the pyrometallurgical production of copper, other metals such as nickel, antimony, bismuth, tin and/or lead, as well as often small amounts of precious metals (PM), in particular silver (Ag), are present in many raw materials of commercial interest, including both primary and secondary raw materials.

Pyrometallurgical process steps are not capable of economically purifying a copper product stream to the high purity ≥99.97 wt.% that is commonly required in the markets today, for example, the purity ≥99.995 wt.%, which is necessary for drawing very thin copper wire for electronic devices . The copper metal manufacturing process therefore typically includes an electrorefining step, usually as the last step in the refining process.

In the electrorefining of copper using a difference in electrical potentials, copper is dissolved (mainly by electrochemical "corrosion") from a less pure copper anode, usually containing about 99 wt.% Cu, into the electrolyte (mainly in accordance with the reaction Cu → Cu ²⁺ + 2e ^- ) and redeposited on the cathode (mainly in accordance with the reaction Cu ²⁺ + 2e ^- → Cu), forming a copper layer of higher purity (at least 99.97 wt.% Cu and often up to 99.99 wt. .% Cu). The electrolyte is usually a sulfuric acid based electrolyte. These two chemical (half) reactions are characterized by a standard potential difference under ideal conditions of 0.337 V.

By maintaining the potential difference between the anode and cathode within tight limits, the deposition of metal on the cathode can be controlled so that it is almost exclusively copper. Other metals in solution should not precipitate electrochemically.

In theory, since these two chemical half-reactions have opposite potential differences, the electrorefining cell only needs a very small net potential difference to operate. However, due to the varying resistances in the complete circuit, the electrorefining cell in practice requires a potential difference between cathode and anode of at least 0.15 volts (V), or 150 mV, to operate.

Electrorefining (ER) of copper is very different from "electrochemical recovery" (EW) of copper. In electrochemical recovery, the first step is to dissolve the copper in an acidic solution by leaching the copper (strictly chemical "corrosion") from a solid raw material such as copper ore. The copper-containing electrolyte, optionally after increasing the concentration of copper, for example by extraction with an organic solvent, is then passed through an electrolytic cell with chemically inert anodes, in which, due to an electric current, copper is deposited on the cathode. At the anode of the electrochemical extraction cell, water is electrochemically decomposed (2H ₂ O → 4H ⁺ + O ₂ + 4e ^- ), as a result of which hydrogen ions (H ⁺ ) remain in solution, and oxygen atoms collect into gas bubbles that rise to the electrolyte surface. The electrons travel through the electrical circuit from the anode to the cathode, where they become available for copper deposition (mainly according to the Cu ²⁺ + 2e ^- → Cu reaction), similar to what happens in an ER cell. Thus, at EW, these two half-reactions are not inverse to each other, and have different standard potentials, which results in the EW cell requiring an absolute minimum theoretical net potential difference of 0.892 volts. To this theoretical minimum, additional potential differences are then added to overcome the overvoltages at the anode and cathode, as well as the voltage drops associated with the contact points and the ohmic resistance of the electrolyte. Therefore, the operating potential difference between the anode and the cathode in an EW cell is usually much higher than in an ER cell and is in the order of 1.8-2.5 V.

A metal electrorefining cell is typically controlled to maintain a target current (A) or target current density (A/m ² ) for a given cathode surface, primarily to maintain a given cathode mass production rate. However, additional electrical resistances increase during operation, primarily in the electrolyte bath. Since this effect causes, in particular, an increase in electrical resistance at the anode surface, this phenomenon is often referred to as "anodic passivation". Several factors can play a role here: (i) anode sludge that forms and accumulates on the anode surface and impairs the flow of copper cations from the anode to the cathode, (ii) anode erosion, increasing the distance between the electrodes, (iii) electrolyte additives, impairing the flow cations through the electrolyte, and (iv) other mechanisms. Added to this is that higher current densities also accelerate anodic passivation.

Considering the normal operational goal of maintaining a constant current density through the cell, and hence a constant cell performance, the potential difference between cathode and anode is usually (automatically) increased to compensate for any increase in electrical resistance in the cell (I=V/R) .

However, a higher potential difference and/or a higher current density can also create other, less desirable effects in the electrorefining cell, even if they are applied only locally. At voltages that deviate from the optimum, less desirable (electro)chemical reactions may occur, so that some other metals may also begin to deposit on the cathode, resulting in the cathode having a lower purity, and therefore a lower economic value.

Primarily for reasons of cathode purity, the voltage across the copper electrorefining cell is usually maintained within a certain range, typically 0.2-0.6 V, and certainly below a certain maximum, for example, no higher than 1.6 V. The potential difference in the electrochemical recovery cell is significantly higher than in the electrorefining cell, because the potential difference at EW must firstly overcome the standard electrode potential of the copper electrochemical reaction of 0.34 V, and secondly must also provide additional driving force for the electrochemical decomposition of water . Therefore, the potential difference in the EW cell is usually in the range of 1.8-2.5 V.

Also, the current density in electrorefining is usually limited to some upper limit, usually no more than about 400 A/m ² , for the same reason of cathode purity, but also for other aspects of cathode quality such as flatness, strength and toughness, as well as to limit anodic passivation, as previously explained.

Metals nobler than copper and present at much lower concentrations in the anode and/or electrolyte, such as Pb, and also including precious metals such as Ag, Au and platinum group metals (PGMs) such as Pt and Pd , usually go into solution to a small extent. In the context of the present invention, one particular metal may be said to be "more noble" than a reference metal (which in this context is copper) if it has a more positive standard electrode potential (E°), i.e. the minimum voltage required for an electrochemical reaction to occur" Me → Me ^{n +} + ne ^- ". The electromotive force in electrorefining is usually not maintained high enough to "push" the more noble metals present in the anode into solution electrochemically.

Applicants, however, make a distinction between, on the one hand, "electrochemical" dissolution, i.e. going into solution using the electrochemical pathway and therefore consuming electricity, and, on the other hand, purely "chemical" dissolution, i.e. going into solution without any electricity consumption. Metals that can go into solution in this purely chemical way include Sn, As, Sb and Bi.

A number of other metals, including electrochemically "insoluble" metals, can still dissolve by a purely "chemical" mechanism. For example, Pb can dissolve, but in the presence of sulfate anions forms a salt PbSO ₄ which has a very low solubility in the electrolyte and which therefore will tend to fall out of solution and form precipitating Pb compounds.

The copper around these rather "insoluble" metals dissolves, and with the disappearance of copper, these metals remain as loose metal particles floating in the electrolyte, and since they usually have a higher density than liquid, they easily move to the bottom of the cell or lead to the formation a spongy film (eg Pb as PbSO ₄ which is a solid insoluble in the electrolyte) that forms on the anode surface as the surface recedes due to continued copper dissolution.

During electrochemical extraction, copper on the anode does not dissolve. Therefore, the formation of anode sludge and/or a porous film on the anode surface are problems that are hardly known in electrochemical recovery. These problems are typical of electrorefining and essentially only occur in electrorefining.

In prior art electrorefining, it is preferred that anode sludge seeps through the electrolyte and collects at the bottom of the cell as the anodes continue to dissolve, and hence recede, and the cathodes continue to grow. When the anodes are almost used up, all the electrodes can be removed from the bath, the electrolyte above the anode slime can be pumped out, and the bottom of the cell can be cleaned by removing and extracting the anode slime. To minimize the risk of anode sludge particles being trapped in the cathode, forming copper cathode fouling, it is preferable that the anode sludge particles move to the bottom of the cell as quickly as possible by gravity. Therefore, in the field of electrorefining, it is common and preferred to have only a small and slow movement of the electrolyte in the cell. Turbulence in the cell tends to increase the risk that particles or salts of metals other than copper will enter the cathode and contaminate the final product.

The typical copper content of anodes in conventional copper electrorefining is at least 98% by weight. In "The Purification of Copper Refinery Electrolyte", Journal of Metals (JOM), July 2004, pp. 30-33, consultant James E. Hoffmann shows in Table I of his paper the levels of soluble elemental impurities in anode copper, in parts per million ( ^ppm ), for arsenic, antimony, bismuth, iron and nickel, in set of anode compositions known to him. These amounts for individual elements can vary considerably, but the sum of all listed elements together is at most 4545 ^ppm , or 0.45 wt.%. This article also states that anode copper may also contain up to 0.3% oxygen. Assuming that the balance in each composition is copper, it can be concluded that the copper anode compositions disclosed by this author in said article always contain at least 99.2455 wt.% copper, i.e. correspond to the above anode purity formulation for conventional copper electrorefining. This article is about electrolyte management in a copper electrorefining operation. This article briefly discusses alternatives such as liquid extraction and ion exchange, but focuses mainly on the treatment of a continuous effluent from a circulating electrolyte. The article does not touch or give any details about the electrolyte cycle itself and how it should be worked with.

Other documents describe attempts to electrorefine copper using lower purity anodes.

US 2286240 concerns the recovery of metals using electrorefining, starting with a typical anode containing practically 90% copper, 3.5% tin, 5% lead, 0.5% zinc, and the remainder other metals such as antimony, nickel and iron . Anodes having at most 86.0% copper are given as examples. None of the anodes described in this document have any information about oxygen. This document proposes to use an electrolyte containing sulfonic acid as the main electrolytic agent, preferably in the absence of any appreciable amount of sulfuric acid or sulfates, especially when lead is present. This document does not say anything about the removal of anode slimes from the electrolytic cell.

Patent DD 45843 discloses a batch electrorefining operation of copper using an anode containing 90.00 wt.% Cu. A 5 liter supply of electrolyte is at a temperature of 58-59°C and circulates through the cell in such a way that the bath is renewed every 3 hours. Electrorefining is continued until elevated concentrations of nickel sulfate, tin sulfate and/or antimony in the electrolyte make the liquid cloudy. The enriched electrolyte containing 14.63 g/l Ni is then heated to boiling point and treated with an oxidizing agent so that tin and antimony can be removed as a white mud mixture ("Weissschlammenge"), and after the copper removals are evaporated to crystallize nickel as anhydrous nickel sulfate. The anode in DD 45843 contains a large amount of unwanted iron, up to 1.00% Fe. The process according to DD 45843 has the additional disadvantage that anodic impurities can accumulate in the electrolyte over a period and hence the risk of cathode contamination is increased. DD 45843 does not provide information on the quality of the copper cathodes produced.

US 4,351,705 discloses a process for refining copper containing material contaminated with nickel, antimony and/or tin. The first melting furnace produces black copper containing 50-80 wt.% copper. This black copper undergoes a succession of oxidation stages until the residual copper becomes blister, forming converter slag as a by-product. This blister copper is further refined to anode copper containing approximately 98-99 wt % copper, which is cast into anodes which are then processed in the electrorefining stage 10 . Selected portions of converter slag are melted in the second smelting stage 12 at a temperature of about 1200-1300° C. in a moderately reducing atmosphere to obtain a slag residue 114 and batches of fully reduced metal product 13. Fully reduced metal products, which are given as examples and which were cast in the anodes, with the exception of the products of Example 3, to which additional cobalt and nickel were added before casting, contained 63.9-82.10 wt.% copper and at least 10.50 wt.% nickel. In Example 4, the anodes contained 2.0 wt.% iron, and in Example 5 - 0.5% Fe. For the subsequent electrolysis step, these anodes were immersed in an electrolyte in the electrolysis shop taken from a blister copper electrolytic refining section, such as stage 10, or in an electrolyte having a similar content of copper and nickel. In these Examples, the electrolysis cells maintained average current densities of 161 A/m ² and 172 A/m ² . No anodic passivation is reported. Sludges formed during electrolysis both at the anode and at the bottom of the cell. The electrolysis continued up to a maximum of 194 hours (Example 1, 8 days), during which time the total impurity content in the cathode increased to 200 ^ppm , which means that the purity of the cathode fell to 99.98 wt.%. It has been shown that the composition of the electrolyte changes over time, that is, the copper content in it decreases significantly, while the nickel content increases. Sludges on the anodes and on the bottom of the cell were collected in Examples 1 and 3 even separately, presumably at the end of the electrolysis cycle. The electrolysis in US 4,351,705 was performed in relatively short batch cycles that had to be stopped due to sludge buildup, copper depletion and nickel buildup in the electrolyte, and increasing levels of contaminants in the cathodes being produced.

In the field of electrochemical recovery, it is standard to use high circulation of the electrolyte through the cell as well as within it, because this renews the volume concentration of copper in the cell, keeps the stagnant films on the electrodes small, thereby increasing the availability of copper cations on the cathode surfaces and hence improves performance. cells. In addition, in the electrowinning cell, oxygen gas is generated at the anode surface, and the rising bubbles of oxygen gas further improve liquid movement in the cell. It has become fairly common in electrochemical recovery to introduce a gas, usually air, into the bath and to bubble the gas through the electrolyte. This enhances the effect of gas bubbles by increasing turbulence in the electrolyte, and further dilutes the oxygen in the atmosphere above the electrolyte, reducing problems that can be associated with an oxygen rich atmosphere above the electrochemical recovery cell.

Despite the increased risk of cathode contamination, it has been proposed in the art to introduce gas bubbling through the liquid bath also in the electrorefining cell. US 1260830 proposes to introduce gaseous sulfur dioxide and direct it to the surface of the anode. You can also refer to WO 2011/085824 A1 and several documents cited therein. However, neither WO 2011/085824 A1 nor US 4263120 discusses or discloses the increased risk of cathode fouling when air sparging is used as part of the electrorefining operation.

US 3,928,152 and its family members US 3,875,041, US 4,033,839, and US RE30005 disclose air sparging in copper electroplating (EW) at current densities in the range of 59-141 amps per square foot (ASF) of cathode surface, i.e. 635-1517 A/m ² , which are said to be achieved due to the relatively small interelectrode distance, "optimally less than one inch between the front surfaces", while insoluble anodes are provided with convection baffles 18 on their sides and extensions 20 from below, made made of PVC and therefore electrically insulating, combined with additional mixing due to air sparging. Rising air bubbles cause enhanced convection of the electrolyte on the cathode surfaces, preventing sedimentation of suspended particles on the front surfaces of the cathodes. The lower extensions 20 of the anodes extend into the bottom racks 54. Together with the convection baffles 18, these elements maintain a reduced distance of the insoluble anodes from the cathode preforms, the lower edges of which are held in place by their entry into the elements 56 supporting the bubbling tubes. All detailed examples in US 3928152 and other members of his patent family refer to electrochemical recovery. This document suggests that his gas agitation system was carefully tested under electrorefining conditions, with the result that even at current densities up to 300 ASF, anodic passivation did not occur, supposedly completely preventable due to the high convection of the electrolyte, and cathodic deposits were allegedly not contaminated by suspended anode sludge. In US 3928152, as well as in other members of his patent family, there is no information about either the quality of the soluble copper anodes used during these undescribed electrorefining operations, or the rate of electrolyte renewal in the cell. There is also no mention of measures taken to avoid copper depletion in the electrolyte or excessive accumulation of anode sludge. Therefore, it must be concluded that the anodes were of conventional quality and traditionally contained at least 98.5% by weight of copper, making it acceptable to Applicants that no anode passivation was observed despite the high current densities.

Many of the anodic impurities that go into solution, such as Ni, Fe, Co, and Mn, tend to increase the density and viscosity of the electrolyte, which affects the mass and heat transfer mechanisms in the electrolytic cell, such as the movement of copper cations and the rate of deposition of heavy particles. anode sludge to the bottom of the bath. Iron (Fe) in particular is the element that, being in solution, increases the density and viscosity of the electrolyte, thereby increasing the resistance that copper cations must overcome on their way to the cathode, as well as the resistance that anode slimes must overcome on their way to the bottom of the cell.

Since the anodes contain more impurities, the formation of a spongy film on the anode surface can become an increasing factor causing "anodic passivation", that is, the formation of an additional obstacle / resistance that Cu cations must overcome on their way from the anode surface to the cathode surface. To maintain the desired current density through the cell, the cell voltage is increased as anodic passivation becomes more important. The sponge film can also disintegrate into metal particles, which can collect by gravity at the bottom of the electrolytic cell, if they are sufficiently heavy, as part of the so-called anode slimes. Heavy particles of anode sludge can thus form a dust cloud that rises from the bottom of the cell.

Particles to be collected in the anode slime move along the electrodes on their way down to the bottom of the cell and may enter the cathodes as impurities. They disturb the crystal lattice of Cu and can cause uneven growth of the cathode surface and subsequent growth of dendrites, which will lead to a short circuit, and hence to a decrease in performance.

It is clear that a higher level of other metal impurities in copper anodes can exacerbate the problems described above: the anode passivation problem can occur and build up faster, therefore the cell voltage will rise faster, and the level of impurities in the cathode can reach its maximum allowable level faster.

However, a maximum allowable cell voltage may be set, for example due to cathode purity limitations. Other limiting factors may be heat generation in the cell, which can cause thermal distortion and even cracks in the cell walls, and/or melting or failure of parts of the electrical insulation.

