EP2783026A1 - A method for industrial copper electrorefining - Google Patents

Abstract

A method of copper electrorefining is disclosed. The method includes arranging at least one anode of copper material to be refined in contact with an electrolyte solution and arranging at least one cathode in contact with the electrolyte solution. The anode and cathode are connected electrically to an electrical source, and the source is operated under potential controlled conditions. The electrical potential at the cathode is -0.30 V to -0.55 V with respect to the copper material at the anode, thereby causing the deposition of electrorefined copper at the cathode. The method also includes potentiostatic pulse electrolysis (PPE) and periodic potential reversal (PPR) in order to produce a copper deposit having a controllable structure, for example in terms of roughness or porosity. An apparatus for performing potential controlled electrolysis is also disclosed.

Description

A Method for Industrial Copper Electrorefining

Field of the Invention

The invention pertains to a new method for copper electrorefining using electrical potential control, which has application in the copper industry.

Background to the Invention

According to the statistical data given in the patent application No PL396693, the annual global production of electrolytic copper obtained by copper electrorefining processes reached 15 000 000 tons in 2009. Furthermore, from the data presented in the monograph by W.G. Davenport, M. King & M. Schlesinger, entitled "Extractive Metallurgy of Copper", published by Elsevier Science Ltd. Oxford in 2002, it is known that high purity copper with a copper concentration of above 99.90% is obtainable as a result of electrorefining. Both the copper quality and the copper market price depend on its mechanical, electrical and thermal properties which change depending on the impurities content. An electrorefining method allows the removal of impurities from copper which cannot be removed by the alternative process of fire-refining. It also allows the recovery of other precious metals such as gold, silver, platinum, nickel and selenium.

In the known process an anode made of impure copper obtained during a fire refining process or from other sources such as recycling, scrap etc. is subjected to electrorefining. During an anodic process, copper is dissolved and aqueous solution is obtained according to the following basic reaction (although in practice the reaction is rather more complex): anode: Cu ⁰ = Cu²⁺ + 2e

A sheet of pure copper or acid-resistant steel (stainless steel) provides the cathode on which metallic copper is deposited according to the following basic reaction: cathode: Cu ²⁺ + 2e = Cu°

Examples of electrorefining process conditions in the industrial environment of the KGHM Polish Copper Glogow Copper Smelter and Refinery are presented in a PhD thesis by Olimpia Gladysz, University of Wroclaw Chemistry Department 2006. According to the above-mentioned source, impure copper sheets (sheets of copper smelted using fire refining process, having a size of 1 x 1 x 0.05m) undergo dissolution as the anode in the electrorefining process. A pure copper sheet (obtained using the electrolytic method, the thickness of which is in the range from 0.001 -0.003 m) on which metallic copper is deposited, serves as a cathode. The anodes are hung in electrolytic tanks filled with an electrolyte consisting of copper ions, sulphuric acid, organic additives and chloride ions. A typical electrolyte composition is presented in Table 1 . Concrete tanks covered with lead, as well as newer ones made of resin concrete reinforced with glass fiber bars, are used to contain the electrolyte. As opposed to concrete tanks the resin ones are resistant to sulphuric acid. They are also dielectrics and good heat insulators. Cathodic "pads" in the form of sheets are hung between the anodes and connected to the current source. There are from thirty to sixty pairs of anodes and cathodes connected in parallel in each tank.

Table 1 . Electrolyte composition and basic copper electrorefining conditions in KGHM Polish Copper Glogow Copper Smelter and Refinery.

According to the same reference source, a continuous, laminar electrolyte flow through the tanks (about 0.02 m³/min) at constant temperature and flow pressure is the condition required to conduct a proper electrorefining process. The electrolyte flow speed is usually in the range from 0.01 -0.03 m³/min which enables a full electrolyte replacement every 4 to 6 hours. In order to do this specialised equipment is used: acid-resistant pumps, heaters, polyethylene tissue covering the tanks. Maintaining an appropriately high temperature (60- 65°C) is also highly significant in the electrorefining process. During the electrorefining process, ions of such impurities as As, Bi, Co, Fe, Ni and Sb constantly dissolve into the solution from the anode. It is thought that for the electrorefining process to be conducted properly the concentration of these elements in the post-refining electrolyte should not exceed the following values: As - 20 g/dm³, Bi - 0.6 g/ dm³, Fe - 2 g/dm³, Ni - 25 g/dm³ and Sb - 0.7 g/dm³. In order to decrease the concentration of the impurities, impure refining electrolyte should be removed and replaced with sulphuric acid. In the 1990s new systems of copper electrorefining were put into operation - the ISA SYSTEM was introduced at a number of locations (Townsville - Australia, Copper Range Co. - USA, Norddeutsche - Germany), together with the KIDD SYSTEM (Kidd Creek - Canada). In these systems the electrorefining is conducted on multi-use cathodes made of acid- resistant steel that boasts durability of 20 years and more. The copper layer deposited in a 5-8 day cycle is removed mechanically and the cathodes are returned to the tanks. The metallic copper obtained using this system is of higher quality in spite of using higher current densities reaching up to 340 A/m². The current efficiency of both processes is comparable and is in the range from 95% to 97%. The difference of potentials between the anode and the cathode is also comparable and equals about 0.3 V. Advantageous effects influencing the quality are achieved by the following factors: shorter time of cathode deposition growth in tanks, the electrodes are hung vertically with exact precision, minimum number of short-circuits as well as automation of a conducted process control and parameter adjustment. A system of permanent acid-resistant cathodes does not require preparation of cathode pads which reduces the production costs. At present, the majority of newly-built and modernized refineries are constructed using this system. According to the above-presented data, which is representative of industry practice, the copper electrorefining process is carried out in galvanostatic conditions (constant current conditions). This means that the process is conducted at a "forced" speed/velocity of copper deposition, i.e. at constant current density. It should be added, however, that the current density on individual cathodes in industrial tanks can vary significantly which influences the quality of the obtained copper. Cathode current density is the most important economic parameter of the copper electrorefining process. Most research work devoted to electrorefining processes concerns the improvement of cathodic deposition quality and purity. It concentrates especially on how to avoid the formation of dendrites on the cathode which may cause short-circuits between the anode and cathode thereby preserving the highest possible cathode current density. Research on how to avoid passivation and corrosion pits has also been undertaken. For reasons of economy, copper electrorefining processes should proceed at the highest current density whilst maintaining an appropriate (fine-crystalline) structure and chemical composition of the cathode. The ISA technology that is used nowadays allows the highest possible current densities of the galvanostatic or "current controlled" electrolysis processes to be realised. Nevertheless, there is an ongoing need to develop electrorefining techniques in the copper industry, in order to produce a high quality copper product at lower costs. It is in the context of addressing these problems that the present invention has been devised.

