RU2780328C1 - Advanced production of tin including a composition containing tin, lead, silver, and antimony - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the extraction of silver in production of tin, namely to the separation of silver through fractional crystallisation. Method includes separating, by fractional crystallisation (300), a molten mixture (8) of crude tin containing lead and silver into a first liquid silver-enriched discharged product (9) on the side of the liquid fraction produced at the crystallisation stage, and a first tin-enriched product (10) on the side of the crystalline fraction produced at the crystallisation stage. The metal composition produced in the form of the first liquid silver-enriched discharge product (9) herein consists, as calculated by dry weight, of 6.0 to 27.5% wt. lead, 72.5 to 91% wt. tin, 95.0 to 99.0% wt. combined lead and tin, 0.75 to 4.50% wt. silver, and at least 0.24% wt. antimony.

EFFECT: concentration of silver in the discharged product is increased.

37 cl, 1 dwg, 10 tbl, 1 ex

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

The present invention relates to the recovery of silver in the production of tin (Sn), possibly in combination with the production of copper (Cu) and lead (Pb), from primary and/or recycled sources. More specifically, the present invention relates to the separation of silver from the molten black tin mixture by fractional crystallization.

BACKGROUND OF THE INVENTION

Silver is undesirable as a contaminant of tin metal. The significant presence of silver in metallic tin causes a deterioration in the mechanical properties of metallic tin. In addition, the presence of silver in tin, which is used in tinning steel, creates the risk of electrochemical corrosion, which will corrode the tin wall from the inside to the outside. This is an important issue for cans to be used in the food industry.

Other end uses of tin can also be sensitive to contaminants and similarly require high purity tin quality. This applies, for example, to the production of lead-free high-grade solder in the production of semiconductor compounds such as tin nitride, antimony telluride, tin arsenide, and semiconductor alloys.

Silver is also a metal with a significant market value, usually much higher than the market value of the most common non-ferrous metals such as copper and lead, and even than the market value of tin. Silver can be found in small quantities in commercially available raw materials of other non-ferrous metals such as copper, lead and/or tin, and in particular in secondary raw materials for the production of these metals. However, silver concentrations in non-ferrous metal-containing streams from pyrometallurgical refining steps in the production of copper and/or lead are very low, usually too low to warrant separate recovery. The authors found that when tin is present in the pyrometallurgical refining of copper and/or lead and the recovery of streams with increased concentration of tin is part of the same process, metallic silver may tend to repeat the main path of metallic tin through this process and end up in process streams, containing tin, including solder flows based on a mixture of Pb and Sn. However, the silver concentrations in these pyrometallurgical streams containing tin are still relatively low. However, when the process involves the recovery of a high purity tin metal base product, silver levels easily become so high as to be undesirable in the tin base product.

Therefore, there has been a need to recover silver from streams containing tin and having relatively low levels of silver, such as lead/tin mixtures, often referred to as "solder" streams.

CN205710871(U) and CN105970003(A) disclose a method for recovering silver from raw solder containing Sn/Pb/Ag (62-78%, 20-38%, 0.2-2.0% by weight). The molten solder is contacted with molten zinc to form two intermetallic compounds having high melting points: Ag ₂ Zn ₃ (665°C) and/or Ag ₂ Zn ₅ (636°C). These hard intermetallic compounds can be easily separated as a silver-zinc alloy from molten solder having a melting point of 185-190°C in a mold type apparatus by creating a temperature profile in the range from 410-430°C to 220-200 °C with step reduction in six or eight temperature zones of the device. The disadvantage of this method is that silver is obtained in a chemically bound form as part of intermetallic compounds, which makes its extraction more difficult.

It is also known to use fractional crystallization in the treatment of tin-containing molten metal streams.

CN 103667744 discloses a batch two-stage fractional crystallization process for upgrading 99.9+% purity tin to 99.99+% purity tin. In the first step, at the high temperature end of the mold, a tin alloy containing at most 99.88 wt% tin and having an increased concentration of arsenic, copper, iron and antimony is separated from the eutectic alloy contained in the 6-zone mold. In the second step, using a different temperature profile in the same equipment at the lower temperature end of the mold, a eutectic alloy containing at most 99.91 wt.% tin and having an increased concentration of lead, indium and bismuth is separated from the product in in the form of tin with a specified degree of purity of 99.99+%. Only about half of the starting material in the form of tin with a purity of 99.9+%, in the end, the main product is obtained in the form of tin with a purity of 99.99+%. Therefore, the disadvantages of this technological process are a large number of by-products in the form of lower grade tin alloys, the complexity of the technological process and the need to perform this technological process in batch mode. The by-products still have a very low concentration of any element other than tin and are therefore not a source of interest for their recovery. The silver concentration in this process is extremely low, ie 5 ppm at the most. by weight in starting materials and at most 21 ppm. by weight in the by-product obtained in step 2. Obviously, the document CN 103667744 does not refer to the recovery of small amounts of silver in the starting materials.

CN 102534249 B describes a process in which fractional crystallization separates out a significant amount of tin present in a crude tin feedstock with a high silver concentration, additionally containing about 8% lead and about 1% by weight silver. The purpose of the process is to reduce the volume of the mixture of metals before feeding this mixture to the operation of the electrolytic separation of precious metals, and it is stated that in this process there is a decrease in volume in the range of 10-30% of the initial volume before the crystallization step. The mold is filled with black tin and the temperatures in 4 zones or 4 stages are controlled within predetermined intervals, with temperatures rising from zone 1 (approximately 235°C) to zone 4 (approximately 650°C). Black tin is continuously fed into the mold and solder by-product is continuously withdrawn. The resulting refined tin accumulates in the form of crystals at the hot end of the mold and contains at least 99.96 wt.% tin, less than 0.03 wt.% lead and less than 100 ppm. silver by weight. The solder, which is obtained by means of a mold, contains 20-30 wt.% lead and 2.5-4.6 wt.% silver, while the rest is tin, and it is provided that this solder is sent to the subsequent electrolysis stage for the electrolytic separation of noble metals. This method reduces the amount of material that needs to be processed through the subsequent electrolysis step to only 10-30% compared to the same method without an intermediate crystallization step. The disadvantage of the method according to CN 102534249 B is that it achieves a concentration factor of only at most 4, which characterizes the change in silver concentration from the starting material to the by-product withdrawn. The process may be suitable for processing feedstocks in which the level of silver content is already significant (approximately 1 wt %). In the case of raw materials with a lower concentration of silver, this method leaves much to be desired. Another disadvantage is that the amount of product withdrawn obtained is still large and is even about 1/4-1/3 of the amount of starting material that is fed into the mold.