Therefore, there remains a need for a method in which these problems can be mitigated. The present invention therefore relates to allowing higher impurity levels in copper anodes, i.e., accepting lower purity copper anodes, resulting in relaxation of upstream process parameters and raw material acceptance criteria, while still producing acceptable quality copper cathodes with acceptable and economically attractive output, while maintaining high cell performance.

C. Anderson et al., "The application of copper metallurgy in the recovery of secondary precious metals", Proceedings of Copper 99 - Cobre 99 International Conference, Volume III - Electrorefining and Electrowinning of Copper, The Minerals , Metals & Materials Society, 1999, pp. 529-543, describes three 1 liter cell electrorefining tests starting with anodes containing less than 75.0 wt% copper and more than 0.8 wt% precious metals (Ag, Au, Pd, Pt). The purpose of this work was to demonstrate the recovery of copper into commercial copper cathodes while recovering all precious metals into anode slimes. It can be assumed that the cell volume of 1 liter refers to the volume of the empty cell before the introduction of electrodes into it. During all tests, a total supply of 3 liters of electrolyte was pumped circulating at a flow rate of 330 ml/minute, or 19.8 liters/hour, through a 1 liter cell and a heated holding vessel. This document does not specify when or where the anode sludge by-product from any of these tests was collected, separated, weighed and analyzed. Considering the cell's high electrolyte renewal rate of 1980% per hour (= 19.8 l/h : 1 l * 100%), it is unlikely that anode sludge could have settled in the cell itself. Some anode sludge may have collected in the holding tank during the test, but it is more likely that the anode sludge was continuously circulated throughout the test along with the electrolyte until at the end of each test the entire supply of electrolyte was drained and/or collected, and the anode sludge could easily settle. Therefore, it is most likely that the anode sludge was recovered only at the end of the electrorefining cycle. These tests used current densities of at most 173.65 A/m ² . The first problem with the electrorefining operation described in this article is that the rate of electrolyte renewal is high, which means that the liquid flow through the cell is also high, which makes it very difficult to maintain the specified distances between the electrodes in the cell and eliminate the risk of a short circuit between adjacent electrodes in their physical contact. The second problem of the described electrorefining operation is the low electric current density, which results in a rather low cell productivity. This document states that no anodic passivation was observed during the last test, which lasted only 3 days at a higher current density of 173.65 A/m ² . This observation of the absence of anodic passivation, despite the high level of impurities present in the anodes, can most likely be explained by the very high refresh rate and low current density used.

The present invention aims to eliminate or at least mitigate the problem described above and/or provide improvements in general.

SUMMARY OF THE INVENTION

According to the invention, there is provided a copper electrorefining process and composition for serving as a copper anode as defined in any one of the appended claims.

In one embodiment, the present invention provides a copper production process comprising electrorefining copper metal in an plating bath from at least one copper anode to at least one copper cathode using a sulfuric acid based electrolyte, characterized in that

- the potential difference between the anode and cathode in the electrolytic cell is maintained at a level of less than 1.6 V,

- the anode contains at most 98.0 wt.% copper,

- the anode contains less than 1.00 wt.% iron,

- the current density through the cell is at least 180 A/m ² of the cathode surface,

the electrolyte is removed from the electrorefining cell during the electrorefining operation at an average electrolyte renewal rate of at least 30% and at most 1900% per hour, and the electrolyte is at least partially removed by overflowing the first electrolyte stream through at least one wall of the cell, and

- introduce gas into the cell and bubbling it through the electrolyte in the gap between the anode and cathode.

In another embodiment, the present invention provides a molten liquid metal composition suitable for making it suitable for electrorefining of copper anodes in the method (process) of the present invention and containing at least 90.10 wt.% and at most 97 wt.% copper, and the rest - other elements as impurities, as part of which this molten liquid metal composition contains

- at least 0.1 wt.% Nickel,

- at least 0.0001 wt.% and less than 1.00 wt.% iron, and

- at least 250 wt. ^ppm and at most 3000 wt. ^ppm oxygen.

The impurities in the metal composition of the present invention are primarily other metals, oxygen, and optionally also sulfur and/or phosphorus. Metals, in the context of the present invention, are primarily meant to be those elements that appear on the June 22, 2007 IUPAC Periodic Table of the Elements to the left of the elements carbon, silicon, selenium, tellurium, and polonium, including those elements themselves. The most common impurities in the metal composition of the present invention are selected from the group consisting of nickel, antimony, tin, lead, bismuth, arsenic, zinc, iron, selenium, tellurium, silver, gold, platinum, palladium, oxygen, sulfur and phosphorus.

Applicants have found that the metal composition of the present invention, preferably after reducing its oxygen content to the level preferred in the context of the present invention, is suitable for casting anodes for the electrorefining process of the present invention, which can be operated with a conventional electrolytic cycle, provided that a number of additional measures have been taken. Applicants have found that the additional measures provided as part of the process of the present invention are sufficient to control problems associated with lower purity and higher impurities in the anode material, for example when the anode is made from the metal composition of the present invention, preferably after reducing its oxygen content, as prescribed.

Applicants have found that keeping the oxygen content within the prescribed upper and lower limits is particularly important if the metal composition of the present invention is produced by a series of pyrometallurgical process steps, in which the last manufacturing step produces a liquid bath consisting of a heavy liquid phase of molten metal found in equilibrium with the floating slag liquid phase, as described in our co-pending patent application PCT/EP2018/084374, filed December 11, 2018. Applicants have found that excess oxygen levels, i.e. above the specified upper limit, contribute to an increase in the copper content in the liquid phase of the molten metallic copper intended for casting anodes, but thereby also lead to the fact that too many other valuable metals end up in the slag phase. In particular, nickel in the presence of excessive amounts of copper and excessively high levels of oxygen tends to oxidize and eventually ends up in the slag phase. This nickel can then be wasted in the final slag of the entire process, generating no profit, and perhaps even causing disposal problems. In addition, most tin, antimony and/or lead will behave similarly under these conditions. Nickel and other metals can be recovered from this slag, but then other ways must be found to remove them from the whole process. Because nickel often behaves very much like copper in metallurgical processes, finding ways to separate nickel from copper is a difficult, if not impossible, task. Applicants have found that with this control of the oxygen level, in particular, nickel can leave the previous metallurgical process as an anode impurity in the process of the present invention.

Applicants have found that controlling the oxygen level in the molten liquid metal composition of the present invention within these limits has the advantage that a significant amount of nickel can be tolerated as part of the molten liquid metal composition of the present invention, whereby the majority of that amount of nickel can be recovered. after the electrolysis step of the process of the present invention and converted into a product of economic value. This has the advantage that the steps of the upstream metallurgical process can take a significant amount of nickel-containing feedstock, i.e., feedstock that is more difficult to process in the conventional copper production process and that typically produces high purity copper as an anode material, such as "blind" copper containing more than 98.0 wt.% Cu.

It has been found that an excessive level of oxygen in the anode increases the risk of anode surfaces not being properly formed upon cooling after casting. Without wishing to be bound by this theory, Applicants believe that the excess presence of oxygen may, in a late stage of solidification, lead to the local formation of gas bubbles below the anode surface, and the pressure in these gas bubbles causes surface distortions that deviate from a perfectly flat surface. These deviations are undesirable from the point of view of the desire to work with small interelectrode distances. Therefore, applicants prefer to comply with the upper limit on oxygen in the anode composition of the process of the present invention.

An excessive oxygen level in the anode also means that more copper is present in the anode in the form of copper(I) oxide, which dissolves chemically in the electrolyte and increases the level of copper in it. The recovery of this copper is typically accomplished with an additional electrochemical recovery step from the drained electrolyte stream, which is complex and represents a significant additional burden. High anode oxygen levels also promote anodic passivation, particularly at high current densities, as described in C. A. Möller et al, "Effect of As, Sb, Bi and Oxygen in Copper Anodes During Electrorefining", Proceedings of Copper 2010 , pp. 1495-1510.

Thus, Applicants have found that for a number of reasons it is advantageous to maintain the oxygen level in the molten liquid metal composition of the present invention within the stated limits, especially in combination with the level of non-copper impurities in the composition, in particular nickel present. One such good reason is that less oxygen in the molten liquid metal composition results in fewer gas pockets in the anodes cast from it. As a result, the anode surfaces become smoother and the anodes flatter, both of which improve the alignment of the anodes in the cell and provide a more uniform spacing between the electrodes in the cell during the electrorefining operation. Applicants have found that it is possible to easily reduce oxygen levels by known means such as teasing to levels preferred by the process of the present invention, thereby converting metal oxides to elemental metal, in particular converting copper oxide to metallic copper, the latter being easily electrochemically dissolves in the electrolyte and is transferred to the cathode in the process of the present invention.

Applicants have found that the molten liquid metal composition of the present invention is the preferred outlet for nickel in prior pyrometallurgical process steps producing the molten liquid metal composition of the present invention. Nickel is quite acceptable in the process of the present invention because it is concentrated in the electrolyte and an overflow stream can be withdrawn from the electrolyte cycle and the nickel contained therein can be selectively recovered and upgraded to elemental nickel.

In "The Purification of Copper Refinery Electrolyte", JOM, July 2004, pp. 30-33, James E. Hoffman describes a number of methods for controlling the composition of the electrolyte in a copper electrorefining operation, primarily by treating such a bleed stream from the electrolyte cycle. Impurities discussed include Sb, Bi, As, Ni, Ca, ammonia, and organic fragments resulting from the hydrolysis of conventional cathode growth modifying additives. As discussed above, the level of impurities in the soluble copper anodes in this article is low, and the purity of the copper in the anodes in this article far exceeds the levels described as part of the present invention.

Applicants have found that the behavior of nickel in the electrolysis cycle is quite unique among the metallic impurities that may be present in significant concentrations in the molten liquid metal composition of the present invention, as well as in the composition of the anode in the process of the present invention. Applicants have found that nickel is able to dissolve in a sulfuric acid electrolyte as nickel sulfate and accumulate to interesting high concentrations before the salt can cause performance problems and/or cathode quality problems. Applicants have also found that the nickel in the electrolyte can be recovered fairly easily from the electrolyte, preferably from a bleed stream that is withdrawn from the electrolyte cycle, and that this nickel can be easily upgraded to commercial value. Applicants have found that the nickel can be recovered and enriched, while most of the copper dissolved in the withdrawn electrolyte can be recovered and enriched, and the acid can be returned to electrorefining.

Applicants have found that this nickel recovery and beneficiation method is the preferred nickel recovery method that is included in the prior pyrometallurgical process for producing the molten liquid metal composition of the present invention and/or in the anode for the process of the present invention.

Allowing for significant levels of nickel in the molten liquid metal composition of the present invention and/or in the anode for the process of the present invention broadens the criteria for accepting feedstock in the prior process of refining copper to form a metal composition. This has the advantage that the upstream process operator can accept larger amounts of high nickel content feedstock, which may therefore be less acceptable or acceptable only in limited quantities to operators of other processes who are not involved in the present process. invention. Therefore, such feedstock may be available at more attractive terms and in more attractive quantities than feedstock containing less nickel.

Applicants have found that higher levels of nickel in the electrolyte resulting from higher levels of nickel in the molten liquid metal composition of the present invention and/or in the anode for the process of the present invention, and thus also in the electrolyte that is withdrawn from the electrolyte cycle for nickel recovery improve the efficiency and effectiveness of the nickel recovery and beneficiation steps because more nickel can be recovered and beneficiated with less equipment and with less energy and/or process chemicals.

Applicants have also found that there is a significant advantage in limiting the iron content of the anodes in this manner. Applicants have found that iron dissolved in the electrolyte leads to a significant reduction in energy efficiency because it causes some of the electrical current passing through the cell not to contribute to the transfer of copper cations from the anode to the cathode. Without wishing to be bound by this theory, Applicants believe that the iron cations in the electrolyte can easily change valence, presumably due to the Fe ²⁺ -> Fe ³⁺ + e ^- half-reaction occurring at the anode, and after the Fe ³⁺ cation has moved to the cathode, the reverse half-reaction Fe ³⁺ + e ^- -> Fe ²⁺ at the cathode occurs, after which the Fe ²⁺ cation can return to the anode. This mechanism may explain the observation that, in the presence of a significant amount of iron in the electrolyte, part of the electric current can pass through the cell without contributing to the transport of copper cations. Therefore, this part of the electric current represents an unproductive use of an expensive resource.

Applicants have also found that due to the presence of iron in the anodes, and thus also in the electrolyte, additional but non-contributing electrical current is needed to maintain the same copper cathode performance, which increases the problems that the present invention solves. This increased current results in an increase in the cell voltage as well as an even faster rise, resulting in higher levels of contaminants in the cathode and faster reaching of the maximum allowable level, as explained earlier in this document. The higher current also creates more heat in the cell, and possibly hot spots, which causes other problems described elsewhere in this document. It also increases the current density for the same copper performance, which increases its contribution to cathode fouling, which will be explained below.

Iron, when it is dissolved from the anode into the electrolyte, increases the density and viscosity of the electrolyte, which affects the mechanisms of mass and heat transfer in the electrolytic cell, for example, the movement of copper cations on their way to the cathode and the rate of settling of heavy particles of anode sludge to the bottom of the bath. A high Fe content in the anode, and thus also in the electrolyte, increases the resistance that copper cations must overcome on their way to the cathode, as well as the resistance that anode slimes must overcome on their way to the bottom of the cell.

It is for this reason that the anodes in the process of the present invention, as well as the molten liquid metal composition of the present invention, must contain iron at a level that is below a predetermined upper limit.

The molten liquid metal composition of the present invention, and preferably also the copper anode in the process of the present invention, optionally contains at least 0.0001 wt% iron, preferably at least 0.0005 wt%, more preferably at least 0 .0010 wt.%, even more preferably at least 0.0025 wt.%, preferably at least 0.0050 wt.%, more preferably at least 0.0075 wt.%, even more preferably at least 0.010 wt. .%, preferably at least 0.015 wt.%, more preferably at least 0.020 wt.%, and even more preferably at least 0.025 wt.% iron. Applicants have found that it is not necessary to remove iron from the anode composition and/or molten liquid metal composition of the present invention to levels below the detection limit of 1 wt. ^ppm (ppm by mass), but it is preferable to leave a small amount of iron. This reduces the constraints, stiffness and workload of the upstream process steps that produce the metal that forms the basis of the anodes in the process of the present invention. Therefore, it should be noted that the lower limit of iron content prescribed for the molten liquid metal composition of the present invention, as well as prescribed for the composition of the copper anode used in the process of the present invention, is not an essential feature of the invention, which would be necessary to obtain the desired result. It has no technical bearing on the technical effects on which the present invention is based. Compliance with the lower limit is preferable because of the associated advantages that appear before the stage of electrorefining.

Applicants state that pyrometallurgical processes that produce liquid molten copper products suitable for casting into electrorefining anodes typically use metallic iron as a reducing agent and/or as an energy source. The presence of a measurable amount of iron in the molten liquid metal composition of the present invention and/or in the anode composition of a process such as this is therefore a useful marker that indicates that the composition and/or anode was produced by a pyrometallurgical process and was not the result of an artificial, usually on a laboratory scale, combining pure copper with other high purity metals to produce an anode having a particularly desirable composition for experimental purposes and highly controlled testing.

Applicants have found that the electrorefining of copper anodes, which contain less copper and therefore contain high levels of impurities, typically other metals, at these high current densities becomes more and more problematic as the level of impurities in the anode increases because the anode contaminants and high current densities interact to exacerbate the problem of anodic passivation. Applicants have found that this problem can be solved by the features of the present invention, in particular in combination with each other.

Applicants have found that introducing a gas and bubbling that gas through the electrolyte between the anode and cathode in the electrorefining operation, preferably from the anode side of the gap, results in improved mixing of the electrolyte. Provided that this gas injection is performed properly, as described later in this document, it achieves this effect locally, in the gap between the electrodes, where its effect is greatest, while it has almost no effect on liquid flows elsewhere in the cell. , for example, at its bottom, where a significant part of the anode slimes is collected. This improved liquid mixing first improves the physical transport of Cu ²⁺ cations from the anode to the cathode by convection. This is achieved by increasing turbulence in the liquid between the electrodes, accelerating the transfer due to convection, and also by reducing the diffusion boundary layer on the surface of the anode and/or cathode, which is stagnant and through which transfer occurs due to diffusion. Another benefit is a more uniform distribution of temperature and process chemical concentrations throughout the cell, which also improves the uniformity of the current distribution. These effects have the advantage of providing high cell performance while allowing the cell to maintain a lower potential difference and obtain a higher purity cathode compared to no or less bath agitation. A lower cell potential difference has the benefit of lower power consumption for the same product yield.

While not wishing to be bound by such a theory, applicants believe that this is due to the physical reduction and mechanical breakdown of the spongy film that continuously forms on the anode surface, as well as improved electrolyte concentration homogenization in terms of levels of copper and/or contaminant metals, temperatures and additives. This reduces the risk of local "hot spots" in the bath with respect to any of these parameters.