Summary of the Invention

In accordance with a first aspect of the invention we provide a method of industrial copper electrorefining comprising, arranging at least one anode of copper material to be refined in contact with an electrolyte solution; arranging at least one cathode in contact with the electrolyte solution; electrically connecting the anode and cathode to an electrical source, and operating the electrical source under electrical potential controlled conditions such that during at least part of the application of the said conditions, the electrical potential at the cathode is -0.30 V to -0.55 V with respect to the copper material at the anode, thereby causing the deposition of electrorefined copper at the cathode.

We have realized that, unexpectedly and in complete contrast with industrial practice, significant benefits may be derived by the use of electrical potential controlled conditions during the industrial electrorefining of copper.

In accordance with a second aspect of the invention we provide an industrial copper electrorefining system comprising:

a container for retaining an industrial electrolyte;

at least one first electrode formed from copper material to be refined and being positioned within use in contact with the industrial electrolyte with the container; at least one second electrode positioned within use in contact within the industrial electrolyte within the container; and,

a power supply operable under electrical potential controlled conditions and connected electrically when in use to each of the said at least one first and at least one second electrodes, such that during at least part of the application of the said conditions, the electrical potential at the at least one second electrode is -0.30 V to -0.55 V with respect to the copper material at the at least one first electrode, thereby causing the deposition of electrorefined copper at the at least one second electrode.

Typically the apparatus according to the second aspect is adapted to perform the method according to the first aspect of the invention.

As explained above, the Cu industry presently conducts copper electrorefining processes using current control. It will be appreciated that, under small scale laboratory conditions, in principle any electrolysis can be carried out either in current control mode or potential control mode. Electrochemical processes are often classified in accordance to the output signal of the potentiostat, galvanostat or rectifier used. Furthermore, the dc current and ac current electrochemical processes are then distinguished. In special cases where the applied signal has a rectangular shape (waveform) the electrochemical processes are called "galvanostatic" or "potentiostatic" when constant current or potential is applied to the electrodes, respectively. However, it is well known that, particularly in an industrial environment, the current distribution at the electrorefining electrodes is not uniform and may vary by even more than 50% of the average current density depending on the site of the cathode. Additionally, current densities vary between cathodes in one multi-electrode electrolysis cell. Consequently, in the present description apart from those widely used terms we use the more general terms of "complex form current" (CFC) and "complex form potential" (CFP). These terms describe (according to Boyko F.K. and Ptitsyna Ye.V., Industrial power engineering - 2 (1996) pp. 23-26) all types of applied signals at the electrodes including such signals with or without a constant component, a current of adjustable frequency, periodic current reversal (PCR) or pulse electrolysis (PE) (with various amplitudes, pulse ratio and duration of impulses), as a variation of a complex form current and potential. Preferably therefore, when implementing the present invention, the electrical potential controlled conditions include the application of complex form potential.

When current is controlled the electrode potential cannot be controlled but changes with time (and at points in space such as at the electrode/electrolyte interface) according to the particular electrochemical processes mechanism and kinetics (e.g. charge transfer, chemical reactions of electroactive species, diffusion of electroactive species). When the electrical potential is applied in a controlled manner the current is not controlled but changes with time according to the electrochemical processes mechanism and kinetics. Such electrical potential is applied by a power supply which ensures that the potential applied is substantially independent of the current drawn from the power supply (within normal operational limits of the apparatus).

These are two fundamentally different processes because current (or more precisely current density) is a measure of the rate of the electrochemical processes. In contrast, electrical potential is a driving force of the electrochemical processes related directly to such notions as for example free enthalpy of the electrochemical reaction.

When controlled current is applied the processes proceed with a well-defined rate (however there is no control of the electrode reactions). It is for this reason that current control has been used exclusively in the industrial electrorefining of copper. When a controlled potential is applied the electrode process is well defined e.g. electrodeposition of copper ions but its rate varies according to the conditions (temperature, copper concentrations etc.) of the process. In potential controlled electrolysis the product should be purer than in the case of current controlled conditions because, as is described in Modern Electroplating, Fifth Edition, Edited by Mordechay Schlesinger and Milan Paunovic, 2010 John Wiley & Sons, Inc. p. 6: "If an external current greater than the limiting current i_L is forced through the electrode, the double layer is further charged and the potential of the electrode will change until some other process, other than reduction of M^z+, can occur".

Consequently, in the case of industrial copper electrolysis using current control, other processes can occur such as decomposition of water i.e. hydrogen evolution reaction as a consequence of varying potential. On the other hand, using the new, potential controlled processes described in the present invention the potential of the cathode is controlled and chosen in such a way that the only process to occur is copper electrodeposition. This way the purer cathodic copper with higher current efficiencies may be obtained.

It must be understood that present industrial electrorefining processes, where current control electrolysis is used, are carried out at a fraction of the maximum cathodic current density which it is possible to obtain in certain conditions i.e. copper ions concentration, temperature, electrolyte flow etc. The maximum current density is called the "limiting current density" and according to A. Filzwieser, K. Hein, and G. Mori, JOM, 2002 April pp. 28 - 31 may reach, at natural convection conditions, even 2000 A m², although the value of i_L cited for industrial conditions is around 800 A m². In the present industrial refineries a cathodic current density of only up to 350 A/m² is used. That implies that the rate of the industrial copper electrorefining is an activation (charge transfer) controlled process. The activation control is often cited as a required condition for the industrial electrorefining. Crucially, the reason for using such low cathodic current densities in the galvanostatic (or more general current control) industrial electrorefining as cited above is that in the currently used refineries the increase in current density results in creation of nodular and dendritic structures at the cathode and finally, at current densities close to the limiting current densities, a copper powder is produced. These are all features which decrease the quality of the cathodic copper and decrease the current efficiency of the copper electrorefining process. One of the major problems of the copper electrorefining is short- circuiting between anode and cathode due to the growth of dendrites on the cathode.

We have found that all of these phenomena are avoided when a potential controlled process is used. This process can be carried out at the limiting current density (e.g. under natural convection conditions) with very high current efficiencies, producing very smooth, fine-crystallite structures, with very high purity copper (higher than 99.95wt%, more preferably higher than 99.99wt%) deposited at the cathode. Consequently, in complete contrast to the presently held belief in the industry, according to the present invention and especially as demonstrated in the examples discussed below, copper electrorefining can be carried out at diffusion limiting conditions by using electrical potential control.