Therefore, there remains a need for a process for recovering silver from tin-containing molten metal streams that allows operation initially with a feedstock having a fairly low tin content, but which at the same time allows silver to be produced in a by-product stream having a sufficiently high silver content, so that this stream is considered as a raw material suitable for the extraction of silver from it.

The present invention is directed to eliminating or at least reducing the severity of the above described problem and/or to provide improvements in general.

SUMMARY OF THE INVENTION

The invention provides a metal composition and method as defined in the appended claims.

In an embodiment of the present invention, a metal composition is provided comprising, on a dry weight basis:

- at least 6.0 wt.% and at most 30.0 wt.% lead;

- at least 70.0 wt.% and at most 91 wt.% tin;

- at least 95.0 wt.% and at most 99.0 wt.% lead and tin together;

- at least 0.75 wt.% and at most 5.00 wt.% silver; and

- at least 0.24 wt.% antimony.

In another embodiment, the present invention provides a metal composition consisting, on a dry weight basis, of:

- at least 6.0 wt.% and at most 30.0 wt.% lead;

- at least 70.0 wt.% and at most 91 wt.% tin;

- at least 95.0 wt.% and at most 99.0 wt.% lead and tin together;

- at least 0.75 wt.% and at most 5.00 wt.% silver; and

- at least 0.24 wt.% antimony,

and optionally additionally containing, also on a dry weight basis:

- at least 0.05 wt.% and at most 0.5 wt.% arsenic;

- at least 0.05 wt.% and at most 0.6 wt.% copper;

- at least 0.0030 wt.% and at most 0.0500 wt.% nickel;

- at least 0.0010 wt.% and at most 0.40 wt.% bismuth;

- at most 1.0 wt.% iron and

- at least 0.0005 wt.% and preferably at most 0.0500% gold,

while the rest are impurities.

The inventors have found that the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the crystallizer in the method according to the present invention, further described below, is, surprisingly, a suitable raw material for recovering silver through the step electrolysis, in which the cathode collects most of the Sn and Pb and optionally also some of the Sb from the anode cast from the given metal composition, and the silver accumulates as part of the anode sludge. A suitable technical solution for this electrolytic refining step is to use an electrolyte based on hexafluorosilicic acid (H ₂ SiF ₆ ), fluoroboric acid and/or phenylsulfonic acid, temperature of approximately 35-40°C, current density in the range of 100-200 A /m ² , and the distance between the electrodes, which is approximately 100 mm.

The inventors have found that during the electrolysis of anodes cast from the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, the resulting anode sludge remains more adherent to the anode and significantly less anode sludge can be dispersed in the electrolyte, if at all. This is a significant advantage in the recovery of the anode sludge generated during this electrolysis step. The anode after a period of use may be removed from the electrolysis cell and the anode sludge may be scraped off the anode. The cleaned anode may then be returned to the cell for further use, or may be returned for processing as "spent anode" to a previous anode casting step.

This anode sludge recovery method is much simpler than the traditional method, in which the anode sludge is dispersed in the electrolyte, can accumulate at the bottom of the cell, and must be recovered as a filter cake obtained from the settling and/or filtration step included in the electrolyte treatment cycle. , or in the pump used in the area of the cell. The conventional method also involves the use of flocculants and other chemicals that are designed to aid and improve the settling and/or filtration steps and which may affect the electrolysis step itself and/or end up in the anode sludge product.

Without wishing to be bound by this theory, the authors believe that the advantage of the metal composition according to the present invention - which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention - is that the anode sludge, formed during electrolysis, remains adhered to the anode, provided by the minimum specified presence of antimony in the metal composition, if necessary "enhanced" by bismuth, which is believed to contribute the same effect. The authors believe that this effect can be easily achieved when the level of antimony concentration in the metal composition according to the present invention is not excessively high, that is, less than 5 wt.%, while compliance with this condition is essentially ensured due to the lower limits of the content of tin and lead together, as well as silver.

The inventors have found that the presence of tin and lead, in their relative proportions, also provides an advantage to the metal composition of the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the process of the present invention. On the state diagram of the two-phase system Pb - Sn, this composition is on the side of tin in relation to the eutectic composition, where the melting points are lower than on the side of lead on the phase diagram of the two-component system. This provides the advantage that the melting point and/or viscosity of the metal composition according to the present invention is lower. This provides advantages in casting anodes from the metal composition according to the present invention, since the lower viscosity provides the advantage of better mold filling and the lower melting temperature provides the advantage of greater dimensional stability of the cast anodes, resulting in, for example, less risk warping or other types of deformation during the cooling of the anode after it has been cast.

In addition, the authors found that a large amount of tin in relation to antimony, essentially given the conditions specified for the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contributes to the stable performance of the described electrolysis step, since the content of ions in the electrolyte remains more constant for a long time.

In an embodiment of the present invention, a process is provided for fractional crystallization of a molten mixture with black tin containing lead and silver to obtain a first liquid withdrawal product with an increased concentration of silver on the side of the liquid fraction obtained from the crystallization stage, and a first product with an increased concentration of tin on the side of the crystal the fraction obtained at the stage of crystallization, while the first liquid discharged product with a high concentration of silver contains, in terms of weight in a dry state:

- at least 6.0 wt.% and at most 30.0 wt.% lead;

- at least 70.0 wt.% and at most 91 wt.% tin;

- at least 95.0 wt.% and at most 99.0 wt.% lead and tin together;

- at least 0.75 wt.% and at most 5.00 wt.% silver; and

- at least 0.24 wt.% antimony.