Such hot spots can be detrimental in terms of temperature and/or concentrations of copper, metal contaminants and additives. Contaminating metals can locally accumulate and increase the potential difference in the cell, or even locally between one particular pair of electrodes or between different points on the same electrode, and therefore can reduce cell performance as well as cathode quality. The lack of copper at the cathode end can reduce the rate of deposition. Localized hot spots of a soluble metal such as nickel can lead to localized deposition of salts of that metal. Local temperature fluctuations can cause damage to the cell walls and/or insulation paths providing electrical insulation between different parts or elements of the cells. Localized temperature spikes can also accelerate the degradation of certain process chemicals or additives and can even lead to premature "stripping" of the cathode, i.e. premature separation of the cathode copper layer from its substrate already during electrorefining. This premature stripping easily leads to short circuits and loss of production.

Applicants claim that a given upper limit of anode iron content contributes to the benefits discussed here, such as lower voltage, lower power consumption, and lower occurrence of hot spots. Limiting the iron content in the electrolyte increases the current efficiency and improves mass and heat transfer through the electrolyte.

Applicants have found that the feature that determines that the rate of removal of the electrolyte from the electrolytic cell must meet the specified lower limit, further contributes to the increase in the agitation of the bath. This further enhances the benefits described above in connection with the introduction and bubbling of gas through the electrolytic cell.

Applicants have found that high bath electrolyte velocities, caused by a high electrolyte removal rate from the bath and/or additional turbulence caused by bubbling gas through the bath, have surprisingly significant effects as they limit buildup and hence the thickness of any sponge film and/or risk of deposition of sludge particles on the surface of the anode and/or cathode. Applicants have observed that the sponge film is quite brittle and believe that gas bubbles can also mechanically attack the sponge film. Applicants believe that high fluid velocities in the electrolyte also greatly contribute to the destruction of the sponge film on the anode, as well as the removal of suspended particles of anode sludge from the electrodes.

The high rate of electrolyte removal from the bath also limits the accumulation of solid particles in the electrolyte present in the space between the anode and cathode. The high removal rate allows at least a portion of the formed anode sludge particles to be removed from the removed electrolyte before returning the purified electrolyte back to the electrorefining cell as part of the present invention. The features of the present invention have proven to significantly limit the effect of "anodic passivation" as explained elsewhere herein.

The electrolyte that is removed from the electrorefining cell contains suspended particles of anode sludge. While heavy anode sludge particles can still easily sink through the electrolyte, despite the movement of gas bubbles through the electrolyte, lighter anode sludge particles may not settle as easily and are likely to tend to move up to the surface where they are carried away. and are removed from the cell by electrolyte overflow. Thus, a high rate of electrolyte removal also means a high rate of removal of at least a portion of the lighter anode slimes. This benefits from a high rate of removal of anode slimes from the cell. This has the advantage that the total amount of anode sludge that can accumulate in the cell over time remains limited. With frequent or continuous removal of anode slimes, for example by entrainment with the electrolyte being removed, the likelihood of contaminating metals entering the cathodes is reduced. Another advantage of having more frequent access to anode sludge than only at the end of the electrorefining cycle, ie only after the anodes are used up, is that the availability of anode sludge is spread over a wider period of time. This has the advantage that any further anode slime treatment can be spread out more evenly over time, which offers the benefits of smaller equipment and lower investment costs combined with easier operation and planning, even to the extent that anode slime treatment can carried out continuously. An additional benefit is that, due to the significant value that these anode slimes can represent, largely due to the presence of DM, including PGM, improved access to anode slimes reduces the amount of working capital that, on average, can be involved in work in progress. from anode sludge at operating plants.

Applicants have however found that excessively high electrolyte flow through the electrorefining cell can create other problems. Usually the anodes and cathodes in the cell hang freely and strictly vertically under the influence of their own weight, side by side and in an alternating manner at their calculated distance from their nearest neighbors. The physical distance between the surfaces of the anodes and cathodes sets the distance that the cations must pass through the electrolyte. The resistance that this physical flow of cations encounters as it passes through the electrolyte is an important element of the overall electrical resistance in the cell and therefore contributes significantly to the potential difference that is required to overcome the overall electrical resistance and provide the desired current density, and hence cell performance. Physical movement or displacement of the electrodes in the cell can cause the distance between the electrodes to no longer be uniform, resulting in an uneven distribution of current density, a local increase in the cathode growth rate and an unacceptable local level of additives, and hence a reduced quality of the cathode. Adjacent electrodes must also not come into physical contact with each other, because this means an electrical short circuit. A short circuit between the anode and cathode during electrorefining nullifies the electrical potential difference between them, which is the driving force of electrolysis, and therefore stops the electrochemical dissolution of the anode and the deposition of copper on the cathode, and this despite the fact that most of the electricity is converted into local heat dissipation, which may even cause the two electrodes to become firmly connected to each other.

Fluid movement in the cell can push one electrode towards its neighbor and therefore cause the problems described above, including an increased risk of physical contact. This problem is complicated by the fact that the growth of the metal on the cathode can be uneven. Dendrites may be formed which may protrude perpendicular to the cathode surface. Also, irregularities, such as the sponge film described elsewhere herein, can form on the anode surface. Therefore, the distance between the electrodes for which a particular electrolytic cell is designed is usually an acceptable balance between, on the one hand, the desire to reduce the required potential difference in the cell, and, on the other hand, the desire to limit the risk of physical contact between adjacent electrodes, and hence a short short circuits during the duration of a complete electrolytic cycle. The electrodes more prone to movement due to electrolyte movement during electrorefining are in particular the cathodes at the beginning of the electrolytic cycle and/or closest to the electrolyte inlet, as they are the lightest in weight and/or may face higher pressure. fluid flow. Similarly, end-of-cycle anodes, referred to here as spent anodes, also pose a significant risk due to their reduced weight.

It has been proposed in the art, as well as in some of the documents discussed above, to limit the movement of the electrodes in the electrolytic cell by physical means, such as guides at the wall or bottom of the cell, into which the electrodes are placed as they are lowered into the electrolytic cell. However, the problem is that metal growth on the cathode can attach the cathode to the guide or stand so that at the end of the electrolytic cycle it becomes difficult or even impossible to release the cathode from the guides and/or stands in the cell. The problem becomes even more intractable in electrorefining, when fresh anodes are less clean, i.e. when there is more anode sludge and more spongy film that can form on the surface of the anode, and also because of the presence of more contaminant particles that can enter the cathode. . The cathode surface may grow unevenly, and the growth of the cathode may preferentially continue on these protrusions due to the reduced distance from the anode, thereby forming "dendrites" that move further and further away from the rest of the cathode surface. In particular, when the anodes are relatively rich in tin and antimony, Sn/Sb intermetallic compounds and/or oxides can form, which tend to grow strongly on the cell walls and side stripes of the blanks and impair the release of the finished cathode from any joints or clamps provided on the wall or bottom of the cell.

Another problem with providing guides or clamps to restrict movement of the electrode relative to the wall or bottom of the cell is that it prevents heavy anode sludge from being removed from the cell, particularly when it is preferred to do so during an electrolytic cycle. These electrode guides can obstruct the movement of, for example, a suction head to remove sludge from the bottom of the cell. Any physical attachment to the bottom of the cell prevents sludge from being removed from the cell until it is first removed. In turn, the vertical guides of the electrodes along the walls of the cell can interfere with any horizontal wall fixtures that guide the suction head to extract the slurry. Therefore, the possibilities of supplying guide electrodes are limited in combination with the possibility of removing heavy anode slimes during the electrolytic cycle.

Applicants have found that the electrorefining process of the present invention, due to the high content of impurities in the anodes, limits the options for providing guides to restrict movement of the electrodes in the cell. Thus, the purpose of the upper limit that is given to the rate of removal of electrolyte from the cell in the process of the present invention is to limit the movement of the electrodes during operation and therefore the risk of short circuits, while avoiding the need for a significant supply of physical guide electrodes, for example, along the walls of the cell or at the bottom of the cell, so that the extraction of the sludge is not disturbed. Limiting the rate of electrolyte renewal in the cell also saves the capital and operating costs of the equipment and energy required to circulate the electrolyte.

Thus, Applicants have found that electrorefining can be successfully used to produce high quality cathodes, starting from anodes of lower purity, provided that gas is introduced and bubbled through the electrolyte and the flow of electrolyte through the electrolytic cell is high enough to control the concentration of more of light anode sludge in the cell, but still low enough that electrode movement caused by fluid flow pressure remains low and eliminates the need to provide physical guides to restrict electrode movement so that removal of heavy anode sludge from the cell is not impaired.

Thus, the present invention reduces the negative effects on cathode quality that can be caused by increased levels of impurities in copper anodes. As a result, the present invention allows the processing of less pure copper anodes, ie anodes having a significantly higher level of impurities.

Applicants have found that the process of the present invention greatly reduces the purity requirements of the copper stream, which may be suitable for casting into anodes, which can then be refined into commercial high purity copper cathodes via electrorefining. The process of the present invention allows for much higher concentrations of contaminant metals in the anodes compared to the current state of the art. This means that the upstream process by which anodes are produced can be operated with less stringency, such as less stringent quality restrictions, which can benefit from higher productivity.

Applicants have found that the process of the present invention allows these benefits to be obtained without any significant compromise with respect to the recovery of copper into the copper cathode.

Applicants have further found that the process of the present invention allows these benefits to be obtained while limiting the amount of other metals entering the copper cathode to commercially acceptable levels.

Applicants have further found that the process of the present invention provides the option to recover as much as possible of the metallic contaminants in the anode metal, which includes Bi, Sn, Pb, As, and Sb, as well as precious metals such as Ag, Au, Pd, Pt, as part of the anode sludge by-product.

Applicants have further found that the process of the present invention provides an optional opportunity to maximize the recovery of nickel that may be present in the anode metal from the electrolyte.

The advantages of lower anode metal quality requirements are that (a) the prior pyrometallurgical copper recovery steps can use feedstocks of much lower purity and/or that the operating window for refined copper production is extended, suitable for the electrorefining step, and (b) relaxation of compositional restrictions placed on feedstock deemed acceptable for this primary copper recovery by pyrometallurgical stages.

Therefore, the present invention also has the advantage of (a) relaxing the requirements for acceptable feedstock quality in prior pyrometallurgical processing steps so that feedstock that is more heavily contaminated with the listed metals can be processed and therefore can be more readily available under more economically favorable conditions. , and (b) reducing operational problems and costs in upstream pyrometallurgical steps to produce a purified copper stream that is suitable for copper electrorefining from less copper-rich feedstocks.

The present invention has been found to provide these benefits while maintaining the benefits of an electrorefining operation that allows long anode change cycles, high productivity, and high current density and low power consumption to be operated. Applicants have found that the process of the present invention can be provided in such a way that it only needs to be interrupted to replace the anodes, but as will be explained later in this document, the concentration of the electrolyte, as well as the accumulation of anode sludge in the cell and in the electrolyte, can be well controlled. , and even cathodes can be replaced without stopping the electrolysis process.

The present invention achieves this goal by reducing the effect of anodic passivation and the accumulation of contaminants in the electrolyte. Other advantages are also obtained, such as the possible selective recovery of Ni from Cu as well as other metals by means of anode slimes.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a block diagram of the main part of one embodiment of the process of the present invention.

DETAILED DESCRIPTION

The present invention will be described in the following by way of specific embodiments, with possible reference to specific drawings, but the invention is not limited thereto, but only by the claims. The drawings described are only schematic and non-limiting. In the drawings, some of the elements may be exaggerated and not to scale for illustrative purposes. The dimensions and relative dimensions in the drawings do not necessarily correspond to the actual ones.

In addition, the terms "first", "second", "third", etc. in the description and in the claims are used to distinguish between like elements, and not necessarily to describe sequential or chronological order. These terms are interchangeable under appropriate circumstances, and embodiments of the invention may operate in other sequences than those described and/or illustrated here.

In addition, the terms "top", "bottom", "above", "under", etc. in the description and in the claims are used for descriptive purposes and not necessarily to describe relative positions. These terms are interchangeable under appropriate circumstances, and the embodiments of the invention described herein may operate in other orientations than those described or illustrated herein.

The term "comprising" as used in the claims is not to be construed as being limited to those elements listed in context with it. It does not exclude the presence of other elements or steps. It should be considered as characterizing the presence of the claimed features, items, steps or components, but does not preclude the presence or addition of one or more other features, items, steps or components, or groups thereof. Thus, the scope of "an article containing means A and B" cannot be limited to an object that consists solely of means A and B. It only means that A and B are the only elements of interest in the subject matter associated with the present invention. . Accordingly, the terms "comprising" and "including" encompass the more restrictive terms "consisting essentially of" and "consisting of". Therefore, when the phrases "comprising" and "comprising" are replaced by "consisting of", these terms form the basis of preferred but narrowed embodiments, which are also offered as part of the content of this document in relation to the present invention.

Unless explicitly stated otherwise, all values given here include the end points of the specified ranges, and the values of the content of ingredients or components of the compositions are expressed in mass percent, or in wt.% of each ingredient in the composition.

Additionally, each compound used herein may be referred to interchangeably using its chemical formula, chemical name, abbreviation, and so on.

The present invention is directed to the electrorefining of copper, that is, the purification of a copper stream containing impurities, in particular other metals, from which anodes are made, into copper cathodes having a higher copper purity. This differs significantly from the electrochemical extraction of copper. In the hydrometallurgical recovery of copper from ores or other raw materials, metals are leached from the original solid into a liquid leach solution by dissolving the metals with strong acid solutions (such as sulfuric acid or hydrochloric acid). In a subsequent electrochemical recovery step, copper can be recovered from the liquid leach solution or from its concentrate by selectively pushing the copper cations out of the solution and depositing the copper on the cathode under the action of a potential difference between the cathode and a chemically inert anode, usually made of lead, on which surface water is electrochemically decomposes into gaseous oxygen (O ₂ leaving the cell) and protons (H ⁺ ), which remain in solution. For every proton produced, one electron is released. These electrons travel through an electrical circuit from the anode to the cathode and are collected at the cathode to deposit metallic copper (primarily by the Cu ²⁺ + 2e ^- → Cu reaction), similar to what happens at the cathode during electrorefining.

Because electrowinning must also decompose water into oxygen and protons, it has been explained earlier in this document that the theoretically minimum required potential difference in an electrowinning copper cell is significantly higher than that of a copper electrorefining cell. The practical potential difference in the electrochemical copper recovery cell is at least 1.6 V, and in practice a potential difference in the range of 1.6-2.5 V is used to also overcome additional resistances in the electrochemical recovery electrolyte.

In the context of the present invention, the rate of electrolyte renewal in an electrolytic cell refers to the rate of electrolyte removal as a percentage relative to the liquid volume of an empty electrolytic cell per unit of time, typically per hour. By empty electrolytic cell is meant the amount of liquid that the cell can contain when it is still empty, i.e. before the introduction of electrodes, other elements or submersible accessories such as electrode guides and/or suction pipes and/or piping and/or or distributors for incoming and/or outgoing fluids, gas and/or liquid. The renewal rate in the context of the present invention is the renewal rate of an electrolytic cell, more specifically one or more cells belonging to the same electrorefining unit, and is therefore completely independent of the volume of any drain stream, which is usually continuously withdrawn from the circulating electrolyte, which is also can be considered as a "renewal rate", but in relation to the entire electrolyte cycle as a whole, and which has nothing to do with the renewal rate defined in the context of the present invention.

The requirements for the renewal rate in the context of the present invention refer to the average renewal rate over the entire electrolytic cycle, ie the period of operation between two successive anode changes. We will discuss later in this document that more than one electrolyte stream may be removed from a cell and that such removal stream need not be continuous, but may be discontinuous. Therefore, it may happen that during certain periods of operation, the rate of electrolyte removal from the cell may periodically increase significantly. Therefore, the prescription for the average renewal rate in the context of the present invention is the average value throughout the entire electrolytic cycle, including any periods during which the electrolyte removal rate is higher. The time period for the average update rate refers only to the time of operation, that is, to the time when the cell is at least partially in operation with an electric current passing through the cell.

In one embodiment of the present invention, the potential difference between the cathode and the anode in the electrolytic cell is at most 1.5 V, preferably at most 1.4 V, more preferably at most 1.3 V, even more preferably at most 1.2 V, preferably at most 1.1V, more preferably at most 1.0V, even more preferably at most 0.9V, preferably at most 0.88V, more preferably at most 0.85V, even more preferably at most 0 .83V, preferably at most 0.80V, more preferably at most 0.7V, and even more preferably at most 0.6V. the anodes become essentially used up and must be replaced, and the cell voltage is usually the highest. Applicants prefer to keep the cell voltage below a predetermined upper limit because it reduces cathode fouling and improves cathode quality, and in doing so it reduces the risk of cell resistance becoming too high, which can lead to temperature spikes that can cause thermal stresses, additive breakdown, and other unwanted effects.