The use of potential controlled electrorefining allows the application of more negative cathodic potentials than are found in known refineries (under current control). Whilst the potentials applied may lie in the range of -0.30V to -0.55V, preferably the range used is - 0.35V to -0.55V, more preferably -0.40V to -0.55 V. In contrast, present refineries use potentials of around -0.3V.

The process of potentiostatic copper deposition has been largely ignored in applied electrochemistry research. In the majority of cases the use of potentiostatic control has been confined to the process of electrowinning (note, not electrorefining), as presented in the work by I. Giannopoulou and D.Panias published in 2007 (Minerals Engineering 20 (2007) 753-760) in which the results of research are presented on selective copper and other metals deposition from synthetic solutions simulating industrial electrolyte from Bor in Serbia containing about 6 g/dm³ Cu, 0.6 g/dm³ Ni and 0.5 g/dm³ As, as well as trace quantities of other metals such as Sn, Bi, Sb, Pb, Fe.

The studies have been carried out on the copper cathode, with the anode formed from a titanium net covered with platinum. The results of the studies have shown that copper can be deposited in the electrolytic process in the form of impure cathodes. The main impurity of copper deposited on the cathode is arsenic which reacts with copper and creates copper arsenide as well as bismuth and antimony.

A novel process of potentiostatic copper electrowinning has been presented in Polish patent application number PL396693. Moreover, a range of potentials which allow the obtaining of copper powders in the process of electrodeposition from industrial electrolytes used in the copper industry has been determined in papers by A. tukomska, A. Plewka P. Los published in 2009 (Journal of Electroanalytical Chemistry 633(2009)92; 637(2009)50) as well as in PCT patent application number PCT/PL2010/000022. Electrowinning is an entirely different concept with a separate aim to electrorefining. There is still the need to provide an industrial electrorefining method in order to achieve higher cathode current densities while maintaining high (commercial) copper purity and its fine- crystalline structure. Unexpectedly the above-mentioned problems related to current controlled industrial electrorefining have been solved by the present invention.

Advantageously, the process parameters used in implementing the invention are very close to those currently used in industrial electrorefining, especially the same basic substrates i.e. electrolytes and anodes are used in a new potential-controlled electrorefining process. The advantage of the new process is in that by controlling the cathode potential the limiting current of the process can be reached and, according to the above given exemplary limiting current densities, the cathodic current density can be approximately 3 to 5 times higher than in the current controlled (e.g. galvanostatic) electrorefining process. This is a huge commercial advantage because the cathodic copper manufacturing will be 3 to 5 times faster than it is currently which may result in the substantial increase of the existing copper refineries' production capacity and/or in the decrease in the costs of manufacturing each 1 kg of copper. As discussed above, a new potential-controlled electrorefining process will result in higher current efficiencies and better purity of greater than 99.95%, and more preferably greater than 99.99% - both are related with the more selective nature of the cathode potential controlled electrolysis which result practically in the absence of competitive electrochemical cathodic processes. Unlike in the case of current controlled processes presently used in the industry, the high current density potential controlled process gives a compact copper layer of fine-crystalline structure free of nodules and dendrites. This is a very important advantage of the invention because any modification of existing copper process technology is likely to be extremely expensive. For instance if there is a need to use a different electrolyte or/and electrodes then this is very expensive and complicated to implement on a commercial scale.

According to Beukes, NT. and Badenhorst, J. Copper electrowinning: theoretical and practical design. Hydrometallurgy Conference 2009, The Southern African Institute of Mining and Metallurgy, 2009, pp. 213-240 there are three main ways to increase cathodic current density in the existing (current controlled process) copper refineries:

• Optimizing the cell design

• Employing various types of forced convection

· Periodic current reversal

This publication demonstrates the present developmental aims within the art and it is notable that there is no consideration of departing from current controlled processes. The new potential controlled copper electrorefining process according to the present invention does not require "optimizing cell designs" nor "employing various types of forced convection" to obtain very high cathodic current densities and very good quality and purity copper. Another important advantage of potential controlled electrolysis is related to the fact that application of more cathodic potentials minimizes the process of deposited copper oxidation by iron (III) ions and in consequence this may decrease the concentration of iron in the cathodic copper as well as improve the current efficiency of the electrorefining process.

The most important advantage of the potential controlled electrorefining process in comparison with the copper electrowinning process is that copper anodic dissolution proceeds with a negligible polarization (overpotential) of approximately 10 mV. This ₁ Q

way the cathodic potential is very precisely controlled in the electrorefining process. A very high overpotential and complexity of the anodic processes make potential control in the electrowinning process much more difficult to implement on an industrial scale. Whilst a constant electrical potential may be applied during the electrorefining, it is also contemplated that one or more of the magnitude and polarity of the electrical potential are modulated. Such modulation provides control over the resultant structure of the deposited copper.

For example the electrical potential may be modulated as a rectangular waveform having a magnitude of the electrical potential at the cathode of between -0.30 V and -0.55 V. Furthermore, potentiostatic pulse electrolysis (PPE) conditions may be applied in which, for example, a number of cathodic pulses in the range 3 to 300 are applied, each having a substantially constant potential in the range -0.30V to -0.55V with reference to the copper material at the anode, and each having a duration of between 5 and 18000 seconds, wherein the pulses are separated in time by open circuit breaks, each having a duration in the range 0.1 to 100 seconds. It is also contemplated that periodic potential reversal (PPR) conditions are applied in which a cathodic pulse having a potential in the range -0.30 V to - 0.55 V, with reference to copper material anode is applied for a duration in the range 5 to 18 000 seconds, the cathodic pulse being followed by an anodic pulse in the range of +0.05 V to +0.60 V, with reference to the copper material anode, whereby the duration of the anodic pulse is shorter than the cathodic pulse by at least 50% and wherein the sequence formed from the cathodic pulse and anodic pulse is repeated from 3 to 30 times. It is noted here that multiple pulses (possibly of different magnitudes and durations) may be applied before any later potential reversal during any particular sequence.

In some applications it may be advantageous to apply periodic potential reversal (PPR) conditions in which a cathodic pulse having a potential in the range -0.30 V to -0.55 V, with reference to copper material anode is applied for a duration in the range 5 to 18 000 seconds, the cathodic pulse being followed by an anodic pulse in the range of +0.05 V to +0.60 V, with reference to the copper material anode, whereby the duration of the anodic pulse is shorter than the cathodic pulse and wherein open circuit conditions are applied for a period between the cathodic and anodic pulses and the sequence formed from the cathodic pulse and anodic pulse is repeated from 3 to 30 times. Typically in this case the said open circuit conditions are applied twice during the sequence as the potential is reversed, that is between a transition from cathodic to anodic conditions and from anodic to cathodic conditions.