In another embodiment of the process according to the present invention, the first liquid product with increased silver concentration consists, on a dry weight basis, of:

- at least 6.0 wt.% and at most 30.0 wt.% lead;

- at least 70.0 wt.% and at most 91 wt.% tin;

- at least 95.0 wt.% and at most 99.0 wt.% lead and tin together;

- at least 0.75 wt.% and at most 5.00 wt.% silver; and

- at least 0.24 wt.% antimony,

and optionally additionally also contains, on a dry weight basis:

- at least 0.05 wt.% and at most 0.5 wt.% arsenic;

- at least 0.05 wt.% and at most 0.6 wt.% copper;

- at least 0.0030 wt.% and at most 0.0500 wt.% nickel;

- at least 0.0010 wt.% and at most 0.40 wt.% bismuth;

- at most 1.0 wt.% iron and

- at least 0.0005 wt.% and preferably at most 0.0500% gold,

while the rest are impurities.

In an embodiment of the method according to the present invention, a metal composition according to the present invention is prepared, and the method according to the present invention is characterized in that the black tin mixture contains at least 0.1 wt.% and at most 7.0 wt.% lead.

In an embodiment of the present invention, a method is provided for fractional crystallization of a molten black tin mixture containing silver to obtain a first liquid effluent product with an increased concentration of silver on the side of the liquid fraction obtained in the crystallization step, and a first product with an increased concentration of tin on the side of the crystalline fraction, obtained at the stage of crystallization, characterized in that the mixture with black tin contains at least 0.1 wt.% and at most 7.0 wt.% lead.

The authors have found that the presence of lead in this range provides significant advantages for the method according to the present invention and for at least some of the products obtained through this method.

One advantage is that the minimum presence of lead in the specified amount in the starting material for the fractional crystallization step is a factor contributing to the performance of the process in the fractional crystallization step.

A mixture of 38.1 wt.% Pb and 61.9 wt.% Sn has a melting point of only 183°C, which is lower than the melting points of pure lead (327.5°C) and pure tin (232°C). A mixture of Pb / Sn in a percentage ratio of 38.1 / 61.9 is called the eutectic composition. When a molten tin/lead binary mixture having a composition that differs from the eutectic composition is cooled, crystals are formed that have a composition that differs even more from the eutectic composition, and a liquid phase remains that has a composition closer to the eutectic composition. The authors found that this phenomenon allows the separation of a mixture of lead and tin through fractional crystallization into a product that has an increased concentration of either Sn or Pb on the side of the crystalline fraction and a product that has a composition closer to the eutectic composition on the side of the liquid fraction . Thus, the minimum presence of lead in the starting material allows the separation - by fractional crystallization - of a product in the form of tin of higher purity on the side of the crystalline fraction from a liquid product having a higher concentration of lead than the starting material.

In addition, the authors found that in the case of a mixture of lead and tin, which contains more tin than the eutectic mixture of tin and lead, and in the case that this mixture additionally contains relatively small amounts of silver, when the fractional crystallization of the mixture silver tends to remain together with most of the lead is in the liquid phase and tin crystals can be obtained which have a much lower content of silver and lead. The authors found that lead serves as a carrier for silver. In addition, the authors found that in such a fractional crystallization process, the concentration of silver can rise from a lower level in the original feed mixture to a higher level in the liquid product obtained in the crystallizer.

In addition, the inventors have found that in the case where the amount of lead in the raw material fed to the fractional crystallization step is kept below the specified upper limit, the increase in the concentration of silver from the raw material to the liquid product obtained in the crystallizer can be significantly increased. The inventors have found that this makes it possible to process feedstocks that have relatively low silver concentrations and still obtain a product stream that has a limited volume and a greatly increased silver content, so that it becomes suitable for further processing to recover silver.

In addition, the authors found that in the case where the content of lead in the first liquid effluent product with an increased concentration of silver is maintained in accordance with the specified upper limit and the content of tin in the same product stream is maintained in accordance with the specified lower limit, in the part of the method that corresponds to fractional crystallization, a smaller number of steps/stages are needed to ensure a given separation and increase the concentration of silver in the withdrawn product compared to the starting material.

BRIEF DESCRIPTION OF THE DRAWINGS

1 shows a flow chart of a larger overall process including a preferred embodiment of the method/process of the present invention.

DETAILED DESCRIPTION

In the following, the present invention will be described in connection with specific embodiments and with possible reference to specific drawings, but the invention is not limited by them, but only by the claims. Any drawings described are only schematic and non-limiting. In the drawings, the size of some of the elements may be exaggerated and some elements may not be drawn to scale for purposes of illustration. The dimensions and dimensions in the drawings do not necessarily correspond to the actual practice of the invention.

In addition, the terms "first", "second", "third" and the like in the specification and 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 be carried out in sequences other than those described and/or illustrated herein.

In addition, the terms "upper", "lower", "above", "under" and the like in the description and in the claims are used for the purpose of description and optionally for describing relative positions. The terms used in this manner are interchangeable under appropriate circumstances, and the embodiments of the invention described herein may be practiced in orientations other than those described and/or illustrated herein.

The term "comprising" used in the claims should not be construed as limited to the elements that are listed in connection with it. It does not exclude the presence of other elements or steps. It should be considered as indicating the presence of these elements, integer objects, steps or components as required, but it does not preclude the presence or addition of one or more other elements, integer objects, steps or components, or groups thereof. Thus, the scope of the expression "product containing means A and B" may not be limited to an object that consists only of means A and B. This expression means that A and B are the only elements of interest to the subject of the present invention. Accordingly, the terms "comprise" or "include" also encompass the more restrictive terms "consisting essentially of" or "consisting of". Therefore, when the terms "comprise" or "include" are replaced by the term "consist of", these terms form the basis for preferred but narrowed embodiments, which are also given as part of the content of this document related to the present invention.

Unless otherwise indicated, all ranges given herein include values up to and including the end points given, and the values of constituents or components of the compositions are expressed as weight percent or wt.% of each ingredient in the composition.