In one embodiment of the present invention, the anode contains at most 97.5 wt.% copper, preferably at most 97.0 wt.%, more preferably at most 96.5 wt.%, even more preferably at most 96.0 wt.% , preferably at most 95.5 wt.%, more preferably at most 95.0 wt.%, even more preferably at most 94.5 wt.%, preferably at most 94.0 wt.%, more preferably at most 93, 5 wt%, even more preferably at most 93.0 wt%, preferably at most 92.5 wt%, more preferably at most 92.0 wt%, and even more preferably at most 91.5 wt% copper. Applicants have found that some of the benefits of the present invention become even more significant when the anodes are less pure, ie contain more other metals than copper. For example, this expands the acceptable raw material quality requirements for upstream pyrometallurgical process steps, as well as the operating window for upstream pyrometallurgical stages from which anode metal is produced.

In one embodiment of the present invention, the anode and/or molten liquid metal composition of the present invention contains at most 0.90 wt.% iron, preferably at most 0.80 wt.%, more preferably at most 0.70 wt.%, still more preferably at most 0.60 wt%, preferably at most 0.50 wt%, more preferably at most 0.40 wt%, even more preferably at most 0.30 wt%, preferably at most 0.25 wt.%, more preferably at most 0.20 wt.%, even more preferably at most 0.15 wt.%, preferably at most 0.10 wt.%, and even more preferably at most 0.050 wt.% iron. This has the advantage that the electrolyte will also contain less iron and that the problems associated with the presence of iron cations in the electrolyte can be more easily kept low, down to an acceptable level, or even virtually eliminated.

In one embodiment of the present invention, the current density through the cell is at least 190 A/m ² , preferably at least 200 A/m ² , more preferably at least 210 A/m ² , even more preferably at least 220 A/m 2 m ² , preferably at least 230 A/m ² , more preferably at least 240 A/m ² , even more preferably at least 250 A/m ² , preferably at least 260 A/m ² , more preferably at least at least 270 A/m ² , and even more preferably at least 280 A/m ² . Higher current density through the cell usually has the advantage of increasing cell performance, in particular if the current contribution to copper cation transport is kept high and the portion of the current that is used by mechanisms not contributing to copper cation transport from anode to cathode , is kept low, for example by keeping the amount of iron cations in the electrolyte low, for example when using anodes containing iron below a predetermined limit.

In one embodiment of the present invention, the current density through the cell is at most 400 A/m ² , preferably at most 390 A/m ² , more preferably at most 380 A/m ² , even more preferably at most 370 A/m ² , preferably at most 360 A/m ² , more preferably at most 350 A/m ² , still more preferably at most 340 A/m ² , preferably at most 330 A/m ² , more preferably at most 320 A/m ² , still more preferably at most 310 A/m ² , preferably at most 300 A/m ² , more preferably at most 290 A/m ² , and even more preferably at most 280 A/m ² . Applicants have found that adhering to the prescribed upper limit of cell current density has the advantage that problems exacerbated by higher current density remain manageable and the beneficial effects of the present invention are more easily achieved. These problems have been described elsewhere in this document, and anodic passivation is a prime example of such a problem.

In one embodiment of the present invention, the electrolyte is removed from the cell at an average renewal rate of greater than 30%, preferably at least 35%, more preferably at least 40%, even more preferably at least 45%, preferably at least 50%, more preferably at least 55%, even more preferably at least 60% per hour, preferably at least 70%, more preferably at least 75%, even more preferably at least 80%, preferably at least 85%, more preferably at least 90%, even more preferably at least 95%, preferably at least 100%, more preferably at least 105%, and even more preferably at least 110% per hour. The update rate and its average have been defined above. The indicated refresh rate takes into account only the volume of the first electrolyte flow leaving the cell by overflow. Any other electrolyte stream leaving the cell, such as the second electrolyte stream containing anode slimes, which is described later in this document, is in addition to the first stream's refresh rate. Applicants have found that a faster rate of electrolyte renewal is an important factor in controlling the amount of anode sludge in the cell. This is an important element in maintaining the high quality of the cathode despite the high level of impurities in the anodes. This additionally provides other benefits such as faster access to valuable anode sludge for further enrichment. The higher refresh rate also promotes increased agitation in the liquid bath present in the electrolytic cell. Higher liquid flows by themselves can cause some degree of liquid turbulence, at least locally, over and above the contribution of gas injection and bubbling, and hence do aid in reducing the thickness of stagnant liquid films that inevitably form on anode and/or cathode surfaces and facilitate the movement of copper cations from the anode to the cathode. Due to the upper limit of the iron content set for the anode composition, a higher renewal rate does not lead to a significant increase in the load caused by iron cations in the electrolyte.

In one embodiment of the present invention, the electrolyte is removed from the cell at an average renewal rate of at most 1700% per hour, preferably at most 1500%, more preferably at most 1200%, even more preferably at most 1000%, preferably at most 800%, more preferably at most 600%, even more preferably at most 400%, preferably at most 300%, more preferably at most 290%, even more preferably at most 250%, preferably at most 200%, more preferably at most 175%, still more preferably at most 150%, preferably at most 125% per hour. Applicants have found that compliance with the prescribed upper limit on the rate of electrolyte renewal has the advantage that fluid pressure on the electrodes can remain limited. This has the advantage that it may not be necessary to provide guides for all the electrodes in the bath to limit movement of the electrodes in the cell and to keep the spacing between adjacent electrodes within tight limits of desired (and usually design) values. Limiting the rate of electrolyte renewal to a specified upper limit has the advantage that heavy anode slimes are more likely to settle to the bottom of the cell, from which they can be removed during operation, as explained later in this document.

In one embodiment of the present invention, the amount of gas introduced into the cell and bubbled through the electrolyte between the anode and cathode is at least an effective amount, that is, an amount that effectively results in enhanced mixing of the electrolyte. The effective amount of gas provides a marked reduction in the cell voltage at the desired current density compared to the voltage set without the introduction of gas. The gas must be supplied at a pressure that is at least sufficient to overcome the hydrostatic pressure of the liquid column in the cell above the gas supply level, and preferably even higher. Applicants prefer to apply a pressure that is at least 0.1 bar above this minimum required pressure, preferably at least 0.3 bar, more preferably at least 0.5 bar above the hydrostatic pressure, together with a variety of flow restrictions, such as small holes or nozzles through which the gas is bubbled into the cell so that the pressure drop is set above the flow restrictions and the gas flow is better distributed over the plurality of flow restrictions and hence the resulting gas bubbles are also more evenly distributed throughout the cell.

In one embodiment of the present invention, the metal composition contains at least 90.5 wt.% copper, preferably at least 91.0 wt.%, more preferably at least 91.5 wt.%, preferably at least 92.0 wt.%, more preferably at least 92.5 wt.%, and even more preferably at least 93.0 wt.% copper.

Preferably, the molten liquid metal composition of the present invention also complies, where possible, with the concentration limits prescribed for the anode composition as part of the process of the present invention, and preferably also with the preferred concentration limits for the anode composition, but excluding the oxygen content. The benefits associated with these concentration features prescribed for the molten liquid metal composition of the present invention are the same as those described in the context of the anode composition as part of the process of the present invention.

In one embodiment, the molten liquid metal composition of the present invention contains at least 0.25 wt% nickel, preferably at least 0.50 wt%, more preferably at least 0.75 wt%, even more preferably at least 1.00 wt.%, preferably at least 1.25 wt.%, more preferably at least 1.50 wt.%, even more preferably at least 2.00 wt.%, preferably at least 2 10 wt.%, more preferably at least 2.25 wt.%, and even more preferably at least 2.50 wt.% nickel. The higher level of nickel in the metal composition allows the upstream process to accept more feedstock containing significant amounts of nickel. Such a feedstock is difficult to handle for most electrorefining operations and is therefore more readily available on more cost effective terms. Optionally, the metal composition contains at most 10.0 wt.% nickel, preferably at most 9.0 wt.%, more preferably at most 8.0 wt.%, even more preferably at most 7.00 wt.%, preferably at most 6.00 wt%, more preferably at most 5.50 wt%, preferably at most 5.00 wt%, more preferably at most 4.50 wt%, preferably at most 4.00 wt%, and more preferably at most 3.50 wt% nickel. At lower levels of nickel in the anode composition, the drain flow can be kept smaller, making it easier to further process and the associated operating costs. Lower nickel levels also reduce the need to add additional copper cations to the electrolyte. Less nickel also reduces anodic passivation, which allows measures to be taken to combat anodic passivation with less severity and/or intensity.

Applicants have found that it is important to have the oxygen content of the molten liquid metal composition of the present invention in accordance with a predetermined upper limit, preferably less than 3000 wt. ^ppm , more preferably at most 2800 wt. ^ppm , even more preferably at most 2600 wt. ^ppm , preferably at most 2500 wt. ^ppm , more preferably at most 2400 wt. ^ppm , even more preferably at most 2300 wt. ^ppm , more preferably at most 2200 wt. ^ppm , even more preferably at most 2100 wt. ^ppm , preferably at most 2000 wt. ^ppm , more preferably at most 1800 wt. ^ppm , even more preferably at most 1600 wt. ^ppm , and even more preferably at most 1400 wt. ^ppm . On the other hand, the applicants state that it is also important to maintain the oxygen content in accordance with the given lower limit, preferably at least 300 wt. ^ppm , more preferably at least 400 wt. ^ppm , even more preferably at least 500 wt. ^ppm , even more preferably at least 600 wt. ^ppm , preferably at least 700 wt. ^ppm , more preferably at least 800 wt. ^ppm , even more preferably at least 1000 wt. ^ppm , preferably at least 1250 wt. ^ppm , more preferably at least 1500 wt. ^ppm , even more preferably at least 1750 wt. ^ppm , and even more preferably at least 2000 wt. ^ppm .

In one embodiment of the present invention, the anode contains at least 75.0 wt.% copper, preferably at least 77.5 wt.%, more preferably at least 80.0 wt.%, even more preferably at least 82, 5 wt.%, preferably at least 85.0 wt.%, more preferably at least 87.5 wt.%, even more preferably more than 90.0 wt.%, preferably at least 90 wt.%, more preferably at least 91.0 wt.%, even more preferably at least 91.5 wt.%, preferably at least 92.0 wt.%, more preferably at least 92.5 wt.%, and even more preferably at least 93.0 wt.% copper. This has the advantage that the production of copper in the cell is higher and that the measures that are put in place to alleviate the problems caused by anode impurities are easier to provide and control. Thus, this offers the advantage of less anode slime to be removed and recycled, less anodic passivation, as well as higher cathode quality both in terms of composition, physical aspects and ease of stripping.

In one embodiment of the present invention, at least a portion of the anode slimes in the cell is removed from the cell with the first electrolyte stream. Applicants have found that the first flow of electrolyte by overflowing the cell wall is very suitable for carrying away some of the anode sludge that is constantly formed during the electrolytic cycle for a number of reasons, primarily due to impurities in the anode, as explained above. Applicants have found that with the first flow of electrolyte, the lower density, and therefore lighter, sludge particles are carried first.

In one embodiment of the present invention, the first electrolyte flow is maintained positive throughout the entire electrolytic cycle. Applicants prefer to maintain a positive liquid overflow throughout the electrolytic cycle so that at any time during the electrorefining operation the cell is kept full of liquid. This reduces and possibly avoids the risks associated with loss of liquid level in an electrolytic cell where an electrical arc becomes possible, for example between bare electrodes or between an electrode and an overhead crane above the cell, which could cause damage to equipment or pose a safety hazard.

In one embodiment of the present invention, the cell wall with overflow of the first electrolyte stream is a side wall that intersects the planes of the largest surfaces of the electrodes, with the cell preferably having a rectangular shape in plan (as viewed from above), and the side wall with overflow extending approximately perpendicular to the orientation electrodes. Such a side wall is usually the longest, which has the advantage that the fluid flow per unit length of the cell wall at the overflow can be reduced. This feature also has the advantage that the direction of the flow of electrolyte leaving the cell through the overflow has less effect on the electrode surfaces, which reduces the risk of movement of the electrodes under the influence of the flow of the outgoing electrolyte. Preferably, the direction of flow of the outgoing electrolyte is parallel to the surfaces of the electrodes, and there may be substantially no lateral pressure of the flow of the outgoing electrolyte on the electrodes. For this reason, Applicants prefer that the electrolyte flow over substantially the entire length of at least one sidewall of the cell, possibly interrupted for limited distances to pass structural members to support the top structure of the cell. Applicants have further found that this feature has the advantage of a more uniform distribution of electrolyte additives throughout the cell compared to supplying electrolyte from one short side of the cell and overflowing from the opposite short side of the cell, i.e., an arrangement in which all of the electrolyte runs the entire length of the cell and the concentration of additives gradually decreases due to consumption from entry to exit. The concentration of these additives is usually controlled at the entry point of the electrolyte into the cell. Since these additives are gradually consumed and/or destroyed on the surfaces of the cathodes as the electrolyte moves through the cell from inlet to outlet, this arrangement of electrolyte overflow improves the distribution of these additives throughout the bath.

In one embodiment of the present invention, the first electrolyte stream is passed through at least one settler providing a residence time high enough at a low enough liquid velocity to allow the anode sludge to settle to the bottom of the settler. Applicants have found that the sump is very suitable for collecting and removing most of the anode slimes carried away from the cell by the overflow before that electrolyte can be returned to the electrolytic cell. This step of removing anode sludge from the electrolyte overflow, especially when the purified electrolyte is recycled, is the first step in controlling the concentration of anode sludge in the electrolytic cell, in particular the fine and/or light particles of anode sludge that are formed during the electrolytic cycle. This greatly contributes to the fact that the anodes can contain higher levels of impurities. Applicants prefer to provide multiple settling tanks.

In one embodiment, a flocculant is added to the electrolyte on its way to the settler. This facilitates the coagulation of the particles and the settling of the anode slimes at the bottom of the sump. This has the additional advantage that less fine anode slimes are returned to the electrolytic cell, thereby improving the control of the presence of anode slimes in the cell and thus also the quality of the produced cathodes.

In one embodiment of the present invention, in which the process comprises a settler on the first electrolyte stream, a third electrolyte stream containing anode sludges is removed from the bottom of the settler. The creation of this third electrolyte stream represents the second step in controlling the concentration of anode sludge in the electrolytic cell, in particular the fine and/or light particles of anode sludge that are generated during the electrolytic cycle. This second stage ensures continuous operation of the sump, making it easier to operate, and at the same time provides more frequent access to the anode sludges collected at the bottom of the sump, with the corresponding benefits discussed elsewhere in this document in relation to easier access to the anode slimes. Applicants prefer to create this third stream containing anode slimes electrolyte discontinuously from the same sump. By allowing some time for an anode slime layer to form at the bottom of the settler, the third electrolyte stream can be richer in anode slime and its further processing can be more efficient, simple, efficient and beneficial.

In one embodiment of the present invention, a second electrolyte stream containing anode slimes is removed from the bottom of at least one electrolytic cell. Applicants have found that some of the anode sludge successfully sinks to the bottom of the cell and reaches the space in the cell below the level at which the gas is introduced. In this lower region, the liquid moves much more slowly, and the particles of anode slime reaching this region easily form an electrolyte layer very rich in anode slimes at the bottom of the cell. Applicants also prefer to remove this anode sludge by withdrawing the second electrolyte stream containing the anode sludge from the bottom of the electrolytic cell.

In one embodiment of the present invention, the second electrolyte stream is removed during the electrorefining operation from the bottom (bottom) section of the cell below the electrodes and designed to collect the anode sludge. Applicants have found that it is advantageous to remove the second stream from the cell during the electrolytic cycle, and more preferably while the electrorefining is in operation, i.e., while an electric current is passing through the cell. Applicants have found that it is possible to remove a second thread from a cell without interrupting its operation. This has the advantage over many processes described in the art that the cell does not need to be taken out of service to remove the layer of anode sludge that collects at the bottom of the cell, and that it is easier to control the presence of anode sludge in the cell throughout the entire electrolytic cycle. Applicants prefer to provide space in the cell below the electrodes, more preferably also below any equipment provided for injecting gas into the cell. In this lower space, the fluid flows more slowly and with less turbulence due to the absence of gas bubbles. Applicants prefer to provide electrolyte supply to the cell at a level which is higher than this lower section, so that the shortest liquid path between this liquid entry point and the electrolyte overflow through at least one wall of the cell does not pass through and therefore does not disturb the lower space provided for collecting the heavy part generated anode sludge.

In one embodiment of the present invention, a second and/or third stream of electrolyte containing anode slimes is sucked from the bottom of the cell and/or from the bottom of the sump, preferably by means of a suction head moving over the bottom of the cell and/or sump. Applicants, preferably at regular intervals during the electrolytic cycle and while the electrolytic cell is in operation, pass the suction pipe through the cell in the space provided below the electrodes, as well as under any equipment provided for introducing gas into the cell, but above the space provided in the lower section of the cell for collecting particles of anode sludge.