Advantageously, in the method according to the invention the electrolyte used in the electrorefining process typically comprises 90 g/dm³ to 200 g/dm³ H₂S0₄ and 1 g/dm³ to 50 g/dm³ Cu as well as other typical components of such solutions. A very important advantage of the potential controlled process is the possibility of carrying out the electrorefining at a very wide range of copper ion concentrations, including less than 40 g/dm³. In contrast, current industrial processes require copper (II) ion concentrations of not less than around 40 g/dm³. It is important to note that a cathode potential controlled copper electrorefining process enables the best exploitation of natural convection. As was pointed out in Russian Journal of Electrochemistry 6 (2004) 723-729 and Russian Journal of Electrochemistry 4 (2008) 459-469 in the conditions of natural convection (or slow electrolyte flow) the presence of additional, different than copper(ll) sulphate (which is an electroactive species), electrolyte components (which are not electroactive species in the electrorefining process) is advantageous because it influences the thickness of the diffusion layer and consequently causes the increase of the limiting current. This view is supported by the results presented in A. tukomska, A. Plewka and P. Los, Journal of Electroanalytical Chemistry 633 (2009) 92-98 where such influence is found on the steady-state currents registered in industrial solutions (complex composition) and sulphuric acid and copper (II) sulphate only solutions at the ultramicroelectrodes under conditions in which the lowest temperatures and potentials applied to the cathode are used. It confirms that surface phenomena do not play an important role in potentiostatic electrolysis at high potentials and temperatures. Consequently, the presence of other components other than sulphuric acid and copper (II) sulphate is an advantage in the new, potential controlled process. Another important advantage is that the potential controlled process does not require the addition of organic additives. Such additives are used in current controlled processes to control the structure of the deposited copper. Preferably therefore the electrolyte is substantially free of such additives includes animal glue and/or thiourea. This means that there is no detectable level of such additives in the electrolyte.

Typically the preferred arrangement of the electrodes (anode and cathode) is such that their spatial separation is 5cm or less in an industrial cell. In this case it is preferred also that the electrodes are provided as substantially planar structures (such as sheets) arranged in parallel with the above given separation distance. It is also advantageous that, in the method, typically the process of potentiostatic copper electrorefining is carried out at temperatures ranging from 18°C to 65°C, advantageously from 18°C to 30°C. Therefore there is no need to heat the electrolyte additionally as in the currently used methods. This is another important advantage since current electrorefining technology does not permit the use of the process at temperatures lower than approximately 50°C. As is shown below the new potentiostatic process can be carried out in industrial electrolytes at temperatures as low as 20°C with cathodic current densities comparable with the present industrial electrorefining process at 60°C. Consequently, the new potential controlled electrorefining can be carried out using simplified installations and with huge energy savings in comparison with current processes.

It is also advantageous that, with the new method, typically the process of potentiostatic electrorefining is conducted using a cathode made of stainless steel or copper. Furthermore, the copper material of the anode may be formed from a fire-refined, scrap or recycled copper material.

It is advantageous that the process of potentiostatic electrorefining is carried out using an electrolyte which circulates continually, is stirred or otherwise agitated. Consequently, the new, potential controlled copper electrorefining can be carried out in both traditional and ISA installations currently used in the electrorefining. An electrolyte management system may perform one or more of filtering, removing impurities, adding other agents (such as sulphuric acid), agitating/circulating/stirring and temperature control of the electrolyte.

In summary, the present invention has a great advantage over the above-described prior art methods because the method of cathode potential controlled copper electrorefining allows the achievement of significantly higher cathode current densities (increasing the production volume) while maintaining high (commercial level) copper purity and a fine- crystalline structure. Typically, the process of cathode potential controlled electrorefining according to the invention has a number of advantageous characteristics, including:

- in the process of potentiostatic electrorefining, the electrolyte may have a similar (although not identical) ionic composition as used currently in the galvanostatic process;

- the process can be carried out at high current densities up to about 2000 A m² at the temperature of 60°C and 500 A m² at room temperature (about 20°C). By way of contrast it will be understood that using current densities of such magnitude in a galvanostatic electrorefining process causes a drastic deterioration in cathode copper quality;

- the purity of cathodic copper obtained in the process of potential controlled electrolysis may be greater than 99.99%; - the "current efficiency" of the potentiostatic electrorefining process may be higher than 97%.

Brief Description of the Drawings

Some examples of a method of electrorefining according to the invention are now described with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of apparatus used in association with the examples; Figure 2 is a flow diagram providing a general overview of the method;

Figure 3a shows a potential pulse electrolysis waveform having pulses each of which have a constant magnitude;

Figure 3b shows potential pulse electrolysis waveforms having pulses of constant magnitude other than an initial pulse;

Figure 3c shows an applied potential waveform including periodic potential reversal; and Figure 3d shows an applied potential waveform including periodic potential reversal and intervening periods of open circuit conditions.

Description of Preferred Examples

A schematic view of industrial apparatus suitable for performing the present invention is illustrated in Figure 1 . Here, a tank 1 is provided, for simplicity this being illustrated as a single container. In practice this is formed from a number of individual cells formed from a polymer material which exhibits good long term resistance to the electrolyte. The electrolyte is illustrated at 2 and has a composition described in more detail in association with the examples below. First electrodes 3 (shown as solid lines) are provided, formed from copper material to be refined and are arranged to form the anodes within the cells. These take the form of planar sheets and are spaced at regular intervals, hanging vertically within the electrolyte 2. Second electrodes 4 (dashed lines) are provided taking a similar form to the first electrodes, again hung vertically, although in this case being formed from either previously electrorefined copper or stainless steel. The second electrodes form the cathodes within each cell and are positioned equally spaced between the anodes, for example at a distance of a few centimetres from the anodes. The anodes and adjacent cathodes may be thought of as "pairs" for gaining an understanding of the apparatus. A potential controlled power supply 5 is provided to drive the electrorefining process. Each anode is connected electrically to the power supply via a supply line 6; similarly each cathode is also connected electrically by a supply line 7. An electrolyte system 8 is illustrated. This performs a number of functions including filtering the electrolyte, controlling its composition (by the addition and removal of impurities/agents), maintaining the electrolyte at a predetermined temperature and ensuring the circulation of the electrolyte within the cells. The apparatus is controlled by a controller 9 which is in communication with the electrolyte system 8 and power supply 5.