In the context of this document, the terms “wt%”, “wt%” (“%wt”), “wt%” (“wt-%”), “percent by weight”, “wt%” (“% by weight”), “parts per million (ppm) by mass” (“ppm wt”), “ppm wt. by mass” (“ppmwt”), “ppm by weight” (“ppm by weight”), “ppm by weight” (“weight ppm”) or “ppm” (“ppm”) and variations thereof refer to the concentration of a substance as the mass of that substance divided by the total mass of the composition and multiplied by 100 or 1,000,000, as appropriate, unless otherwise noted. It should be understood that in the context of this document it is provided that the term "percentage" and the designation "%" are synonymous with "mass percent", "wt.%", etc.

It should be noted that, as used in this specification and the appended claims, the singular forms with articles cover the referenced objects in the plural, unless the content explicitly specifies otherwise. Thus, for example, reference to a composition containing a "compound" encompasses a composition having two or more compounds. It should also be noted that the term "or" is generally used in its sense of "and/or" unless the content explicitly specifies otherwise.

In addition, each compound used herein may be referred to by its chemical formula, chemical name, abbreviation, and so on. in an interchangeable way.

Most of the metal streams in the process according to the present invention contain most of the lead, often in combination with a significant amount of tin. Such streams have a relatively low melting point and have been used for centuries to attach one solid to another solid through a process often referred to as "soldering". Therefore, such streams are often referred to as so-called "solder" or "solder" streams, and the term is also used herein to refer to such streams.

Of the metals to be recovered in accordance with the present invention, Sn and Pb are considered "braze/soft solder metals". These metals differ from other metals, in particular copper and nickel, because mixtures containing large amounts of these metals usually have a significantly lower melting point than mixtures containing large amounts of copper and/or nickel. Similar compositions have already been used thousands of years ago to create a permanent connection between two pieces of metal, and this is done by first melting the "solder", placing it in a given place and allowing it to solidify. Therefore, the solder had to have a lower melting point than the metal of the pieces it joined. In the context of the present invention, a solder product or solder metal composition, two terms used interchangeably throughout this document, means metal compositions in which the combination of solder metals, hence the Pb content combined with Sn, forms the majority of the composition. , i.e. at least 50 wt.% and preferably at least 65 wt.% The solder product may additionally have minor levels of other metals to be recovered, namely copper and/or nickel, and metals not specified for extracts such as Sb, As, Bi, Zn, Al and/or Fe and/or elements such as Si.

In this document, and unless otherwise indicated, the amounts of metals and oxides are expressed in accordance with standard practice in pyrometallurgy. The presence of each metal is generally expressed as its total presence, whether the metal is present in its elemental form (oxidation state=0) or in any chemically bonded form, typically as an oxide (oxidation state > 0). In the case of metals that can be relatively easily reduced to their elemental species, and which may be in the form of molten metal in a pyrometallurgical process, it is quite common to express their presence in terms of their elemental metal form, even when the composition of the slag or dross is given, and most of these metals may actually be present as oxides and/or in chemically bonded form. From this it follows that in the composition of the mixture of metals as the source material supplied to stage (a), the content of Fe, Zn, Pb, Cu, Sb, Bi is indicated as the content of elemental metals. Less noble metals are more difficult to reduce under the conditions of pyrometallurgical processes for the production of non-ferrous metals and are found mostly in the form of oxides. These metals are generally listed as their most commonly occurring oxides. Therefore, when specifying the compositions of slag or dross, the content of Si, Ca, Al, Na, as a rule, is given in the form of the corresponding content of SiO ₂ , CaO, Al ₂ O ₃ , Na ₂ O.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at least 6.5 wt.% lead, preferably at least 7.0 wt.%, more preferably at least 8.0 wt.%, even more preferably at least 9.0 wt.%, preferably at least 10.0 wt.%, more preferably at least 11.0 wt. %, even more preferably at least 12.0 wt.%, preferably at least 13.0 wt.%, more preferably at least 14.0 wt.%, even more preferably at least 15.0 wt.% lead. Lead is a contributing element to the prior process in which the metal composition of the present invention is made, since the ability to recover silver from crude tin by fractional crystallization relies on the presence of a lower melting point eutectic mixture in a two-component system of lead and tin in the phase diagram. .

The authors prefer to have a lead content in the metal composition according to the present invention that exceeds the specified lower limit, since the higher lead content in the outlet product obtained from the fractional crystallization step, which produces the metal composition according to the present invention, in relation to the lead content in the starting material, fed to the fractional crystallization stage provides a higher silver concentration factor, determined from the ratio of the silver concentration in the effluent obtained from the crystallization stage to the silver concentration in the feedstock fed to the fractional crystallization stage. A higher concentration factor has the advantage of being able to process a feedstock that has a lower silver concentration with the same effluent and/or a higher silver concentration effluent for a feedstock with the same silver content.