A suitable way to remove the second and/or third stream of electrolyte containing anode sludge is to suck the stream with a suction pipe that moves above the bottom of the cell and/or sump, preferably above the space intended to collect the layer of anode sludge. A suitable method for this feature is described in WO 00/79025 A1.

Applicants prefer to remove the bottom layer of anode slimes in the cell before the top of this layer reaches the level in the cell at which gas is introduced, preferably before the top of the layer reaches the level at which the suction pipe moves through the cell to draw in the second stream electrolyte from the bottom of the cell, preferably rich in anode slimes.

Applicants also prefer to provide similar means and precautions in the settling tanks through which the first electrolyte stream passes, its anode sludges should generally settle at the bottom of the settling tank, which produces an electrolyte depleted in anode sludges compared to the first electrolyte stream leaving the electrolytic cell.

In one embodiment of the present invention, the second electrolyte stream is combined with the first and/or third electrolyte stream into a combined electrolyte stream containing anode slimes. This has the advantage that these streams can be processed together, making further work easier.

In one embodiment of the present invention, the process comprises recycling to the electrolytic cell the electrolyte that has been removed from the cell. This recycling provides significant benefits. Recycling the electrolyte has the advantage that process chemicals in the electrolyte, such as sulfuric acid, are reused. An additional advantage is that compounds that remain dissolved in the electrolyte but tend to accumulate during the electrorefining operation can be concentrated to higher concentrations, making subsequent recovery of these compounds more efficient.

In one embodiment of the present invention, the process comprises removing a drain stream of electrolyte from a recycled electrolyte. Such a drain stream has the advantage that its removal rate is able to control the concentration of those compounds in the electrolyte that tend to accumulate in the electrolyte and remain in solution. One such compound is nickel sulfate, for which the solubility limit is significant.

In one embodiment of the present invention, the effluent undergoes at least one electrochemical recovery step. Applicants have found that it is advantageous to recover specific metals from this effluent stream. The effluent contains significant levels of copper, and much of it can easily be selectively recovered by electrochemical copper recovery. The effluent may also contain significant levels of nickel. This nickel can also be selectively reduced by electrowinning nickel, a process that is similar to, but somewhat different from, electrowinning copper, and which functions better when the copper content of the electrolyte is reduced to at most 20 grams/litre, preferably at most 15 gram/liter, more preferably at most 10 gram/liter, even more preferably at most 5 gram/liter, even more preferably at most 1 gram per liter, preferably at most 750 milligrams/liter, more preferably at most 500 milligrams/liter, even more preferably at most 250 milligrams/liter, preferably at most 100 milligrams/liter, more preferably at most 50 milligrams/liter, and even more preferably at most 10 milligrams/liter.

In one embodiment of the present invention, most of the metals are removed from the overflow stream, thereby forming a "black acid" stream, ie a concentrated acid stream. This black acid stream is usually and preferably more concentrated in acid than the electrolyte. Applicants prefer to remove metals, in particular nickel, by evaporating the water from the effluent, preferably after reducing the copper content as described above. Due to this evaporation, the nickel sulfate is concentrated to a level above its solubility limit and crystallized. The nickel sulfate crystals can then be recovered by precipitation, filtration, centrifugation, or combinations of the above.

In one embodiment of the present invention, the black acid stream is recycled to the electrolytic cell, preferably the black acid stream is recycled after additional copper cations have been added to the black acid. This has the advantage that most of the acid in the effluent can be reused and less refreshing acid is required to maintain its concentration in the electrolyte at the desired level. Applicants have further found that black acid, due to its high acid concentration, especially when it is higher than the concentration in the electrolyte present in the cell, is very suitable for dissolving copper, which will be discussed later in this document. Along with maintaining the acid concentration in the electrolyte, the black acid recycle, including additional copper cations, helps to maintain the desired working concentration of copper cations in the electrolyte.

In one embodiment of the present invention, the anode sludge is separated from at least one of the first, second and/or third electrolyte streams, preferably from the combined electrolyte stream containing the anode sludge, preferably before the drain electrolyte stream is removed from the recirculating electrolyte, preferably the anode sludge is removed as a solid, more preferably using a filter press or a tube press. This has the advantage of controlling the concentration of anode slimes in the electrolytic cell. Applicants prefer this separation of the anode slime from the electrolyte to be as clean as possible in order to reduce the by-product of the anode slime by containing copper and/or nickel, at least copper and/or nickel, which are present in dissolved form in the electrolyte.

In one embodiment of the present invention, in which the anode sludge is removed as a solid and in which the solid anode sludge is washed with water prior to removing the anode sludge by-product from the overall process, the wash water is recycled to the electrorefining process. The same wash water may be additionally used after the described washing step and/or may be used prior to the described washing step for other useful functions such as washing spent anodes and/or cathodes after they have been removed from the electrolytic cell, and/or for dissolving ingredients that must be added to the electrolytic cycle, such as additives or additional copper cations, before being reused in the electrorefining process.

Washing the hard anode slimes has the advantage that less soluble metals, in particular copper and/or nickel, leave the process along with the anode slime by-product, where they are of little value but usually represent an extra overhead. By recycling this used wash water, more of these soluble metals can remain in the process and can then be more conveniently removed as part of the overflow from which they can be more easily recovered.

In one embodiment of the present invention, in which the solid anode slimes are washed with water, the aqueous washing of the anode slimes is carried out at a temperature of at least 40°C, preferably at least 50°C, more preferably at least 60°C, even more preferably at at least 65°C, and at most 90°C, preferably at most 85°C, more preferably at most 80°C, and even more preferably at most 75°C. Applicants have found that a higher water flush temperature helps flush out sulfate salts from solid anode slimes, in particular copper sulfate and/or nickel sulfate. Since the used wash water is returned to the electrolyte cycle, it is advantageous for this wash water to be at a temperature close to the desired electrolyte temperature because it reduces the need for heating and/or cooling in order to ensure proper heat in the electrolyte cycle. Applicants have also found that compliance with a predetermined upper temperature limit reduces the risk of damage to the structural material of the equipment. The filter plates of the filter or filter press used to contain the anode slimes during water washing can be made of, for example, polypropylene, and applicants have found that this material is less susceptible to wear at a temperature corresponding to the specified upper limit.

In one embodiment of the process of the present invention, the anode sludge that has been recovered, preferably after washing with water, is treated with a sufficient amount of base, preferably NaOH, to convert most of the metal sulfates to a soluble sulfate salt such as Na ₂ SO ₄ and insoluble metal hydroxides . Thus, the sulfur content in anode slimes can be reduced, which makes them more suitable for the subsequent extraction of metals, incl. because their concentration becomes higher. Metal recovery processes are generally better suited for treating metal oxides and/or hydroxides. Often, other types of feedstock are preferably calcined to produce oxides before the metals can be recovered.

The hydroxides are preferably heated to form oxides, and the pyrometallurgical process step carried out in the furnace using a reducing agent such as iron can recover polymetallic solder from anode slimes and iron oxide containing slag as a by-product. In order to extract more Sn from the slag into the metal phase and improve the physical phase separation between the solder phase and the slag phase, additional lead may be added, preferably until the tin/lead weight ratio in the metal phase is close to 1/3 .

In one embodiment of the present invention, additional copper cations are introduced into the electrolyte in the cell. Applicants have found that several contaminant metals in the anode draw an electrical current when they go into solution in an electrolyte, in excess of the current drawn by the anode copper going into solution. At the cathode, this excess current causes more copper to be deposited than is dissolved at the anode. Thus, more copper is deposited on the cathode than goes into solution on the anode. This imbalance represents a net consumer of copper from the electrolyte. To make up for this net consumption, additional copper cations are added to the electrolyte in the electrolytic cell. Applicants have found that copper imbalance becomes more important as the level of impurities in the anode increases. While conventional electrorefining operations that start with anodes containing 98-99 wt.% copper usually work without adding additional copper cations to the electrolyte, Applicants have found that this addition is very useful in the process of the present invention, in which the anodes contain less copper and more other metals. Applicants have found that this addition allows the process to operate for a long period of time with high electrolyte recirculation and a high concentration of copper cations in the electrolyte, which is particularly advantageous at the cathode where the high concentration promotes high process performance with reduced power consumption and better cathode quality. In fact, Applicants have found that adding additional copper cations to the electrolyte helps to maintain the concentration of copper cations at desired levels, which is important to maintain high quality copper cathode production over a long period of time without creating additional operational problems. Applicants have found that this problem is more important for anode compositions that contain higher levels of impurities. Applicants have also found that this feature avoids the need to stop operation due to a decrease in the concentration of copper in the electrolyte below the minimum desired level, as, for example, in some processes disclosed in the art.

In one embodiment of the present invention, in which additional copper cations are added to the electrolyte, additional copper cations are introduced into the electrolyte supplied to the cell, preferably into the electrolyte returned to the electrolytic cell. Applicants have found that this is a very convenient way to maintain the concentration of copper in the electrolyte at the desired level.

In one embodiment of the present invention, in which additional copper cations are added to the electrolyte, a liquid stream containing at least a portion of the recycled electrolyte, and/or a stream that is even more concentrated in acid, such as at least a portion of the recycled black acid, or at least a portion of the effluent stream after copper removal by electrowinning, if present, or at least a portion of the fresh acid added to the process is contacted with a copper-bearing solid to dissolve more copper in the liquid stream, preferably in a vessel for leaching before the liquid stream with additional copper cations is transferred to the electrolytic cell. Applicants find these streams very suitable for dissolving copper from a copper-bearing solid and, therefore, for capturing additional copper cations, which are useful for controlling the concentration of copper in the electrolyte located in the electrolytic cell. Applicants prefer to use a stream that is available and that is more acidic than the electrolyte. A suitable stream is, for example, a black acid return stream because this stream is more acidic and therefore more readily dissolves copper from a solid source. The volumes of this returned black acid stream, however, are relatively small compared to the supply of electrolyte in the process, and it may also be available only occasionally. The process usually also needs to be fed with acid, for example, to compensate for the loss of acid to form nickel sulfate and/or lead sulfate. Such an acid make-up stream can also be a highly concentrated acid stream, such as sulfuric acid at a concentration of at least 50 wt.%, possibly even 96 wt.%, which in this case is also capable of more easily dissolving copper from a solid source compared to the electrolyte, which is returned to the cell. Make-up volumes are also relatively small and cannot be added continuously. Applicants therefore prefer to use an acidic stream that is more concentrated than the electrolyte returning to the cell, such as a black acid return stream and/or a sulfuric acid make-up stream, when available, but they also prefer to use the electrolyte return stream to take some additional copper cations on their way to the cell.

In one embodiment of the present invention, the copper-containing solid is in the form of granules, preferably hollow and open, optionally granules produced in a prior pyrometallurgical process step. Applicants have found that it is preferable for the copper-containing solid to be in finely divided form compared to large blocks, because the finely divided form provides a large contact surface of the extracting liquid for the same amount of solid. Applicants have found that granules are easier to handle than powder. The pellets can be easily placed in the leaching tank and can be held in the tank by a simple mesh trap provided on the liquid outlet. Preferably, the granules are hollow, which provides more contact surface for the same weight of solids. Applicants have found that it is very convenient for the copper-bearing material pellets to be produced in a pyrometallurgical process step prior to the process of the present invention. Most conveniently, this prior process step is part of the process producing the copper intermediate used to cast the anodes that are used in the electrolytic step of the process of the present invention. The substance of the pellets may be identical to that used for the anodes or may be of a different quality. Preferably, the pellets consist of copper material of higher purity than the anodes.

Applicants prefer to produce fine high surface area copper pellets by spraying liquid molten copper onto a refractory brick above the level of a large reservoir containing a cold liquid such as water. The flow of liquid molten copper breaks on the refractory brick and enters the cold liquid. This has the advantage of localized high vaporization similar to an explosion, and indeed forms fine high surface area copper pellets or "shot" which are very suitable for dissolution in an acidic liquid.

Applicants prefer to provide at least one vessel or tower for leaching and adding additional copper cations to the process. Such a container may be a vertical cylindrical container. This container can be opened at the top to the atmosphere, so that copper-containing solids can be easily introduced into this container. The solids may form a layer on the base at the bottom of the vessel, above the liquid inlet. The liquid inlet is conveniently provided below the base for this layer. The liquid flows upward through the layer of solids and leaves the tank through the overflow line. The vessel is preferably designed such that the upward flow rate of the liquid is low and the density of the copper containing solids is sufficient to avoid being carried away from the leaching vessel by the liquid flow. Preferably, the copper-containing solids are of high purity, such as blister copper, at least 98 wt% Cu. As the copper dissolves, the layer height decreases and the copper solids can be replenished through the open top of the vessel.

In one embodiment of the present invention, an oxygen-containing gas is added at the stage of contacting the liquid stream with a copper-containing solid. Applicants have found that copper from pellets more easily goes into solution in an acidic leach liquid under an oxidizing atmosphere. Preferably, Applicants inject air or enriched air, even more preferably commercially available oxygen gas, into the bottom section of the leach vessel, preferably below the bottom of the bed on which the solids are held. Applicants have found that the presence of oxygen in the leaching step greatly facilitates the capture of copper cations in the leaching liquid.

In one embodiment of the present invention, additional sulfuric acid is introduced into the process, preferably in the recycled electrolyte, if present, preferably with or before the addition of additional copper cations, if present. This feature provides a replenishing flow of sulfuric acid, useful for managing the sulfuric acid content of the electrolyte, which may otherwise be depleted due to consumption of the sulfate anion in lead and/or nickel sulfate. As discussed above, applicants prefer to use a source of concentrated sulfuric acid for this replenishment, such as 96 wt% sulfuric acid, and prefer to introduce this make-up acid where it comes into contact with copper-bearing solids to capture additional copper cations. The advantage of high concentration acid make-up is that it poses little risk of introducing unwanted elements into the process. An additional advantage is that much less volume is required and there are fewer handling difficulties compared to a less concentrated stream, and that the copper dissolves more easily.

In one embodiment of the present invention, the gas that is introduced into the cell is air. Applicants prefer to use air to sparge through the electrolytic cell, rather than its possible alternatives - nitrogen, carbon dioxide or even sulfur dioxide (SO ₂ ), as suggested in US patent 1260830 and in the article EN Petkova in "Mechanisms of floating slime formation and its removal with the help of sulfur dioxide during the electrorefining of anode copper", Hydrometallurgy, Vol. 46, Issue 3, October 1997, pp. 277-286. Applicants prefer air because of its convenience and improved aspects of safety and industrial hygiene. The use of nitrogen and/or carbon dioxide may result in the risk of inadvertent exposure of personnel to oxygen deficient atmosphere clouds. Sulfur dioxide is a toxic gas with a pungent, irritating odor and therefore requires even more stringent safety and industrial hygiene measures. Air has the added advantage of being an oxidizing agent, which is very convenient as it is able to oxidize As ³⁺ to As ⁵⁺ and/or Sb ³⁺ to Sb ⁵⁺ , whereby these metals become capable of forming compounds, usually salts. , such as arsenates, or oxides, which sink more easily to the bottom of the cells and/or settling tanks and collect in the anode sludge layer. These phenomena are described in more detail in C. A. Mcller et al, "Effect of As, Sb, Bi and Oxygen in Copper Anodes During Electrorefining", Proceedings of Copper 2010, pp. 1495-1510. Air is a much more convenient oxidant for applicants than sulfur dioxide for the reasons outlined above.

In one embodiment of the present invention, the gas introduced into the cell is at a temperature in the electrolyte temperature range of +/-30 degrees Celsius. This reduces any thermal effects that the introduction of the gas may locally create in the cell. Preferably, the temperature of the gas differs from the temperature of the electrolyte in the cell by at most 25 degrees Celsius, more preferably at most 20 degrees Celsius, and even more preferably at most 15 degrees Celsius. Local temperature drops are undesirable because it may cause local crystallization of some salts, for example around openings in a gas distributor, which may impair gas flow through these openings. Local temperature rise is also undesirable because it may cause some of the processing aids to decompose more quickly. Applicants prefer to introduce gas into the cell at a temperature of approximately 45°C. Applicants prefer to maintain the electrolyte in the cell at a temperature in the range of 65-70°C, preferably about 68°C.

In one embodiment of the present invention, the gas introduced into the cell is at least saturated with water at the gas injection temperature. This reduces the risk of crystallization in and around the opening through which the gas enters the electrolyte.

In one embodiment of the present invention, water, preferably in the form of an aerosol, is injected into the gas before it is introduced into the cell. Applicants prefer to inject water with a low sodium content, preferably below the detection limit, preferably the injected water is produced by reverse osmosis. Applicants have found that this feature reduces the formation of salts at the points of entry of gas into the electrolyte, as well as any microporous polymer sleeve that may be provided around the tubes of the gas diffuser.