Figure 2 illustrates a general overview of the process. At step 100 the anodes 3 are manufactured from a material which it is desired to be refined. At step 200 clean cathodes 4 are obtained (these may have been used in a previous electrorefining cycle). At step 300 the anodes and cathodes are arranged in their cells within the tank 1 and are connected electrically to the power supply 5. The electrolyte 2 is then introduced into the tank and the electrolyte system 8 is operated by the controller 9 so as to establish a flow of electrolyte within the cells at the appropriate temperature, which may be room temperature. At step 500, the controller 9 operates the power supply 5 so as to deliver electrical potential controlled conditions. Monitoring of the process conditions (including the current and potential in each cell) is performed throughout the process by the controller 9. Once the process has stabilized the refining proceeds at step 600. This may involve the application of a constant potential, although optionally a pulsed electrorefining and/or periodic potential reversal may be applied (to be described in association with the examples below). This process continues for an extensive period (which may be hours or days) until a sufficient amount of anode material has been refined. Once this point is reached, at step 700 the electrical power supply is terminated, the eroded anodes are removed (unless they contain sufficient material for reuse) and the cathodes (containing the refined copper) are washed. At step 800, the cleaned cathodes are then subjected to mechanical removal of the high purity copper which has been deposited.

A number of examples are now described which may be implemented industrially according to the general apparatus and method identified above. These examples are described in terms of experiments performed using apparatus which is analogous to industrial refining apparatus.

Example 1

A pair of electrodes is provided in an electrochemical tank made from polyvinylchloride. The cathode is made from stainless steel sheet the thickness of which is 0.1 mm and 2 cm² of surface area. The anode (reference electrode) is made from 0.25 mm thick copper sheet, the surface of which has an area of 100 cm². The process is conducted at room temperature (about 20°C). The tank is filled with an electrolyte of the following composition: 46 g/dm³ Cu, 180 g/dm³ H₂S0₄ and 0.1 g/dm³ Fe, 0.3 g/dm³ Sb, 0.03 g/dm³ Bi, 5 g/dm³ Ni, 10 g/dm³ As, 0.00015 g/dm³ Ag, 0.001 g/dm³ Ba, 0.4 g/dm³ Ca, 0.001 g/dm³ Cd, 0.03 g/dm³ Co, 0.02 g/dm³ Mg, 0.0004 g/dm³ Mn, 0.007 g/dm³ Pb and 0.001 g/dm³ Pd. The electrolyte composition resembles a typical industrial electrorefining electrolyte as for example used in a prior art copper electrorefining process at the KGHM PM copper works (discussed earlier). However, organic additives are not included within the electrolyte. In the prior art industrial electrolytes the usual additives such as thiourea and animal glue undergo hydrolysis, so after only a few days only their hydrolysis products are present in the solution. According to the discussion presented above the new method should be tested in the electrolyte containing non-electroactive components since their presence influences the rate of the mass transport of copper (II) ions to the cathode and consequently the value of the limiting current. Additionally the experimental tests should be carried out in complex composition electrolytes since they influence the ionic force of the electrolyte and consequently the activity coefficient of copper (II) ions. From the theory it is known that the driving force of the diffusion is a gradient of activities. Each electrode is connected with the aid of a special cable to a commercially available rectifier which can be used to programme the duration of the potentiostatic electrolysis process from 1 minute to several days and which provides currents of up to 500 A flowing from the rectifier to/from the electrodes. The current changes depending on the duration of the electrolysis are measured during the process. The solution is not stirred in this case. Parameters of potentiostatic electrolysis used:

Stainless steel cathode potential with reference to copper anode E= -0.300 V;

Electrolysis time t = 1 h;

Stationary current density of approximately 300 A/m² at the cathode is achieved after a constant potential of -0.300 V is applied to the electrodes for about 25 seconds.

After having deposited copper on the stainless steel cathode, the cathode deposit is removed from the cathode mechanically, washed with water, air-dried and the composition of the obtained copper is studied using an EDS/EDX method. It is found that the obtained cathode deposit has a fine crystalline structure without dendrites. Oxygen makes up about 0.05% of the weight and is the only impurity present in the obtained cathode copper. So the obtained cathode copper has a purity higher than 99.95%. Having compared the deposited copper mass with the theoretical mass of copper that should be deposited (using Faraday's law), it is found that the current efficiency of the process is higher than 97%. This examples uses a similar potential magnitude as found in many known industrial (current controlled) prior art refining processes.

Example 2 In this second example the experimental set-up and electrolysis conditions are similar to those in Example 1 except that a different cathode potential is used, causing a higher current.

Parameters of potentiostatic electrolysis:

Stainless steel cathode potential with reference to copper anode E= -0.450 V;

Electrolysis time t = 1 h;

Stationary current density of approximately 500 A m² at the cathode is achieved after constant potential -0.450 V has been applied to the electrodes for about 25 seconds. After having deposited copper on the stainless steel cathode, the cathode deposit is removed from the cathode mechanically, washed with water, air-dried and the composition of the obtained copper is studied using an EDS/EDX method. Again, as for Example 1 , it is found that the obtained cathode deposit has a fine-crystalline structure without dendrites. Oxygen makes up about 0.05% of the weight and is the only/sole impurity present in the obtained cathode copper. So the obtained cathode copper has a purity higher than 99.95%. Having compared the deposited copper mass with the theoretical mass of copper that should be deposited using Faraday's law, it is found that the current efficiency of the process is higher than 97%. Hence it is observed that a high quality Cu deposit in terms of purity and structure is obtainable at current densities that exceed those observed in prior art industrial processes, despite using an ambient temperature process, by the use of a mode cathodic voltage under potential control.

Example 3

The experimental set-up and electrolysis conditions are the same as in Example 2 except the process is performed at an elevated temperature of 60°C. Parameters of potentiostatic electrolysis:

Stainless steel cathode potential with reference to copper anode E= -0.450 V;

Electrolysis time t = 1 h;

Stationary current density of approximately 1400 A m² at the cathode is achieved after constant potential -0.450 V had been applied to the electrodes for about 25 seconds.

After having deposited copper on the steel cathode, the cathode deposit is removed from the cathode mechanically, washed with water, air-dried and the composition of the obtained copper is studied using an EDS/EDX method. It is found that the obtained cathode deposit has a fine-crystalline structure without dendrites. Oxygen makes up about 0.05% of weight and is the only/sole impurity present in the obtained cathode copper. So the obtained cathode copper has the purity higher than 99.95%. Having compared the deposited copper mass with the theoretical mass of copper that is deposited using Faraday's law, it is found that the current efficiency of the process is higher than 97%. It is observed therefore that the use of an elevated temperature with the potential controlled process allows the use of much higher current densities than are observed in the prior art (causing more rapid copper deposition). Despite the high current densities used, a high level of purity is achieved together with a beneficial microstructure without dendrites.