The higher amount of lead in the metal composition of the present invention also makes the composition more suitable for on-line recovery of lead, tin and antimony by electrolysis combined with pyrometallurgy. More lead also means more lead in the cathodes produced in the electrolysis step discussed above. When these cathodes are subjected to a vacuum distillation step to separate lead and antimony from tin and to obtain a high-purity tin precursor product from which high-purity tin main product can be readily obtained by chemical refining, lead serves as a carrier for antimony. Lead aids in separating antimony from tin and therefore a higher level of lead is desirable in the metal composition of the present invention.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at most 27.5 wt.%, preferably at most 25.0 wt.% , more preferably at most 22.5 wt.%, preferably at most 20.0 wt.%, more preferably at most 17.5 wt.%, even more preferably at most 15.0 wt.% lead. The level of lead in combination with the level of tin is preferably such that the metal composition, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the process according to the present invention, is on the proper side with respect to the eutectic composition in the phase diagram. of the Pb/Sn two-component system, so that the tin is concentrated as a crystalline product coming out of the hot end crystallization step and most of the lead is at the end in the bypass product which comes out of the cold end crystallization step and whose composition is closer to the eutectic composition according to compared with the composition of the original material. The authors found that compliance with the specified upper limit of lead content also reduces the risk of crystal build-up on the screw blades inside the mold, since the flow composition remains more different from the eutectic composition.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at least 72.5 wt.%, preferably at least 75.0 wt. .%, more preferably at least 77.5 wt.%, even more preferably at least 80.0 wt.%, preferably at least 81.0 wt.%, more preferably at least 82.0 wt.% , even more preferably at least 83.0 wt.%, preferably at least 84.0 wt.%, more preferably at least 85.0 wt.%, even more preferably at least 87.5 wt.% tin . Tin is also a contributing element to the prior process in which the metal composition of the present invention is produced, which is preferably obtained as the first liquid product with a higher concentration of silver withdrawn from the mold in the process of the present invention, since the possibility of recovering silver from crude tin through fractional crystallization is based on the presence of a lower melting eutectic composition in a two-component system of lead and tin in the phase diagram. The level of tin in combination with the level of lead is preferably such that the metal composition, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, is on the proper side with respect to the eutectic composition in the phase diagram of the Pb/Sn two-component system, so that the tin is concentrated as a crystalline product coming out of the hot end crystallization step and most of the lead is at the end in the bypass product which comes out of the cold end crystallization step and whose composition is closer to the eutectic composition according to compared with the composition of the original material. The inventors have found that this set of parameters ensures that the silver from the raw material fed to the crystallizer is concentrated in the effluent, and therefore recovers the silver by separating the silver from the tin-rich product produced by the crystallizer.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at most 90 wt.% tin, preferably at most 89.0 wt.%, more preferably at most 88 wt%, even more preferably at most 87 wt%, preferably at most 86 wt%, more preferably at most 85 wt%, even more preferably at most 84.5 wt%, preferably at most more than 84.0 wt.%, more preferably at most 83.0 wt.%, even more preferably at most 82.0 wt.% tin. The authors have found that meeting the upper limit of tin provides the advantage that there is the possibility of having more lead in the composition. Since more lead provides the advantage of being able to have a higher silver concentration factor in the upstream mold step, a lower tin content provides the advantage of having the highest possible silver content in the metal composition of the present invention, which is preferably obtained as of the first liquid high silver product withdrawn from the crystallizer in the process of the present invention, in combination with the lower level of silver in the high tin product obtained on the crystalline fraction side of the previous crystallization step, all of which together means, that more available silver will end up in a given product that can be upgraded to a silver product suitable for industrial use. This provides the advantage that more high-value silver can be recovered for the same amount of metal composition, or that for the same amount of silver to be recovered from the metal composition of the present invention, which is preferably obtained as a first liquid product with an increased concentration of silver removed from the mold in the process of the present invention will require less metal composition to be processed, and less Sn/Pb by-product will need to be processed after subsequent separation of most of the tin and lead from silver.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at least 95.25 wt.% lead and tin together, preferably at least 95.5 wt%, more preferably at least 95.75 wt%, even more preferably at least 96.00 wt%, preferably at least 96.25 wt%, preferably at least 96.5 wt.%, more preferably at least 96.75 wt.%, even more preferably at least 97.00 wt.% tin and lead together. The higher content of Sn+Pb provides the advantage that the metal composition according to the present invention may contain fewer undesirable elements. The inventors have found that in addition to lead and tin and silver as the metal to be recovered, some antimony and a limited amount of arsenic may also be acceptable, but the concentration of a number of other elements is preferably kept at trace levels. One such element is, for example, iron (Fe), since this element can create problems during the electrolysis step, which can recover anode sludge with a high concentration of silver, and at the same time can ensure the precipitation of most of the tin and lead in the by-product. on the cathode. The mechanism by which iron can influence electrolysis is described in detail in WO 2019/219821 A1. Other elements, such as nickel, may also result in additional electrolysis costs, and higher levels of copper may necessitate additional steps in post-treatment of the metal composition of the present invention and/or products derived therefrom. For example, the inventors prefer that the level of copper remained limited in the metal composition of the present invention, which is preferably produced as the first liquid product with an increased concentration of silver withdrawn from the crystallizer in the process of the present invention, since it is believed that copper interferes with the manifestation of the preferential effect, provided by the presence of antimony and/or bismuth. Thus, the higher lead and tin levels together contribute to all of these benefits.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at most 98.75 wt.% lead and tin together, preferably at most 98, 50 wt%, more preferably at most 98.25 wt%, even more preferably at most 98.00 wt%, preferably at most 97.75 wt%, more preferably at most 97.50 wt%, still more preferably at most 97.25 wt%, preferably at most 97.00 wt%, more preferably at most 96.75 wt%, even more preferably at most 96.50 wt% of lead and tin together. Keeping the lead and tin content together below the specified upper limit provides the advantage that it is possible for a given metallic silver to be present in greater amounts in the composition, i.e. considering its economic value, and the presence of elements such as antimony and bismuth, which are desirable. due to the positive effects they provide, as described above. The metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the crystallizer in the method according to the present invention, preferably does not contain any other metals other than lead, tin, silver, bismuth and antimony, in concentrations exceeding trace levels. For copper, a concentration of 0.5 wt.% also corresponds to a metal trace and is usually an unintended consequence of the fact that the metal composition according to the present invention is a by-product in the refining of copper. As for the remaining metals, the concentration level corresponding to the trace amount is preferably at most 0.2 wt.% for each of them. More preferably, the concentration levels of elements other than lead, tin, silver, bismuth, antimony, copper, arsenic and indium are at most 0.05% by weight for each.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at least 0.90 wt.% silver, preferably at least 1.00 wt.%, more preferably at least 1.25 wt.%, even more preferably at least 1.50 wt.%, preferably at least 1.60 wt.%, preferably at least 1.70 wt.% , more preferably at least 1.75 wt.%, even more preferably at least 2.00 wt.% silver. Silver is the target/target metal in the first silver concentrated liquid product that is withdrawn from the crystallizer, which may also be the metal composition of the present invention. Silver is an element that has a higher market value than other metals discussed in this regard in this document. A higher level of silver provides the advantage that the metal composition is of greater economic interest.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at most 4.50 wt.% silver, preferably at most 4.00 wt. %, more preferably at most 3.50 wt.%, even more preferably at most 3.00 wt.%, preferably at most 2.75 wt.%, more preferably at most 2.50 wt.%, even more preferably at most more than 2.25 wt.%, preferably at most 2.00 wt.%, more preferably at most 1.75 wt.%, even more preferably at most 1.50 wt.% silver. The inventors prefer to comply with this upper silver content limit as this creates the possibility of complying with the lower content limit given above for silver and tin together, and therefore opens up the possibility of providing the effects associated with them.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at least 0.25 wt.% antimony, preferably at least 0.30 wt.%, more preferably at least 0.35 wt.%, even more preferably at least 0.40 wt.%, preferably at least 0.45 wt.%, preferably at least 0.50 wt.% , more preferably at least 0.55 wt.%, even more preferably at least 0.60 wt.% antimony. The benefits provided by antimony in the metal composition of the present invention are discussed earlier in this document. Higher levels of antimony enhance these effects. An additional advantage is that the cathodes obtained in the subsequent electrolysis step performed on the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, can be easily incorporated in the process of recovering the main product in the form of high purity tin together with the main product in the form of solid lead, since the main product in the form of solid lead allows a significant level of antimony and since antimony is an element that contributes greatly to the desired properties of the main product in the form of solid lead as opposed to the main products in the form of soft lead with higher purity. The inventors have found that a further increase in the level of antimony concentration in anodes to be cast from the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, can be easily achieved by introducing a small amount of Pb/Sn concentrate, such as, for example, a small amount of solid lead major product from the steps following the process of the present invention. The inventors have found that the level of antimony (together with bismuth) which is most advantageous for very good electrolysis operations can be obtained in this way without difficulty in anodes that are cast from the metal composition of the present invention. The authors prefer that the level of antimony together with bismuth in these anodes was at least 1.0 wt.% and, if necessary, at most 1.5 wt.%