In one embodiment of the present invention, the gas bubbles passing through the electrolyte have an average diameter in the range of 1-3 mm. Applicants have found that gas bubbles with a diameter of at most 3 mm are more effective in removing depleted electrolyte adjacent to cathode surfaces in order to allow fresh electrolyte to come into contact with the cathodes. Fine bubbles also tend to minimize the formation of acid mist over the electrolysis cell. Smaller bubbles are also preferred because they create a regime in the cell that becomes similar to the so-called "dissolved air flotation" (DAF) regime, so that fine particles of anode slimes easily rise to the surface of the liquid column and easily leave the cell through the overflow. The size of the gas bubbles can be determined, for example, according to Reza Al Shakarji et al, in "The sizing of oxygen bubbles in copper electrowinning", Hydrometallurgy, 109 (2011), pp. 168-174.

In one embodiment of the present invention, gas is introduced into the cell through a gas diffuser provided below the electrodes but above the space provided at the bottom of the cell to collect the anode sludge layer, preferably a gas diffuser comprising selectively perforated diffuser tubes connected to the gas supply pipe. The location of the gas diffuser divides the vertical height of the electrolyte volume into two parts: the upper part, through which gas bubbles rise, which give more turbulence, and the lower part without gas bubbles, which is more stagnant, especially if the electrolyte supply is also provided approximately at the height of the gas diffuser . The additional turbulence at the top provides the benefits discussed in detail above. The smoother movement of the fluid at the bottom makes it easier for the anode sludge particles to settle to the bottom of the cell. Applicants prefer to use a diffuser as described in WO 2005/019502 A1 using a plurality of hoses made of and/or incorporating microporous material to allow bubbled gas to pass through the microporous material to form a plurality of fine bubbles in the electrolyte present in the cell.

Applicants have found that the diffuser preferably provides an evenly distributed presence of gas bubbles throughout the top of the electrolyte volume. The inhomogeneity in the presence of gas bubbles can lead to a difference in hydrostatic pressure across the electrode, which creates the risk that the electrode can be deflected to the side and come into contact and therefore cause an electrical short circuit with an adjacent counter electrode.

Applicants prefer to provide a gas injection density gradient such that less gas is injected closer to the overflow cell wall and more gas is injected closer to the opposite cell wall. This has the advantage that the gas gradient provides additional driving force for the liquid flow in the direction of the overflow.

In one embodiment of the present invention, gas is introduced into the cell using supply line pressure at a liquid level in the cell of at least 0.5 barg (barg), preferably at least 0.6 barg. , and more preferably at least 0.7 bar man. This overpressure is necessary to overcome the hydrostatic pressure at the point of gas entry into the cell, preferably below the electrodes. Applicants prefer to provide higher overpressure than hydrostatic pressure alone in order to improve the bubbling of the gas into the liquid and the formation of smaller bubbles. The pressure at said point in the supply line is preferably at most 3.5 barg, preferably at most 3.0 barg, more preferably at most 2.5 barg, even more preferably at most 2.0 barg. , preferably at most 1.75 barg, more preferably at most 1.50 barg, and even more preferably at most 1.25 barg. Compliance with this upper limit reduces the risk of electrolyte ejection from the cell, as well as the formation of nickel aerosols. Electrolyte release can cause damage to equipment and nickel aerosols create an industrial hygiene problem.

First of all, for reasons of industrial hygiene, applicants prefer to provide a hood over the cell, equipped with an exhaust pipe and a droplet eliminator, in order to avoid droplets of acid, possibly containing metal particles, from entering the workplace.

In one embodiment of the present invention, the electrolyte in the cell is maintained at a temperature in the range of 20°C to 75°C. Preferably, the temperature of the electrolyte in the cell is at least 25°C, more preferably at least 30°C, even more preferably at least 35°C, preferably at least 40°C, more preferably at least 45°C, even more preferably at least 50°C, preferably at least 55°C, more preferably at least 60°C, even more preferably at least 65°C, preferably above 65°C. Higher temperatures improve the diffusion rate of copper and this is particularly useful for the diffusion of copper cations through stagnant or laminar flow films that are typically present on anode and/or cathode surfaces. Higher temperatures also increase the solubility of sulfates in the electrolyte and therefore reduce the risk of crystallization, especially in sensitive locations. Applicants prefer to maintain the electrolyte at a temperature below 75°C, preferably at most 72°C, and more preferably at most 70°C. This has the advantage that additives that are temperature sensitive, such as gelatin and/or many flocculants, become more stable and less prone to degradation. The lower temperature also reduces the risk of cathode pre-peeling, that is, that the deposited copper layer will separate from the stainless steel workpiece while the cathode is still in the electrolytic cell. The lower temperature also reduces the cost of maintaining the temperature of the electrolyte, which is usually higher than the ambient temperature and therefore requires heat.

In one embodiment of the present invention, the composition of the anode and/or molten liquid metal composition of the present invention contains at least 0.25 wt.% nickel, preferably at least 0.50 wt.%, more preferably at least 0.75 wt. .%, even more preferably at least 1.00 wt.%, preferably at least 1.25 wt.%, more preferably at least 1.50 wt.%, even more preferably at least 2.00 wt. %, preferably at least 2.10 wt.%, more preferably at least 2.25 wt.%, even more preferably at least 2.50 wt.%, preferably at least 2.75 wt.%, and more preferably at least 3.00 wt% nickel. The higher level of nickel in the anode allows the upstream process to accept more feeds containing significant amounts of nickel. Such feedstocks are difficult to handle for most electrorefining operations and are therefore more readily available on more cost effective terms. Optionally, the anode composition contains at most 10.0 wt% nickel, preferably at most 9.0 wt%, more preferably at most 8.0 wt%, even more preferably at most 7.00 wt%, preferably at most more than 6.00 wt%, more preferably at most 5.50 wt%, preferably at most 5.00 wt%, more preferably at most 4.50 wt%, preferably at most 4.00 wt%, and more preferably at most 3.50 wt% nickel. At lower levels of nickel in the anode composition, the drain flow can be kept smaller, making it easier to further process and the associated operating costs. Lower nickel levels also reduce the need to add additional copper cations to the electrolyte. Less nickel also reduces anodic passivation, which allows measures to be taken to combat anodic passivation with less severity and/or intensity. Less nickel also reduces the industrial hygiene problems associated with nickel aerosols.

In one embodiment of the present invention, the composition of the anode and/or molten metal composition of the present invention contains at least 0.25 wt.% lead, preferably at least 0.50 wt.%, more preferably at least 0.75 wt. .%, even more preferably at least 1.00 wt.%, preferably at least 1.25 wt.%, and more preferably at least 1.50 wt.% lead. Allowing a higher level of lead in the anode allows the upstream process to operate with less harshness in relation to the separation between lead and copper, as well as accept more raw materials containing significant amounts of lead. Such raw materials are difficult to handle for many copper production operations and are therefore more readily available on more cost effective terms. Optionally, the anode composition contains at most 6.00 wt.% lead, preferably at most 5.00 wt.%, more preferably at most 4.00 wt.%, even more preferably at most 3.00 wt.%, even more preferably at most 2.50 wt.%, even more preferably at most 2.00 wt.%, even more preferably at most 1.80 wt.%, even more preferably at most 1.60 wt.%, and even more preferably at most 1.50 wt.% lead. With a lower lead content in the anode, less lead sulfate is formed in the cell. Therefore, the consumption of acid for the formation of lead sulfate is reduced. Lead sulfate has a very low solubility in the electrolyte and therefore easily crystallizes in the cell. These crystals have the risk of falling into the cathode. Therefore, a lower level of lead in the anode reduces the risk of lead entering the cathode as an impurity. Lead deposits are preferably removed from the cell as part of the anode slimes in the first electrolyte stream and/or in the second electrolyte stream. Since the presence of lead does not significantly affect the cost of the anode slime produced in the process, but contributes to the anode slime processing workload, a lower lead content in the anode is advantageous as it reduces the volume of anode slime and therefore the operating load without reducing the cost of the anode sludge by-product. The lower lead content of the anode also reduces the likelihood of lead being released into the workplace during human intervention, such as when anode sludge is discharged from a filter press, which is associated with industrial hygiene concerns.

In one embodiment of the present invention, the composition of the anode and/or molten liquid metal composition of the present invention contains at least 0.25 wt.% tin, preferably at least 0.50 wt.%, more preferably at least 0.75 wt. .%, even more preferably at least 1.00 wt.%, preferably at least 1.25 wt.%, and more preferably at least 1.50 wt.% tin. Allowing a higher level of tin in the anode allows the upstream process to operate with less harshness in relation to the separation between tin and copper, as well as accept more raw materials containing significant amounts of tin. Such raw materials are difficult to handle for many copper production operations and are therefore more readily available on more cost effective terms. In addition, the tin in the anode slimes is quite easily recovered from them and represents a significant portion of the commercial value derived from the by-product of the anode slimes from the process of the present invention. Optionally, the anode composition contains at most 6.00 wt.% tin, preferably at most 5.00 wt.%, more preferably at most 4.00 wt.%, even more preferably at most 3.00 wt.%, even more preferably at most 2.50 wt.%, preferably at most 2.00 wt.%, more preferably at most 1.80 wt.%, and even more preferably at most 1.60 wt.% tin. At lower levels of tin in the anode formulation, the volume of anode slimes decreases because the tin mostly leaves the process as tin oxide or tin and antimony, which is expected to end up in the anode slimes. Therefore, less tin in the anode reduces the cost of processing anode slimes. A lower level of tin in the anode reduces the risk of tin entering the cathode as an impurity. Less tin also reduces the risk of growth of solid SnSb compounds on the wetted surfaces of the electrolytic cycle, in particular in and around the electrolytic cells.

In one embodiment of the present invention, the composition of the anode and/or molten liquid metal composition of the present invention contains at least 0.10 wt.% antimony, preferably at least 0.15 wt.%, more preferably at least 0.20 wt. .%, even more preferably at least 0.25 wt.%, preferably at least 0.30 wt.%, more preferably at least 0.35 wt.%, preferably at least 0.40 wt.%, and more preferably at least 0.50 wt.% antimony. Allowing a higher level of antimony in the anode allows the upstream process to operate with less harshness to the separation between antimony and copper, as well as accept more feeds containing significant amounts of antimony. Such raw materials are difficult to handle for many copper production operations and are therefore more readily available on more cost effective terms. Optionally, the anode composition contains at most 3.00 wt.% antimony, preferably at most 2.50 wt.%, more preferably at most 2.00 wt.%, even more preferably at most 1.50 wt.%, even more preferably at most 1.25 wt.%, preferably at most 1.00 wt.%, more preferably at most 0.90 wt.%, and even more preferably at most 0.80 wt.% antimony. Lower levels of antimony in the anode composition reduce the risk of formation of oxide SnSb compounds, which can fall out of solution and form solid deposits and grow on the wetted surfaces of the electrolytic cycle, in particular in and around the electrolytic cells. A lower level of antimony in the anode reduces the risk of antimony entering the cathode as an impurity. Antimony is preferably removed from the cell as part of the anode slimes in the first electrolyte stream and/or in the second electrolyte stream, usually in the form of an intermetallic oxide such as antimony tin oxide. Since the presence of antimony has little to no effect on the cost of the anode slime produced in the process, but contributes to the anode slime processing workload, a lower antimony presence in the anode is advantageous as it reduces the volume of anode slime and thus the operating load without reducing the cost of the anode sludge by-product.

In one embodiment of the present invention, the composition of the anode and/or molten liquid metal composition of the present invention contains at least 0.010 wt.% bismuth, preferably at least 0.015 wt.%, more preferably at least 0.020 wt.%, even more preferably at least 0.025 wt.%, preferably at least 0.030 wt.%, and more preferably at least 0.035 wt.% bismuth. Allowing a higher level of bismuth in the anode allows the upstream process to operate with less harshness in relation to the separation between bismuth and copper, as well as accept more feeds containing significant amounts of bismuth. Such raw materials are difficult to handle for many copper production operations and are therefore more readily available on more cost effective terms. Optionally, the anode composition contains at most 0.50 wt.% bismuth, preferably at most 0.25 wt.%, more preferably at most 0.200 wt.%, even more preferably at most 0.150 wt.%, even more preferably at most 0.100 % wt., preferably at most 0.090 wt.%, more preferably at most 0.080 wt.%, and even more preferably at most 0.070 wt.% bismuth. A lower level of bismuth in the anode reduces the risk of bismuth entering the cathode as an impurity. Bismuth is preferably removed from the cell as part of the anode slimes in the first electrolyte stream and/or in the second electrolyte stream, presumably as bismuth metal and/or as an arsenate such as BiAsO ₄ if sufficient arsenic is present. Since the presence of bismuth has little to no effect on the cost of the anode slime produced in the process, but contributes to the anode slime processing workload, a lower presence of bismuth in the anode is advantageous as it reduces the volume of anode slime and thus the operating load without reducing the cost of the anode sludge by-product.

In one embodiment of the present invention, the composition of the anode and/or molten liquid metal composition of the present invention contains at least 0.0010 wt.% zinc, preferably at least 0.0050 wt.%, more preferably at least 0.0075 wt. .%, even more preferably at least 0.010 wt.%, preferably at least 0.015 wt.%, and more preferably at least 0.020 wt.% zinc. Allowing for a higher level of zinc allows the upstream process to be less stringent in removing zinc from the copper containing streams resulting in an anode composition, as well as accepting more feed which contains significant amounts of zinc. Such raw materials are difficult to handle for many copper production operations and are therefore more readily available on more cost effective terms. Optionally, the anode composition contains at most 0.50 wt. % zinc, preferably at most 0.25 wt. %, more preferably at most 0.200 wt. wt%, more preferably at most 0.090 wt%, preferably at most 0.080 wt%, more preferably at most 0.070 wt%, preferably at most 0.050 wt%, and more preferably at most 0.025 wt% zinc. A lower level of zinc in the anode reduces the risk of zinc entering the cathode as an impurity. Zinc is preferably removed from the process as part of the drain from the electrolyte cycle and/or as part of the anode slimes in the first electrolyte stream and/or in the second electrolyte stream. Since the presence of zinc has little to no effect on the cost of the anode sludge and/or effluent produced in the process, but does contribute to the anode sludge and/or effluent processing workload, a lower presence of zinc in the anode is advantageous as it reduces the volume of anode sludge and therefore the operating load without reducing the cost of the anode sludge by-product. The same applies to the value of the drained stream and the costs of its processing.

In one embodiment of the present invention, the anode composition contains at least 0.005 wt.% arsenic, preferably at least 0.010 wt.%, more preferably at least 0.020 wt.%, even more preferably at least 0.025 wt.%, preferably at least at least 0.050 wt.%, more preferably at least 0.060 wt.%, even more preferably at least 0.070 wt.%, and even more preferably at least 0.075 wt.% arsenic. Allowing a higher level of arsenic in the anode allows the upstream process to be less stringent in removing arsenic from the copper-bearing streams resulting in an anode composition, as well as accept more feeds that contain significant amounts of arsenic. Such raw materials are difficult to handle for many copper production operations and are therefore more readily available on more cost effective terms. It is also claimed that arsenic reduces anodic passivation and is able to form intermetallic compounds such as arsenates such as SbAsO ₄ and BiAsO ₄ which readily fall out of solution and transfer other metal impurities to the anode slimes. Therefore, a compound with a higher arsenic content may also offer the advantage of reduced anodic passivation and faster removal of other impurity metals, causing them to become part of the anode slimes. Optionally, the anode composition contains at most 0.40 wt. % arsenic, preferably at most 0.30 wt. wt.%, preferably at most 0.150 wt.%, more preferably at most 0.125 wt.%, and even more preferably at most 0.100 wt.% arsenic. A lower level of arsenic in the anode reduces the risk of arsenic entering the cathode as an impurity. Arsenic is preferably removed from the cell as part of the anode sludges in the first electrolyte stream and/or in the second electrolyte stream, for example as the arsenate of another metal impurity such as antimony or bismuth, or as a mixed oxide such as 2As ₂ O ₅ ×3Sb ₂ O ₃ , or being bound and/or trapped in oxides of tin and/or tin and antimony. Since the presence of arsenic has little to no effect on the cost of the anode slime produced in the process, but does contribute to the anode slime processing workload, a lower anode arsenic presence is advantageous as it reduces the volume of anode slime and therefore the operating load without reducing the cost of the anode sludge by-product.