Example 4

The experimental set-up and electrolysis conditions are the same as in Example 3 (including a process temperature of 60°C) although here the solution is stirred with a frequency of 50 rotations per minute. A shorter electrolysis period is used also.

Parameters of potentiostatic electrolysis:

Stainless steel cathode potential with reference to copper anode E= -0.450 V;

Electrolysis time t = 5 min

Stationary current density of approximately 1600 A m² at the cathode is achieved after constant potential -0.450 V has been applied to the electrodes for about 25 seconds.

After having deposited copper on the stainless steel cathode, the cathode deposit is removed from the cathode mechanically, washed with water, air-dried and the composition of the obtained copper is studied using an EDS/EDX method. It is found that the obtained cathode deposit has fine-crystalline structure without dendrites. Oxygen makes up about 0.05% of the weight and is the only/sole impurity present in the obtained cathode copper. So the obtained cathode copper has a purity higher than 99.95%. Having compared the deposited copper mass with the theoretical mass of copper that should have been deposited (calculated using Faraday's law), it is found that the current efficiency of the process is higher than 97%. Thus it is observed that the agitation of the electrolyte using stirring allows even higher current densities to be achieved under potential controlled conditions than in Example 3.

Note that in this case 5 minutes is a sufficient time scale to establish the "stationary" current density and to obtain enough copper to determine the copper mass with high precision.

Example 5 In this case the physical experimental arrangement is modified in comparison with the earlier examples to more closely represent an industrial refinery. Here there are 4 pairs (in fact, 4 cathodes and 5 anodes) of electrodes arranged in parallel and vertically placed in an electrochemical tank of volume of 120 litres made of polyvinylchloride. The cathodes are made of stainless steel sheet the thickness of which is 0.3 mm and cathode surface area is 0. 2 m², and the anode (reference electrode) is made of 0.25 mm thick copper sheet, the surface of which is 0.22 m². The distances between the cathodes and each of the anodes is 5 cm. The new potential control electrorefining method should be tested in different geometries since according to the theory macro-geometry of the electrolytic cell may influence considerably the limiting current established in natural convection conditions. The process is conducted at room temperature (about 20°C). The vessel is filled with an electrolyte of the same composition as presented in Example 1 although this is diluted 2.6 times with sulphuric acid of concentration of 180 g/dm³. Consequently, each of the electrolyte's component concentrations given in Example 1 , except of H₂S0₄, should be divided by 2.6 and so, for instance, the copper concentration is equal to 17.5 g/dm³. The electrodes are connected with the aid of a special cable to the commercially available rectifier which can be used to programme the duration of the potentiostatic electrolysis process from 1 minute to several days and which enables to conduct the studies at the current of up to 500 A flowing between the rectifier and the electrodes. The current changes depending on the duration of the electrolysis are measured during the process. The solution is not stirred in this example. Parameters of potentiostatic electrolysis:

Stainless steel cathode potential with reference to copper anode E= -0.350 V,

Electrolysis time t = 3 h

Stationary current density of approximately 100 A m² at the cathode is achieved after a constant potential -0.350 V has been applied to the electrodes for about 25 seconds.

After having deposited copper on the stainless steel cathode, the cathode deposit is removed from the cathode mechanically, washed with water, air-dried and the composition of the obtained copper is studied using EDS/EDX and ASTM copper elemental analysis methods. According to ASTM copper elemental analysis, the copper deposited copper has a purity >99.999%. The refined material has a smooth surface without nodules and dendrites.

It is found that the obtained cathode deposit has a fine-crystalline structure. Having compared the deposited copper mass as well as the theoretical mass of copper that should have been deposited using Faraday's law, it is found that the current efficiency of the process is higher than 96%.

This is a very important example since it demonstrates that copper electrorefining can be carried out effectively (with high purity, fine crystalline structure and high current efficiency) in conditions where the copper concentration is much lower than in traditional electrorefining, and where the temperature is much lower than in traditional, galvanostatic process. Example 6

The experimental set-up and electrolysis conditions are the same as in Example 5 except that one cathode and 2 anodes are used. The anodes are placed at an equal distance of 25 cm from each side of the cathode.

Parameters of potentiostatic electrolysis:

Stainless steel cathode potential with reference to copper anode E= -0.350 V,

Electrolysis time t = 2 h

Stationary current density of approximately 100 A m² at the cathode was achieved after a constant potential -0.350 V had been applied to the electrodes for about 25 seconds. After having deposited copper on the steel cathode, the cathode deposit is removed from the cathode mechanically, washed with water, air-dried and the composition of the obtained copper is studied using EDS/EDX and XRD methods. According to the EDS/EDX and XRD analysis the deposited copper has a purity >99.95%. It is found that the obtained cathode deposit has fine-crystalline structure. Having compared the deposited copper mass with the theoretical mass of copper that should have been deposited using Faraday's law, it is found that the current efficiency of the process is higher than 83%.

Example 7

The experimental set-up and electrolysis conditions are the same as in Example 6 except that, instead of a stainless steel cathode, a copper cathode made of 0.25 mm thick copper sheet is used, this having a surface of 0.22 m². Again, anodes are used. The anodes are placed, equally spaced from the cathode at distances of 5 cm on each side of the cathode. Additionally, the electrolyte composition is the same as in Example 1 except the copper content is equal to 41 g/dm³.

Parameters of potentiostatic electrolysis:

Copper sheet cathode potential with reference to copper anode E= -0.550V;

Electrolysis time t = 4 h;

with average current density of approximately 184 A m² at the cathode was achieved after a constant potential -0.550 V had been applied to the electrodes.

After having deposited copper on the copper cathode, the cathode deposit is removed from the cathode mechanically, washed with water, air-dried and the composition of the obtained copper is studied using EDS/EDX and XRD methods. According to the EDS/EDX and XRD analysis the deposited copper has a purity >99.95%. Again it is found that the deposited material has a smooth surface without nodules and dendrites. Having compared the deposited copper mass with the theoretical mass of copper that should have been deposited using Faraday's law, it is found that the current efficiency of the process is higher than 99%.

According to the website http://doccopper.tripod.com/copper/ertrend.html periodic current reversal (PCR) is being employed in at least 1 1 copper refineries (under current controlled conditions) to increase the rate of cathode production by increasing the applied current density. PCR is a method by which a forward current is applied for a length of time followed by a quick current reversal. The forward to reverse period ratio is typically between 20/1 to 30/1. According to the monograph by W.G. Davenport, M. King & M. Schlesinger, entitled Extractive Metallurgy of Copper p. 282 passivation of copper anodes at high cathodic current densities (when a galvanostatic controlled process is carried out) may also be avoided by periodically reversing the direction of the refining current. The advantage arises from the reversal current depleting the built up copper concentration within the anodic boundary layer. This helps avoid the precipitation of copper sulphate, which is one of the causes of passivation. The major disadvantage of PCR is higher energy costs. This has limited the use of this technology.