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at most 4.00 wt.% or even at most 3.5 wt.% antimony, preferably at most 3.00 wt%, more preferably at most 2.50 wt%, even more preferably at most 2.00 wt%, preferably at most 1.75 wt%, 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 0.75 wt.% antimony. This provides the advantage in the subsequent electrolysis step that the antimony does not dissolve in the electrolyte but remains in the anode sludge and promotes better adhesion of the anode sludge to the anodes so that the anode sludge can be recovered by simple mechanical scraping off the used anode. Another advantage of less antimony is that the anode sludge will have a higher concentration of silver metal to be recovered and therefore more suitable for upgrading the silver to industrial grade silver as the main product.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, is a liquid melt. This provides the advantage that the composition does not need to be melted again before it can be cast to produce anodes for the electrolysis step described above in this document, on which Sn/Pb and silver cathodes can be formed. can be recovered in higher concentrations as part of the anode sludge generated in the cell.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at least 0.05 wt.% and at most 0.5 wt.% arsenic, preferably at least 0.06 wt.%, more preferably at least 0.07 wt.%, even more preferably at least 0.08 wt.%, preferably at least 0.09 wt.%, preferably at least 0.10 wt.%, more preferably at least 0.11 wt.%, even more preferably at least 0.12 wt.% arsenic and optionally at most 0.45 wt.% arsenic, preferably at most more than 0.40 wt%, more preferably at most 0.35 wt%, even more preferably at most 0.30 wt%, preferably at most 0.25 wt%, more preferably at most 0.200 wt%, even more preferably the most greater than 0.175 wt%, preferably at most 0.150 wt%, more preferably at most 0.125 wt% arsenic. The authors have found that limited levels of arsenic are acceptable in the further processing of the metal composition according to the present invention. The acceptability of arsenic in the metal composition of the present invention, which is preferably produced as the first liquid product with a higher concentration of silver withdrawn from the crystallizer in the process of the present invention, makes it less stringent and broadens the acceptance criteria for the prior processes from which the metal composition is produced. In the subsequent electrolysis of the anodes, which are cast from the metal composition of the present invention, optionally with some added Pb/Sb concentrate as discussed above, most of the arsenic will tend to remain with the anode sludge and be removed from the process as part of the anode sludge. The authors prefer that the level of arsenic remain below the specified upper limit, since this provides less reduction in the concentration of silver in the anode sludge and makes this anode sludge more suitable for upgrading the silver contained in it to the quality of the main product in the form of silver suitable for industrial use.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, further contains at least 0.05 wt.% and at most 0.6 wt. % copper, preferably at least 0.07 wt.%, more preferably at least 0.10 wt.%, even more preferably at least 0.12 wt.%, preferably at least 0.15 wt.% copper , preferably at least 0.20 wt.%, more preferably at least 0.25 wt.%, even more preferably at least 0.30 wt.% copper and optionally at most 0.55 wt.% copper, preferably at most 0.50 wt.%, more preferably at most 0.48 wt.%, even more preferably at most 0.45 wt.%, preferably at most 0.40 wt.%, more preferably at most 0.350 wt. %, even more preferably about at most 0.325 wt.%, preferably at most 0.300 wt.%, more preferably at most 0.250 wt.% copper. The acceptability of copper in the metal composition of the present invention, which is preferably produced as the first liquid product with an increased concentration of silver withdrawn from the mold in the process of the present invention, provides the advantage that for the upstream process in which this composition is produced, Feed streams containing copper, such as by-products of copper refining, may be acceptable. The prior process in which the metal composition of the present invention is produced is preferably part of a general process including the production of refined copper, refined tin and refined lead, and the metal composition of the present invention is preferably a by-product from such a process to recover silver entering the general technological process. However, the authors prefer to limit the presence of copper in the metal composition according to the present invention, since copper leads to increased costs in the subsequent stages of the process. For example, the excessive presence of copper is believed to interfere with the benefits described above of having antimony (and bismuth) in the metal composition of the present invention. If the copper content of the steps prior to the preparation of the metal composition according to the present invention is above the specified upper limit, some of the copper can be removed by adding sulfur, which forms dross containing copper sulfides, which can be easily removed from the surface and returned for processing to the previous a step in the pyrometallurgical process, and which can ensure that a composition is left that satisfies all the conditions specified for the metal composition according to the present invention.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at least 0.0030 wt.% and at most 0.0500 wt.% nickel, preferably at least 0.0050 wt.%, more preferably at least 0.0075 wt.%, even more preferably at least 0.0100 wt.%, preferably at least 0.0125 wt.%, preferably at least 0.0150 wt.%, more preferably at least 0.0175 wt.%, even more preferably at least 0.0200 wt.% nickel and optionally at most 0.0450 wt.% nickel, preferably at most greater than 0.0400 wt.%, more preferably at most 0.0350 wt.%, even more preferably at most 0.0325 wt.%, preferably at most 0.0300 wt.%, more preferably at most 0.0275 wt. %, more its preferably at most 0.0250 wt.%, preferably at most 0.0225 wt.%, more preferably at most 0.0200 wt.% nickel. The authors prefer to allow a limited amount of nickel in the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, since this creates the possibility that for the process in which given composition, starting materials that contain nickel, such as by-products of copper refining and/or nickel refining, will be acceptable. The presence of nickel is preferably limited so as not to create excessive costs in the subsequent processing of the metal composition, for example, in the electrolysis stage, in which nickel will tend to dissolve in the electrolyte rather than deposited on the cathode. This may lead to an increase in the nickel content of the electrolyte, which may necessitate regulation by providing an electrolyte flow drained to control the properties of the electrolyte in the electrolysis step, as described in WO 2019/219821 A1.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at least 0.0010 wt.% and at most 0.40 wt.% bismuth, preferably at least 0.0020 wt.%, more preferably at least 0.0030 wt.%, even more preferably at least 0.0040 wt.%, preferably at least 0.0060 wt.%, preferably at least 0.0070 wt.%, more preferably at least 0.0085 wt.%, even more preferably at least 0.0100 wt.% bismuth and optionally at most 0.30 wt.% bismuth, preferably at most greater than 0.200 wt%, more preferably at most 0.150 wt%, even more preferably at most 0.1000 wt%, preferably at most 0.0750 wt%, more preferably at most 0.0500 wt%, still morepreferably at most 0.0400 wt%, preferably at most 0.0300 wt%, more preferably at most 0.0250 wt% bismuth. The inventors have found that limited amounts of bismuth are acceptable, which means that bismuth-containing feedstocks may be acceptable for the prior art. In addition, the inventors have found that bismuth is also desirable in the metal composition of the present invention, which is preferably produced as the first liquid product with an increased concentration of silver withdrawn from the crystallizer in the process of the present invention, as it is believed to contribute to the beneficial effect of antimony. when the metal composition according to the present invention is used as a starting material for the electrolysis step described above. The inventors prefer to meet this upper limit because bismuth remains in the anode sludge and therefore less bismuth provides the advantage that the anode sludge will have a higher concentration of silver metal to be recovered, making the anode sludge more degree suitable for upgrading the quality of the silver contained in it to the quality of the main product in the form of silver, suitable for industrial use.