In one embodiment of the present invention, the composition of the anode and/or molten liquid metal composition of the present invention contains at least 0.0001 wt.% silver, preferably at least 0.0010 wt.%, more preferably at least 0.0050 wt. .%, even more preferably at least 0.0100 wt.%, preferably at least 0.0150 wt.%, more preferably at least 0.0200 wt.%, even more preferably at least 0.0250 wt. %, preferably at least 0.0300 wt.%, more preferably at least 0.0350 wt.%, and even more preferably at least 0.0400 wt.% silver. Silver easily leaves the process of the present invention, most often as part of the anode slimes, and contributes significantly to the cost of the by-product of the anode slimes of the process of the present invention. Thus, a higher silver content is preferred because it makes the processing of anode slimes and the recovery of the metals contained therein more economically advantageous. Optionally, the composition of the anode and/or molten liquid metal composition of the present invention contains at most 0.50 wt.% silver, preferably at most 0.25 wt.%, more preferably at most 0.200 wt.%, even more preferably at most 0.150 wt.%, even more preferably at most 0.100 wt.%, preferably at most 0.075 wt.%, more preferably at most 0.060 wt.%, and even more preferably at most 0.050 wt.% silver. A high silver content increases the risk of silver getting into the cathodes. The silver in the copper anode does not provide additional economic value and is therefore less valuable than the silver in the anode sludge. Silver is an undesirable impurity in cathode copper because it creates technical problems in the main end use of copper, ie copper wire drawing.

In one embodiment of the present invention, the anode composition contains at most 0.0500 wt.% or 500 wt. ^ppm oxygen, preferably at most 0.0400 wt.%, more preferably at most 0.0300 wt.%, even more preferably at most 0.0200 wt.%, even more preferably at most 0.0180 wt.%, preferably at most 0.0150 wt.%, more preferably at most 0.0125 wt.%, and even more preferably at most 0.0100 wt.% or 100 wt. ^ppm oxygen. Applicants prefer that the oxygen content be below a predetermined limit because the excessive presence of oxygen increases the risk of improper anode formation during casting and cooling, as explained elsewhere in this document. For this reason, Applicants prefer that the anode composition contains oxygen in an amount below a predetermined upper limit.

Optionally, the composition of the anode contains at least 0.0005 wt.% or 5 wt. ^ppm oxygen, preferably at least 0.0010 wt.%, more preferably at least 0.0015 wt.%, even more preferably at least 0.0020 wt.%, preferably at least 0.0025 wt. %, more preferably at least 0.0030 wt.%, even more preferably at least 0.0040 wt.%, preferably at least 0.0050 wt.%, more preferably at least 0.0075 wt.%, and even more preferably at least 0.0100 wt.% or 100 wt. ^ppm oxygen. Applicants have found that it is preferable not to reduce the oxygen content of the anode composition to very low levels. The cost and effort to achieve very low levels of oxygen in the anode formulation is not offset by an equivalent economic benefit. On the contrary, the additional efforts usually taken to further reduce the oxygen content to values below the specified lower limit are usually tedious, complicated, and also tend to remove some valuable metals from the anode composition, and therefore reduce its volume and create side flows with lower value. For this reason, applicants prefer to have the level of oxygen in the anode composition in accordance with the specified lower limit.

In one embodiment of the present invention, the anode composition is a molten liquid metal composition of the present invention, the oxygen content of which has been further reduced, preferably so that it reaches the concentration range specified for the anode composition of the process of the present invention, for example from 5 wt. ^ppm to 500 wt. ^ppm .

In one embodiment of the present invention, the composition of the electrolyte meets at least one, and preferably all of the following conditions:

- contains copper in the range of 20-55 grams/litre,

- contains nickel in the range of 25-90 grams/litre,

- contains sulfuric acid in the range of 130-200 grams/liter, preferably at most 190 grams/liter, more preferably at most 180 grams/liter, even more preferably at most 170 grams/liter, even more preferably at most 160 grams/liter, and optionally at least 140 grams/litre,

- contains tin in the range of 0.4-1.4 grams/liter, preferably at most 1.2 grams/liter, more preferably at most 1.0 grams/liter, even more preferably at most 0.90 grams/liter, still more preferably at most 0.80 grams/litre, and

- contains arsenic in the range of 10-200 milligrams/liter, preferably at least 15 milligrams/liter, more preferably at least 20 milligrams/liter, and optionally at most 175 milligrams/liter, preferably at most 150 milligrams/liter, more preferably at most 100 milligrams/liter, even more preferably at most 75 milligrams/liter, and most preferably at most 50 milligrams/liter.

Applicants have found that it is beneficial to maintain the dissolved copper content of the electrolyte within prescribed limits, since this range provides an excellent balance between its positive function at the cathode, where a high concentration promotes diffusion through a stagnant film on the cathode surface, and its possible negative functionality at the anode, where a high concentration reduces the driving force for diffusion through the stagnant film on the anode surface.

Applicants prefer to maintain the nickel content of the electrolyte within prescribed limits, preferably at least 30 grams/liter, more preferably at least 35 grams/liter, even more preferably at least 40 grams/liter, preferably at least 45 grams/liter, more preferably at least 50 grams/liter, even more preferably at least 55 grams/liter, preferably at least 60 grams/liter, and more preferably at least 65 grams/liter. A higher nickel content increases the value of the effluent from which the nickel can be recovered by further processing, due to the higher amount of nickel present and also because its recovery becomes more efficient. On the other hand, a higher nickel content in the electrolyte also increases the risk that locally, for example in cold places or in drops of electrolyte that have dripped onto parts of the equipment that are not immersed in the electrolyte, but may be hot, nickel sulfate precipitates out of solution and forms a solid substance which may impair or even hinder the correct operation of the equipment. For these reasons, Applicants prefer to maintain the nickel content of the electrolyte at a maximum of 85 grams/liter, preferably at a maximum of 80 grams/liter, more preferably at a maximum of 75 grams/liter, and even more preferably at a maximum of 70 grams/liter.

Applicants have found it beneficial to maintain the sulfuric acid content of the electrolyte within prescribed limits because this range provides an excellent balance between, on the one hand, its positive functions of dissolving metals from the anode and imparting electrical conductivity to the electrolyte, and, on the other hand, its possible negative functionality of increasing density and viscosity of the electrolyte, which impairs the mass and heat transfer and the settling rate of anode slimes and creates a risk of damage to equipment that may come into contact with the electrolyte. Higher concentrations of sulfuric acid may require the choice of more exotic and therefore expensive construction materials, ie additional capital costs that can be avoided by respecting the specified upper limit.

Applicants have found that tin dissolved in the electrolyte tends to form so-called "floating sludge", particles of anode sludge that do not sink to the bottom in the electrolytic cell and do not sink to the bottom in the settling tank, where the residence time can be much longer and the liquid velocity can be much smaller than in the cell. Thus, such floating cuttings are not removed from the electrolyte by the various process means described for removing anode cuttings.

Applicants desire to keep the arsenic level in the electrolyte below the specified upper limit. The presence of arsenic above the specified lower limit can be beneficial because it reduces the effect of the anodic passivation mechanism and can convert more other metallic contaminants to intermetallic compounds that are hard and become part of the anode slimes. However, more arsenic in the electrolyte than the specified upper limit may be disadvantageous because it results in more arsenic in the overflow, requiring additional processing to recover most of the metal it contains, and also introduces more arsenic into the anode sludge by-product. . A higher amount of arsenic can create an additional burden on the further processing of the anode slimes and/or effluent stream removed from the electrolytic cycle, to the extent that it may require an additional stage for their respective further processing. More arsenic does not increase the value of the by-product streams, and therefore the arsenic content is preferably kept below a predetermined upper limit. On the other hand, applicants have found that low levels of arsenic, in accordance with the specified lower limit, are acceptable because the additional cost or limitation imposed by requiring even lower arsenic content is not offset by the additional benefits of less arsenic.

In one embodiment of the present invention, at least one, and preferably all, of the following process chemicals are added to the electrolyte, as prescribed:

- surface-active components (eg gelatin) in the range of 25-900 grams/ton of produced cathode copper, preferably at least 50 grams/ton, more preferably at least 100 grams/ton, even more preferably at least 150 grams/ ton, preferably at least 200 grams/ton, more preferably at least 250 grams/ton, preferably at least 300 grams/ton, more preferably at least 350 grams/ton, even more preferably at least 400 grams/ton , even more preferably at least 450 grams/ton, preferably at least 500 grams/ton, more preferably at least 600 grams/ton, and optionally at most 800 grams/ton, preferably at most 700 grams/ton, more preferably at most 600 grams/ton, even more preferably at most 500 grams/ton, even more preferably at most 400 grams/ton, and most preferably at most over 350 grams/tonne of copper cathode produced,

- hydrochloric acid (HCl) in the range of 25-250 grams of HCl per ton of copper cathode produced,

- hydrobromic acid (HBr) in the range of 25-400 grams of HBr per ton of copper cathode produced,

- at least one flocculant in the range of 800-3000 milligrams per ton of copper cathode produced, preferably at least 1000, optionally at most 2500, preferably at most 2000, and more preferably at most 1500 milligrams/ton of copper cathode produced, and

- thiourea in the range of 15-150 grams per tonne of copper cathode produced.

Applicants prefer to add at least one surfactant component to the electrolyte. Applicants have found that surfactants reduce/eliminate dendritic growth on cathodes and thus reduce the risk of short circuits. Applicants have found that gelatin is a very suitable surfactant component. Applicants have found that the prescribed addition range, and typically about 650 grams of gelatin per tonne of copper cathode produced, is reasonably effective without creating additional problems or unexpected operating costs.

Applicants prefer to add hydrochloric acid (HCl) to the electrolyte. Hydrochloric acid has the advantage that the polymerization of any gelatin that may be added is reduced and its polymer chains are cut into small pieces so that the gelatin retains its activity. More importantly, the chlorine from hydrochloric acid is capable of sequestering silver (Ag) in an insoluble form (AgCl) which is easily incorporated into anode slimes and can be conveniently removed from the process so that most of the silver can be recovered economically. Applicants prefer to add at least 30 grams of hydrochloric acid per ton of copper cathode produced, preferably at least 50 grams, more preferably at least 75 grams, even more preferably at least 100 grams per ton of copper cathode produced, and optionally at most 225 grams, preferably at most 200 grams, more preferably at most 175 grams, and most preferably at most 150 grams per tonne of copper cathode produced. Applicants find it most convenient to introduce hydrochloric acid as a solution at a concentration of 30 wt.% and prefer to add about 430 milliliters of this solution per ton of copper cathode produced, but other concentrations can be used if necessary.

Applicants prefer to add to the electrolyte also hydrobromic acid (HBr) in the indicated dosing range. Applicants prefer to add at least 30 grams of hydrobromic acid per ton of copper cathode produced, preferably at least 50 grams, more preferably at least 75 grams, even more preferably at least 100 grams per ton of copper cathode produced, and optionally at most 350 grams, preferably at most 300 grams, more preferably at most 250 grams, and most preferably at most 200 grams per tonne of copper cathode produced. Applicants prefer to add typically about 125 grams of HBr per tonne of copper cathode produced. Hydrobromic acid provides the same benefits as hydrochloric acid. The addition of hydrobromic acid has the additional benefit that its silver salt (AgBr) is even less soluble than the chloride. Thus, hydrobromic acid has the advantage that it can remove more silver from the electrolyte into the anode slimes. Applicants prefer to use HBr in solution at a concentration of 48 wt.%, but other concentrations can be used if necessary. Applicants prefer to use both HCl and HBr as indicated.

Applicants prefer to add at least one flocculant to the electrolyte, preferably where the electrolyte enters the sumps, within the dosage range indicated, and typically in an amount of about 1035 milligrams per ton of copper cathode produced. We prefer to use adipic acid based cationic polyacrylamide which is available for example under the trademark ZETAG® type 7565.

Applicants also prefer to add thiourea to the electrolyte, preferably where the electrolyte enters the sumps, in an amount of 15-150 grams per ton of copper cathode produced, preferably at least 18, more preferably at least 20, even more preferably at least 25, even more preferably at least 30, and optionally at most 125 grams, preferably at most 100 grams, more preferably at most 75 grams, even more preferably at most 50 grams, even more preferably at most 49 grams, and typically about 32 grams of thiourea per ton of copper cathode produced. Thiourea is added to influence (together with the aforementioned process chemicals) deposit morphology (roughness and/or nodulation), crystal shape (round and/or sharp), and grain type (elongated and/or field oriented), which largely avoids the formation of nodules, porosity and dendrites on the cathode. More information on the functions of thiourea and other electrorefining additives has been described in Baumback J, Bombach H and Stelter M, "Investigations of the Behavior of Thiourea and alternative Additives in Copper Electrorefining", Proceedings EMC, 1 (2015), p 151-160 . Applicants prefer not to exceed this upper limit in order to keep the amount of sulfur in the cathodes low.

In one embodiment of the present invention, the cathode blanks are made of stainless steel, preferably SS316L or "duplex" steel. Applicants have found that the deposited layer of copper can be easily "stripped off" from a stainless steel workpiece, and the remaining workpiece can be easily reused with minimal processing as a new cathode running in an electrolytic cell.

In one embodiment of the present invention, the distance between the cathodes is at least 95 mm, preferably at least 100 mm, more preferably at least 105 mm, even more preferably at least 110 mm, preferably at least 115 mm, and more preferably at least 120 mm. Although a shorter distance between cathodes is advantageous for the electrical resistance of the cell, and thus also for the energy consumption of the electrorefining operation, Applicants have found that a high level of impurities in the composition of the anode creates additional risks of the formation and growth of dendrites, which cause a short circuit between the cathode and adjacent anode. In order to reduce the operator intervention required to clear such a short circuit, Applicants prefer to maintain the specified distance between the cathodes. Applicants have additionally found that greater cathode spacing benefits higher cathode purity despite lower anode purity.

Under the distance between cathodes in the context of the present invention is understood the distance from the midpoint of one cathode blank to the corresponding midpoint of an adjacent cathode blank, and it includes the thickness of one cathode and one anode in addition to twice the distance between the surface of the cathode and the surface of the adjacent anode facing cathode surface.

In one embodiment of the present invention, said at least one cathode is updated at a higher rate than the anode. Applicants prefer to replace cathodes in a cell with new blanks at a higher frequency than to replace spent anodes in the same cell with freshly cast anodes. This has the advantage of easier stripping of the cathodes because the deposited copper layer is thinner. An additional benefit is that the thinner copper layer on the cathode reduces the risk of damage to the workpiece during stripping. Another additional benefit is that the higher cathode refresh rate reduces the risk of a short circuit in the cell during the electrorefining operation. Such a short circuit requires operator intervention, which is labor intensive.

Applicants have found that it is possible and advantageous to partially replace the cathodes from one particular electrolytic cell, for example only one third of the cathodes at a time. This has the advantage that during the replacement of the cathodes the electrolytic cell can continue to operate even at its full capacity. Applicants find it advantageous to replace with blanks cathodes numbered 1, 4, 7, 10, etc., then cathodes numbered 2, 5, 8, 11, etc., and after that the remaining cathodes numbered 3, 6, 9, 12, etc. Applicants have found that it is possible to keep the electrolytic cell operational during the replacement of cathodes thus performed. Applicants have found that the cell can continue to operate fully and that 2/3 of the cathodes present in the cell are capable of withstanding the full current density for the short periods of time needed each time to replace 1/3 of the cathodes with new blanks.

Applicants have found that it is easy to reduce the oxygen content of the metal composition of the present invention to a level that is preferred by the anode composition as part of the process of the present invention. The advantages of bringing the oxygen content of the metal composition of the present invention within the limits prescribed for the composition of the anode as part of the process of the present invention are described elsewhere in this document.

Applicants prefer to reduce the oxygen content of the metal composition of the present invention through a process step known as teasing. In the teasing step, the molten liquid metal composition is brought into contact with a source of carbon. Carbon reacts with oxygen in the metal composition and forms oxides of carbon, CO+CO ₂ , i.e. gases that exit the molten liquid metal composition and form a reducing atmosphere above the liquid metal bath. The carbon source may be any suitable carbonaceous material, such as any hydrocarbon such as natural gas or liquid hydrocarbon, carbon black, charcoal, coal, or any organic material, including wood. Applicants prefer to use natural gas because of its convenience. Due to the operating conditions under which the composition is molten and liquid, it is easy to create intense contact, and the carbon in the carbon source easily reacts with the oxygen present in the composition, forming oxides of carbon (CO or carbon dioxide), which volatilize as a gas from the molten liquid metal composition. , leaving the metal that was bonded to oxygen in its elemental form. The teasing is preferably performed at a temperature of at least 1150° C. so that the molten liquid bath becomes very fluid and any slag is preferably removed from the liquid metal bath first. The off-gas from the teasing stage is preferably fed to an afterburning stage to convert carbon monoxide to carbon dioxide before it is disposed of. Applicants have found it quite convenient to properly dose the carbon source in order to bring the oxygen content down to the range desired for the anode composition as part of the process of the present invention.

The molten liquid metal composition of the present invention preferably further contains, as part of the impurities, at least one and more preferably all of the following elements at a level that satisfies the respective limit specified for each element:

- at least 0.10 wt.% and/or at most 3.00 wt.% antimony,

- at least 0.010 wt.% and/or at most 0.5 wt.% bismuth,

- at most 6.00 wt.% tin,

- at most 6.00 wt.% lead,

- at least 0.0001 wt.% and at most 0.50 wt.% silver,

- at least 0.005 wt.% and at most 0.40 wt.% arsenic,

- at least 0.001 wt.% and at most 0.100 wt.% sulfur, and

- at most 0.50 wt.% zinc.