Unexpectedly the above-mentioned problems of current PCR have been solved by the present invention. The implementation of the present invention using either potential pulse electrolysis (PPE) or periodic potential reversal (PPR) enables the obtaining of copper deposits having a controlled surface area (roughness and/or porosity) and structure which may be applied in certain applications such as in organic chemical catalysis where copper tube flow reactors (CTFR) are used as reported e.g. in Org. Lett., 13 (2) (201 1 ) pp 280- 283. It has been stated in Sensors 7 (2007), 1 -15: "that the open and porous structures of copper deposits obtained at high current densities were ideally suited for use as electrodes in electrochemical devices such as fuel cells, batteries and chemical sensors, while the extremely high surface area is relevant for evaluating some electrochemical reactions. For example, it was known that copper shows a high activity for the nitrate ion reduction as well as for the reaction in which nitrate is reduced to ammonia in high yield in aqueous acidic perchlorate and sulphate media".

The method may therefore comprise a process of potentiostatic pulse electrolysis (PPE) or periodic potential reversal (PPR) copper deposition or a combination of PPR and PPE. Examples of potential pulse electrolysis (PPE) and periodic potential reversal (PPR) pulses applied to the cathode are presented in Figures 1 a to 1 d where: E_c is cathode potential, t_c is the length of cathodic pulse, E_a is the reverse pulse (anodic) potential applied to the cathode, t_a is the length of the potential reverse pulse (anodic) applied to the cathode. Advantageous implementations of PPE and PPR potentiostatic electrolysis processes are illustrated in Figure 3a) to 3d) in which:

Fig. 3a) shows a PPE process with cathodic potential pulses £_k in the range from -0.3V to -0.55V, in reference to the copper electrode, with a duration time f_k from 5 s to 18 000 s, and potential breaks between pulses (open circuit) with a duration time from 0.1 s to 100 s. The number of potential pulses and potential breaks is from 3 to 30.

Fig. 3b) shows a PPE process with different values of cathodic potential pulses E_c in the range from -0.3V to -0.55V, in reference to copper electrode, with a duration time t_c from 5 s to 18 000 s, and potential breaks (open circuit) between pulses from 0.1 s to 100s. The numbers of potential pulses and potential breaks is from 3 to 30.

Fig. 3c) shows a PPR process with the cathodic pulses in cathodic potential £_c in the range from -0.3 V to -0.55 V, in reference to copper electrode, with a duration time t_c from 5 s to 18 000 s, and then the anodic pulses in anodic potential E_ai in the range from +0.050 V to +0.6 V, in reference to copper electrode, with duration time f_ai at least 50% shorter than time t_c. The number of potential pulses and potential breaks is from 3 to 30.

Fig. 3d) shows a combination of PPE and PPR processes with the cathodic potential pulses E_c in the range from -0.3 V to -0.55 V, in reference to copper electrode, with duration time t_c from 5s to 18 000s, then the potential breaks between anodic and cathodic pulses (open circuit) with a duration time from 0.1 s to 100 s and anodic potential pulses Eao in the range from +0.050 V to +0.6 V, in reference to copper electrode, with duration time fao≤ t_c. The number of potential pulses and potential breaks is from 3 to 30.

Specific examples of the electrorefining of copper by PPE and PPR processes are now described in examples 8 to 10 below.

Example 8

In this example a pair of electrodes is provided in an electrochemical tank made of polyvinylchloride. The cathode is made of stainless steel sheet having a thickness of 0.3 mm. The anode (reference electrode) is made of 0.25 mm thick copper sheet the surface of which is 0.22 m². The process is conducted at room temperature (about 20°C). The vessel is filled with an electrolyte of the same composition as presented in Example 1. Each of the electrodes is connected with the aid of a special cable to a commercially available rectifier which can be used to programme the duration of a periodic potential reversal (PPR) electrolysis process. The duration of the applied potential may be controlled to be from 1 ms to several days, using a current of up to 500 A flowing between the rectifier and the electrodes. The current changes depending on the duration of the electrolysis are measured during the process. The solution is not stirred. Parameters of PPR electrolysis:

Cathodic pulse 1 :

E=-300mV

t= 5min

j= -360 A/m²

Cathodic pulse 2:

E=-350mV

t=5 min

j= -430 A/m²

Anodic pulse:

E=+400mV

t= 30s

l= +500 A/m²

The above sequence of pulses was repeated 3 times. After having deposited copper on the steel cathode, the cathode deposit is removed from the cathode mechanically, washed with water, air-dried and the composition of the obtained copper is studied using an EDS/EDX method and an X-ray diffraction (XRD) technique. It is found that the obtained cathode deposit has a fine crystalline structure without dendrites. During the anodic pulses the electrodeposited copper at the cathode undergoes anodic dissolution (corrosion) at the grain boundaries and consequently, the copper sheet surface roughness is much higher than in the case of potentiostatic electrolysis presented in Examples 1 to 7. Oxygen making up about 0.05% of the weight is the only/sole impurity present in the obtained cathode copper. So the obtained cathode copper has a purity higher than 99.95%. Having compared the deposited copper mass with the theoretical mass of copper that should have been deposited using Faraday's law, it is found that the current efficiency of the process is higher than 98%.

Example 9 The experimental set-up and electrolysis conditions are the same as in Example 8. Parameters of PPR electrolysis:

Cathodic pulse 1 :

E=-300mV

t= 5min

j= -490 A/m²

Cathodic pulse 2:

E=-350mV

t=5 min

j= -520 A/m²

Anodic pulse:

E=+600mV

t= 30s

l= +550 A/m²

The above sequence of pulses was repeated 3 times.

After having deposited copper on the steel cathode, the cathode deposit is removed from the cathode mechanically, washed with water, air-dried and the composition of the obtained copper is studied using an EDS/EDX method and an X-ray diffraction (XRD) technique. It is found that the obtained cathode deposit has coarse-crystalline structure without dendrites. During the anodic pulses the electrodeposited copper undergoes a pit corrosion and consequently the copper sheet surface roughness/porosity is much higher than in the case of potentiostatic electrolysis presented in Examples 1 to 7. Oxygen makes up about 0.05% of the weight and is the only/sole impurity present in the obtained cathode copper. So the obtained cathode copper has a purity higher than 99.95%.