The inventors have also found that bismuth may end up in the main product in the form of tin, obtained from a metal composition, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the crystallizer in the process according to the present invention, and in which limited levels of bismuth content. In addition, the low amount of bismuth present in the final product as tin provides the advantage of lowering the temperature at which a phenomenon referred to as "tin plague" can occur. Tin plague is an autocatalytic transformation of the white beta modification of homogeneous solid tin to gray alpha tin in the form of a powder, which can give the surface of white tin a haze with a gray tint and, possibly due to the autocatalytic nature of the transformation, can even lead to physical destruction of a tin metal object to a gray powder.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at most 1.0 wt.% iron, preferably at most 0.1 wt. %, more preferably at most 0.01 wt.%, even more preferably at most 0.0050 wt.%, even more preferably at most 0.0010 wt.% iron.

The inventors have found that limiting the iron content as indicated provides a significant advantage for the case where the metal composition of the present invention, which is preferably produced as the first liquid product with increased silver concentration withdrawn from the mold in the process of the present invention, is used for casting anodes as starting material for the electrolysis step discussed above. The authors found that iron dissolved in the electrolyte at this stage causes a significant reduction in energy efficiency due to the fact that it causes part of the electric current passing through the cell to not contribute to the movement of lead and tin cations from the anode to the cathode. Without wishing to be bound by this theory, the authors believe that iron cations in the electrolyte can easily change valence ( valence ) (also referred to as valency ) presumably due to the Fe ²⁺ → Fe ³⁺ + e ^- half-transformation occurring at the anode, and reverse semi-transformation of Fe ³⁺ + e ^- → Fe ²⁺ at the cathode after the movement of the Fe ³⁺ cation to the cathode, after which the Fe ²⁺ cation can return to the anode.This mechanism can explain the observational results that with significant amounts of iron in the electrolyte, part of the electric current can pass through the electrolyzer without promoting the movement of lead and/or tin cations.

The authors also found that an additional, but not contributing to the desired result, electric current is required to maintain an identical cathode productivity due to the presence of iron in the anodes and, therefore, also in the electrolyte. The increased current causes the voltage across the cell to rise as well as a rapid rise, which leads to increased levels of contaminants in the cathode and results in the maximum allowable level being reached more quickly. More current also generates more heat in the cell and possibly hot spots, which causes other problems. As a result, the current density also increases at the same performance, which causes an increase in its "contribution" to the cathode contamination. More details regarding the problems arising from the presence of iron are described in WO 2019/219821 A1.

When iron passes from the anode to the electrolyte due to its dissolution, iron causes an increase in the density and viscosity of the electrolyte, which affects the mechanisms of mass and heat transfer in the cell, for example, the movement of given cations on their way to the cathode. The high content of Fe in the anode and therefore also in the electrolyte leads to an increase in the resistance that these given cations must overcome on their way to the cathode.

It is for this reason that the metal composition according to the present invention must have an iron content at a level that is below a predetermined upper limit.