In one embodiment, the molten liquid metal composition of the present invention contains sulfur in the specified range, preferably at least 0.005 wt.%, more preferably at least 0.010 wt.%, and optionally at most 0.080 wt.%, preferably at most 0.070 wt. .%, and more preferably at most 0.060 wt.%.

Applicants have found that a limited amount of sulfur can be tolerated in the molten liquid metal composition and that this has the advantage of broadening the feed acceptance criteria for the upstream process, thereby allowing it to accept more sulfur in its feeds. Applicants have also found that it is advantageous to keep the sulfur content of the molten metal composition in line with the upper limit because more sulfur increases the risk of more sulfur being a cathodic impurity and also brings more sulfur into the anode slimes. The latter may be undesirable if the anode slimes are to be further processed through a process that includes a pyrometallurgical step, because the sulfur in the anode slimes can then cause the formation of gaseous sulfur oxides (SO ₂ and/or SO ₃ ).

EXAMPLE

The following example shows one preferred embodiment of the present invention. This example is further illustrated by a figure which shows the flow diagram of the main part of one embodiment of the process of the present invention. In this part of the process, starting from the anode composition 1, cathode product 6, anode sludge product 4, drain product 5 and spent anode product 7 are recovered.

In this figure, the reference numbers mean the following claimed features:

1. Anodes

2. Copper shot

3. Black acid

4. Anode slimes

5. Drain

6. Cathodes

7. Spent anodes

A contaminated molten copper-based liquid metal composition further containing nickel, tin, lead, and other minor metals was prepared according to the process described in our co-pending patent application PCT/EP2018/084384, filed December 11, 2018. This composition is more shown in detail in Table I.

Table I: Contaminated molten liquid metal composition

wt% Cu 92.80 Ni 3.08 sn 1.39 Pb 1.71 Sb 0.65 Ag 0.04 As 0.10 Bi 0.05 Fe 0.02 S 0.02 Zn 0.03 Oxygen 0.10 Total 99.99

This composition further contained about 5 wt. ^ppm gold (Au).

The contaminated molten copper based molten metal composition was introduced into a furnace and brought to a temperature of about 1200° C. by burning natural gas in the furnace. The remaining slag, which floated on the molten metal, was drained. Natural gas was introduced into the liquid metal until the oxygen content of the liquid metal decreased to the range of 20-170 wt. ^ppm .

The oxygen-reduced liquid molten metal was then poured into thin, flat plates constituting the anodes 1 for the subsequent electrorefining step and allowed to cool to ambient temperature.

A total of 52 anodes with an average weight of 444 kg and 51 thick original stainless steel sheets (blanks) were immersed in each of 100 electrolytic cells (200) containing an acidified copper sulfate solution at 68°C as the electrolyte. The average composition of the electrolyte throughout the entire electrolysis cycle is shown in Table II, in grams/liter for the main components and in wt. ^ppm for minor components.

Table II: Average electrolyte composition

grams/liter Cu 39.8 Ni 67.7 sn 0.93

wt. million ^-1 Sb 344.7 As 63.1 Bi 9.0 Fe 403.1 Al 152.5 CD 29.7

The sulfuric acid concentration was maintained at an average concentration of 160 grams/liter by introducing concentrated sulfuric acid (96%) as needed into the leaching tank, further described below. The following process additive addition rates were maintained on average throughout the entire electrolysis cycle by introducing them into the electrolyte inlet to the settling tanks (300):

- Gelatin in the amount of approximately 650 grams / tonne of copper cathode produced,

- HCl in the form of a 30 wt.% solution in an amount of about 430 milliliters / tonne of copper cathode produced,

- HBr in the form of a 48 wt.% solution in an amount of approximately 176 milliliters / tonne of copper cathode produced,

- Flocculant ZETAG® type 7565, cationic polyacrylamide, at approximately 1035 milligrams per ton of copper cathode produced,

- Thiourea at approximately 32 grams per tonne of copper cathode produced.

The average composition of the anodes (stream 1) is shown in Table III.

Table III: Average anode composition

wt% Anodes - 1 Cu 92.90 Ni 3.08 sn 1.39 Pb 1.71 Sb 0.65 Ag 0.04 As 0.10 Bi 0.05 Fe 0.02 S 0.02 Zn 0.03 Oxygen 0.02 Total 100.01

The anodes additionally contained about 5 wt. ^ppm gold (Au).

Anodes (stream 1) and stainless steel blanks were interleaved (120 mm apart) in an electrically parallel arrangement, while the electrolytic cells themselves were connected in series. An average current density of 290 A/m ² was used, which created an average electrical potential between the anodes (positive electrodes) and cathodes (negative electrodes) of 0.46 V.

The passage of an electric current causes the copper to oxidize and go into solution electrochemically. However, some copper will also go into solution in a purely chemical way. All elements (metals) present in the anodes, which are less noble than copper under the given process conditions, also go into solution on the anodes to a certain extent. Electrochemically and chemically dissolved metals other than copper were continuously removed by means of an electrolyte drain stream 5 . This effluent was subjected to an additional purification step (not shown) in which these metals were selectively removed, leaving a purified electrolyte. This prevents the accumulation of impurities in the electrolyte during electrorefining and prevents the co-deposition of impurities on the cathodes. The clean overflow, also referred to as black acid, was recycled to the electrolyte loop as stream 3. The average overflow composition as well as the average black acid composition are shown in Table IV.

Table IV: Average Composition of Plum and Black Acid

wt% Drain
5 black acid
3 Cu 3.32 0.0000 Ni 5.15 0.0930 sn 0.02 0.0000 Pb 0.0013 0.0000 Sb 0.0001 0.0000 Ag 0.0001 0.0000 As 0.0014 0.0390 Bi 0.0000 0.0000 Au 0.0000 0.0000 Fe 0.03 0.0155 Pt 0.0000 0.0000 S 6.57 22.0501 Zn 0.03 0.0000

The copper that had dissolved from the anodes traveled through the electrolyte solution to the cathodes where it coated the original stainless steel sheets to form copper cathodes. The electrolyte was supplied from one front end of the cell. The cell wall with overflow was the side wall perpendicular to the orientation of the electrodes. The electrolyte flow was maintained positive throughout the entire electrolytic cycle. An average renewal rate of approximately 55% cell volume per hour for each cell was used in conjunction with heated air bubbling under the electrodes to prevent anodic passivation. The incoming air was saturated with water vapor at a temperature close to the temperature of the electrolyte before bubbling through a gas diffuser and fed into each cell at an average pressure of 0.75 bar man. All cells were regularly checked during electrorefining for the detection of short-circuited anode/cathode pairs using a gaussmeter mounted on an overhead crane. Short circuits were eliminated by replacing damaged anodes and cathodes or by removing electrodeposited copper nodules that may have formed between shorted anode/cathode pairs. Proper control of all these parameters made it possible to obtain high quality cathodes. The average composition of the cathode (stream 6) is shown in Table V. The cathode deposits produced during electrorefining were clarified and smoothed by the continuous addition of gelatin and thiourea organic additives (stream 8) to the electrolyte just before the pumping system to ensure good mixing.

Table V: Average composition of cathodes

wt% cathodes
6 Cu 99.9761 Ni 0.0025 sn 0.0069 Pb 0.0020 Sb 0.0029 Ag 0.0063 As 0.0007 Bi 0.0001 Au 0.0000 Fe 0.0002 Pt 0.0000 S 0.0016 Zn 0.0001 Total 99.9994

Gold and platinum group metals did not dissolve in the sulphate electrolyte, which means that they did not enter the electrolyte and deposited on the cathode, as can be seen in Table II and Table V. Silver dissolved to some extent from the anodes, but precipitated from the electrolyte as AgCl and AgBr by adding small amounts of HCl and HBr to the electrolyte (stream 8). The appearance of silver in the cathode is considered primarily due to the occlusion of a small amount of anode residues.

Lead and tin formed compounds insoluble in the electrolyte, so these metals almost did not get into the electrolyte. Most of the insoluble impurities from the anodes collected as undissolved sludge at the bottom of the electrolytic cells. These sludges were periodically removed from the cells (200) during the electrorefining operation with a suction head moving over the lower section of the cell provided below the electrodes. Some insoluble impurities were lighter and left the cells through overflows and fell into settling tanks (300). Also, these lighter slurries were periodically removed from the bottom of the settling tanks (400) when these slurries had sufficient time to settle after adding the flocculant to the electrolyte on its way to the settling tank. Thus, all anode slimes were collected in a combined electrolyte stream containing anode slimes and further processed by a filter press (500) which separated the anode slimes (stream 4) from the clear electrolyte. Part of this transparent electrolyte was returned to the circulation tanks (100). The other part of this clear electrolyte was removed as an overflow stream (stream 5) to remove impurities such as copper and nickel by electrowinning so that they do not accumulate in the electrolyte. The anode slimes were washed with hot water at a temperature of 70°C to reduce the amounts of copper and nickel present in dissolved form in the electrolyte. Wash water was returned to the electrorefining process. The average composition of the anode sludge (stream 4) is shown in Table VI. The remainder of the composition is likely to be oxygen and some carbon, most likely derived from organic processing aids.

Table VI: Average composition of anode slimes

wt% Anode slimes - 4 Cu 5.40 Ni 1.87 sn 17.17 Pb 21.21 Sb 8.05 Ag 0.43 As 1.29 Bi 0.62 Fe 0.07 S 6.98 Zn 0.12

The anode sludges were additionally containing about 60 wt. ^ppm gold and about 5 wt. ^ppm platinum.

In order to compensate for electrochemically dissolving impurities on the anodes, which would otherwise cause depletion of copper in the electrolyte, the copper-containing hollow and open pellets (stream 2) obtained from the previous stage of the process were leached (600) in the leaching tank by contacting them with concentrated sulfuric acid used for make-up, the black acid stream returned from the processing of the drain stream, and also with a part of the electrolyte. The liquid product from the leaching vessel was returned to the electrolyte circuit during the electrorefining process. The average composition of the granules used (stream 2) is shown in Table VII. The dissolution of the copper pellets was aided by the introduction of oxygen gas at the bottom of the leaching tank.

Table VII: Average Composition of Copper Granules

wt% Copper granules
2 Cu 95.75 Ni 1.63 sn 0.98 Pb 1.13 Sb 0.31 Ag 0.03 As 0.03 Bi 0.03 Fe 0.01 S 0.02 Zn 0.09

The content of gold and platinum in copper granules was less than 1 wt. ^ppm .

At the end of the anode cycle, each anode was approximately 75% dissolved. Undissolved anode residues (anode waste) were removed as spent anodes (stream 7) from the electrolytic cells, and after washing, weighing and stacking, they were melted and cast into fresh anodes. The average composition of the anodes consumed was apparently the same as the average composition of the anodes shown in Table III.

The above process allowed to work in standard electrolysis cycles of 24 days per cell, that is, 24 days of continuous operation between the introduction of a new set of anodes. The cathodes were taken out approximately every 8 days and replaced by 1/3 during this time, while the electrolysis continued at full current density. The anode slimes were removed from the bottom of the cells at the required frequency, which could vary from once every 3 days to once every 10 days, while the electrolysis was also continued at full current density.

Now, after fully describing this invention, it will be clear to those skilled in the art that the invention can be practiced over a wide range of parameters within the scope of what is claimed without departing from the scope of the invention as defined by the claims.

Claims (54)

1. A method for producing electrorefined copper by electrolysis, including electrorefining of metallic copper in an electrolytic cell from at least one copper anode to at least one copper cathode using an electrolyte based on sulfuric acid, characterized in that electrorefining of metallic copper in an electrolytic cell is carried out at a difference potentials between the anode and the cathode is less than 1.6 V, and the anode contains at most 98.0 wt. % copper and less than 1.00 wt. % iron, the current density through the cell is at least 180 A/m ² of the cathode surface, while during the electrorefining operation, the electrolyte is removed from the electrolytic cell with an average electrolyte renewal rate of at least 30% and at most 1900% per hour, and at least partially, the electrolyte is removed by pouring the first stream of electrolyte through at least one wall of the cell, introducing gas into the electrolytic cell, and bubbling gas through the electrolyte in the gap between the anode and cathode. 2. The method according to claim 1, wherein at least a portion of the anode sludge contained in the electrolytic cell is removed from the electrolytic cell with the first electrolyte stream. 3. The method according to claim 1 or 2, wherein the first electrolyte stream is passed through at least one settling tank with a sufficiently high residence time at a sufficiently low liquid velocity for the anode sludge to settle to the bottom of the settling tank. 4. The method of claim 3, wherein a third electrolyte stream containing anode slimes is removed from the bottom of the settler. 5. The method according to any one of paragraphs. 1-4, in which a second electrolyte stream containing anode slimes is removed from the bottom of the electrolytic cell. 6. The method according to any one of paragraphs. 1-5 which includes recycling to the electrolytic cell the electrolyte that has been removed from the electrolytic cell. 7. The method of claim. 6, which includes the removal of the drain stream of electrolyte from the recirculating electrolyte to control the concentration of accumulated compounds in the electrolyte. 8. The method according to any one of paragraphs. 1-7 in which additional copper cations are introduced into the electrolyte in the electrolytic cell. 9. The method according to any one of paragraphs. 1-8, in which the gas that is introduced into the electrolytic cell is air. 10. The method according to any one of paragraphs. 1-9, in which the gas is introduced into the electrolytic cell through a gas diffuser provided below the electrodes and above the space provided at the bottom of the electrolytic cell to collect the layer of anode sludge, and preferably the gas diffuser comprises selectively perforated diffuser tubes connected to the gas supply pipe. 11. The method according to any one of paragraphs. 1-10, in which the composition of the anode meets at least one, and preferably all of the following conditions: contains Nickel in the range from 0.25 wt. % up to 10.0 wt. %, contains lead in the range of 0.25 wt. % up to 6.00 wt. %, contains tin in the range from 0.25 wt. % up to 6.00 wt. %, contains antimony in the range from 0.10 wt. % up to 3.00 wt. %, contains bismuth in the range from 0.010 wt. % up to 0.50 wt. %, contains at least 0.0001 wt. % iron, contains zinc in the range from 0.0010 wt. % up to 0.50 wt. %, contains arsenic in the range from 0.005 wt. % up to 0.40 wt. %, contains silver in the range from 0.0001 wt. % up to 0.50 wt. % And contains oxygen in the range from 5 wt. ^ppm to 500 wt. ^ppm . 12. The method according to any one of paragraphs. 1-11, in which the anode is obtained from a molten liquid metal composition containing at least 90.10 wt. % and at most 97 wt. % copper, the rest - other elements as impurities, some of which are: at least 0.1 wt. % nickel, at least 0.0001 wt. % and less than 1.00 wt. % iron, at least 250 wt. ^ppm and at most 3000 wt. ^ppm oxygen. 13. The method of claim 12, wherein the molten liquid metal composition contains, as part of the impurities, at least one, and more preferably all of the following: at least 0.10 wt. % and at most 3.00 wt. % antimony, at least 0.010 wt. % and at most 0.50 wt. % bismuth, at most 6.00 wt. % tin, at most 6.00 wt. % lead at least 0.0001 wt. % and at most 0.50 wt. % silver, at least 0.005 wt. % and at most 0.40 wt. % arsenic, at least 0.001 wt. % and at most 0.100 wt. % sulfur and at most 0.50 wt. % zinc. 14. The method according to any one of paragraphs. 1-13, in which the electrolyte contains at least one, and preferably all of the following components: copper in the range of 20-55 grams/liter, nickel in the range of 25-90 grams/litre, sulfuric acid in the range of 130-200 grams/litre, tin in the range of 0.4-1.4 grams/liter and arsenic in the range of 10·10 ^-3 - 200·10 ^-3 grams/liter. 15. Molten liquid metal composition suitable for casting anodes for carrying out the method according to any one of paragraphs. 1-14, and the composition contains at least 90.10 wt. % and at most 97 wt. % copper, the rest - other elements as impurities, some of which are at least 0.1 wt. % nickel, at least 0.0001 wt. % and less than 1.00 wt. % iron and at least 250 wt. ^ppm and at most 3000 wt. ^ppm oxygen. 16. A molten liquid metal composition according to claim 15, which contains, as another part of the impurities, at least one, and more preferably all of the following elements: at least 0.10 wt. % and at most 3.00 wt. % antimony, at least 0.010 wt. % and at most 0.50 wt. % bismuth, at most 6.00 wt. % tin, at most 6.00 wt. % lead at least 0.0001 wt. % and at most 0.50 wt. % silver, at least 0.005 wt. % and at most 0.40 wt. % arsenic, at least 0.001 wt. % and at most 0.100 wt. % sulfur and at most 0.50 wt. % zinc. 17. The molten liquid metal composition according to claim 15 or 16, which has an oxygen content reduced to a value that provides a range of its concentration in the composition of the said anode from 5 wt. ^ppm to 500 wt. ^ppm .

Images