Having compared the deposited copper mass as well as the theoretical mass of copper that should have been deposited using Faraday's law, it is found that the current efficiency of the process is higher than 97%.

Example 10

This example uses a PPE process, that is the application of cathodic pulses, interspersed with short zero potential breaks and without anodic pulses. The experimental set-up and electrolysis conditions are the same as in Example 8. Parameters of PPE electrolysis:

Cathodic pulse 1 :

E=-300mV

t= 5min

j= -460 A/m²

Potential break:

E= OmV

t= 1 s

l= 0 A/m²

Cathodic pulse 2:

E=-450mV

t=5 min

j= -560 A/m²

The above sequence of pulses was repeated 3 times.

After having deposited copper on the steel cathode, the cathode deposit is removed from the cathode mechanically, washed with water, air-dried and the composition of the obtained copper is studied using an EDS/EDX method and an X-ray diffraction (XRD) technique. It is found that the obtained cathode deposit has a columnar-crystalline structure without dendrites and consequently the copper sheet surface roughness is higher than in the case of potentiostatic electrolysis presented in Examples 1 to 7. Oxygen makes up about 0.05% of the weight and is the only/sole impurity present in the obtained cathode copper. So the obtained cathode copper has a purity higher than 99.95%. Having compared the deposited copper with the theoretical mass of copper that should have been deposited using Faraday's law, it is found that the current efficiency of the process is higher than 98%.

Industrial Implementation It will be understood that each of the above examples demonstrates the industrial application of the invention. Of course in implementing the invention on an industrial scale optimisation of the processes should be performed by tailoring the parameters regarding the process to the particular industrial process in question. This may involve optimising such parameters as the size, geometry, and relative positions of the anodes and cathodes, the controlling of the electrolyte processing, including content and flow, the process temperature and of course the optimisation of the electrical potential control conditions. In this way, using the guidance provided by the above examples, the most efficient process for a desired combination of copper deposition rate and quality may be achieved.

Claims

A method of industrial copper electrorefining comprising, arranging at least one anode of copper material to be refined in contact with an electrolyte solution; arranging at least one cathode in contact with the electrolyte solution; electrically connecting the anode and cathode to an electrical source, and operating the electrical source under electrical potential controlled conditions such that during at least part of the application of the said conditions, the electrical potential at the cathode is -0.30 V to -0.55 V with respect to the copper material at the anode, thereby causing the deposition of electrorefined copper at the cathode.

A method according to claim 1 , wherein the electrical potential controlled conditions include the application of complex form potential.

A method according to claim 2, wherein, during the said conditions, one or more of the magnitude and polarity of the electrical potential are modulated.

A method according to claim 3, wherein the electrical potential is modulated as a rectangular waveform having a magnitude of the electrical potential at the cathode of between -0.30 V and -0.55 V.

A method according to any of claims 1 to 3, wherein the said conditions include potentiostatic pulse electrolysis (PPE) conditions in which a number of cathodic pulses in the range 3 to 300 are applied, each having a substantially constant potential in the range -0.30V to -0.55V with reference to the copper material at the anode, and each having a duration of between 5 and 18000 seconds, wherein the pulses are separated in time by open circuit breaks, each having a duration in the range 0.1 to 100 seconds.

A method according to any of claims 1 to 3, wherein the said conditions include periodic potential reversal (PPR) conditions in which a cathodic pulse having a potential in the range -0.30 V to -0.55 V, with reference to copper material anode is applied for a duration in the range 5 to 18 000 seconds, the cathodic pulse being followed by an anodic pulse in the range of +0.05 V to +0.60 V, with reference to the copper material anode, whereby the duration of the anodic pulse is shorter than the cathodic pulse by at least 50% and wherein the sequence formed from the cathodic pulse and anodic pulse is repeated from 3 to 30 times.

A method according to any of claims 1 to 3, wherein the said conditions include periodic potential reversal (PPR) conditions in which a cathodic pulse having a potential in the range -0.30 V to -0.55 V, with reference to copper material anode is applied for a duration in the range 5 to 18 000 seconds, the cathodic pulse being followed by an anodic pulse in the range of +0.05 V to +0.60 V, with reference to the copper material anode, whereby the duration of the anodic pulse is shorter than the cathodic pulse and wherein open circuit conditions are applied for a period between the cathodic and anodic pulses and the sequence formed from the cathodic pulse and anodic pulse is repeated from 3 to 30 times.

8. A method according to claim 7, wherein the said open circuit conditions are applied twice during the sequence as the potential is reversed.

9. A method according to any of the preceding claims, wherein the said at least one anode and at least one cathode are arranged as at least one pair and wherein the distance between the cathode and anode in a pair is 5 cm or less.

10. A method according to any of the preceding claims, wherein the current efficiency of the process is 95% or more.

1 1 . A method according to any of the preceding claims, wherein an electrolyte comprising 90 g/dm³ to 200 g/dm³ H₂S0₄ and 1 g/dm³ to 50g/dm³ Cu is used.

12. A method according to any of the preceding claims, wherein the method is carried out at the temperature of 18°C to 65°C.

13. A method according to claim 12, wherein the method is carried out at a temperature of 18°C to 30°C.

14. A method according to any of the preceding claims, further comprising, initially forming the said at least one anode from a fire-refined, scrap or recycled copper material.

15. A method according to any of the preceding claims, wherein the method is performed using a cathode made of stainless steel or copper.

16. A method according to any of the preceding claims, further comprising causing the electrolyte to be in motion with respect to the anode and cathode during the electrorefining.

17. A method according to any of the preceding claims, wherein the electrolyte is substantially free of any organic additive.

18. A method according to any of the preceding claims, wherein the refined copper has a purity in excess of 99.95%.

19. An industrial copper electrorefining system comprising:

a container for retaining an industrial electrolyte;

at least one first electrode formed from copper material to be refined and being positioned within use in contact with the industrial electrolyte within the container; at least one second electrode positioned within use in contact with the industrial electrolyte within the container; and, a power supply operable under electrical potential controlled conditions and connected electrically when in use to each of the said at least one first and at least one second electrodes, such that during at least part of the application of the said conditions, the electrical potential at the at least one second electrode is -0.30 V to -0.55 V with respect to the copper material at the at least one first electrode, thereby causing the deposition of electrorefined copper at the at least one second electrode.

20. A system according to claim 19, further comprising an electrolyte management system arranged to control the movement of the electrolyte within the tank and to modulate the composition of the electrolyte during the electrorefining process.

21 . Apparatus according to claim 19 or claim 20, further adapted in use to perform the method according to any of claims 1 to 18.