In an embodiment, the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the mold in the method according to the present invention, contains at least 0.0005 wt.% gold, preferably at least 0.0010 wt.%, more preferably at least 0.0020 wt.%, even more preferably at least 0.0030 wt.%, preferably at least 0.0040 wt.% gold, more preferably at least 0.0050 wt. .%, even more preferably at least 0.0060 wt.%, even more preferably at least 0.0070 wt.%, preferably at least 0.0080 wt.%, more preferably at least 0.0085 wt. %, even more preferably at least 0.0090 wt.%, even more preferably at least 0.0100 wt.% gold and, if necessary, at most 0.0500 wt.%, preferably at most 0.0250 wt.%, more preferred Preferably at most 0.0200% by weight, even more preferably at most 0.0175% by weight of gold. The inventors have found that gold present in small amounts in the pyrometallurgical processing of non-ferrous metals may be concentrated in the product withdrawn from the described fractional crystallization step as part of the process according to the present invention, and therefore may be present in the metal composition according to the present invention, which is preferably obtained as the first liquid product with an increased concentration of silver withdrawn from the crystallizer in the method according to the present invention. Gold is a precious metal and can be recovered along with silver and other precious/noble metals that may be present in this composition, in particular as part of the anode sludge generated during the electrolysis stage, in which this composition can be treated as source material.

In an embodiment of the method according to the present invention, the amount of lead in the mixture with black tin as raw material fed to the crystallization step is at least 0.15% by weight, preferably at least 0.20% by weight, more preferably at least 0.30 wt.%, even more preferably at least 0.40 wt.%, even more preferably at least 0.50 wt.%, preferably at least 0.60 wt.%, more preferably at least 0 .70 wt.%, even more preferably at least 0.80 wt.%, preferably at least 0.90 wt.% and more preferably at least 1.00 wt.%. Lead is a contributing factor to the fractional crystallization step and serves as a solvent for the silver that it is desired to remove at this stage from the main crude tin stream. The silver tends to stay with most of the lead and end up in the effluent, and the effluent composition approaches a eutectic composition of 38.1 wt% Pb and 61.9 wt% Sn. Ensuring that Pb is present at a concentration corresponding to this lower limit facilitates the feasibility of the fractional crystallization step, for example by ensuring that sufficient liquid phase is guaranteed in the crystallizer stages where good and direct contact between liquid and crystals is desired to ensure effective separation.

In an embodiment of the process according to the present invention, the amount of tin mixed with crude tin feed to the crystallization step is at least 65% by weight, preferably at least 70% by weight, more preferably at least 80% by weight. , even more preferably at least 90 wt.%, preferably at least 92 wt.% and more preferably at least 92.0 wt.%. Ensuring that this lower limit is met ensures that the mold will function on the proper side of the eutectic composition of the lead/tin mixture. This ensures that an effluent with a composition that approaches the eutectic composition is obtained and that most of the lead and therefore silver is recovered from the effluent/drain from the crystallization step and not from the crystal fraction side.

In an embodiment of the method according to the present invention, the black tin mixture contains at most 6.5 wt.% Pb, preferably at most 6.0 wt.%, more preferably at most 5.5 wt.%, even more preferably at most 5, 25 wt%, preferably at most 5.00 wt%, more preferably at most 4.90 wt%, even more preferably at most 4.80 wt%, preferably at most 4.00 wt%, more preferably at most 3.00 wt.%, even more preferably at most 2.00 wt.% Pb, preferably at most 1.50 wt.% Pb. The inventors have found that with lower amounts of lead in the raw material as a mixture with crude tin fed to the crystallization step, the amount of by-product withdrawn can be kept smaller and the concentration of silver in the withdrawn product can be kept higher. This provides the advantage that silver can be recovered from feedstocks having a lower silver concentration while still producing an effluent that has a silver concentration high enough to allow efficient and economical recovery of silver from it. The lower volume of the effluent and the higher silver content also contribute to the efficiency and economy of the process steps for recovering silver from the effluent.

In an embodiment of the method according to the present invention, the concentration of lead in the mixture with crude tin is at least 3.0 times the concentration of silver in the mixture with crude tin, preferably at least 4.0 times, more preferably at least 5.0 times, even more preferably at least 6.0 times, and even more preferably at least 7.0 times, the concentration of silver mixed with black tin. The authors found that maintaining this lower limit on the lead/silver ratio avoided that the composition of the withdrawn product would approach the eutectic composition in the phase diagram of the ternary system of lead/tin/silver.

In an embodiment of the method according to the present invention, the black tin mixture contains at least 10 ppm. silver (Ag) by weight, preferably at least 20 ppm. by weight, more preferably at least 25 ppm. by weight, even more preferably at least 30 ppm. by weight, even more preferably at least 50 ppm. by weight, preferably at least 100 ppm. by weight, more preferably at least 200 ppm. by weight, even more preferably at least 300 ppm. by weight, even more preferably at least 500 ppm. by weight, preferably at least 750 ppm. by weight, more preferably at least 1000 ppm. by weight, even more preferably at least 1100 ppm. by weight, even more preferably at least 1200 ppm. silver by weight and optionally at most 0.85 wt.% silver, preferably at most 0.80 wt.%, more preferably at most 0.75 wt.%, even more preferably at most 0.70 wt.%, still more preferably at most 0.65 wt%, preferably at most 0.60 wt%, more preferably at most 0.55 wt%, even more preferably at most 0.50 wt%, even more preferably at most 0 45 wt.%, preferably at most 0.40 wt.%, more preferably at most 0.35 wt.%, even more preferably at most 0.30 wt.%, even more preferably at most 0.25 wt.% , preferably at most 0.20 wt%, more preferably at most 0.175 wt% or at most 1750 ppm. by weight, even more preferably at most 1600 ppm. by weight, even more preferably at most 1500 ppm. by weight. The higher silver content in the mixture with crude tin feed to the crystallization stage provides the advantage that more silver will be available for recovery and that the product withdrawn from the crystallizer may contain more silver and , therefore, not only has a higher economic value, but also allows a more economical and more efficient recovery of silver from it. Ensuring that the upper limit of silver content is met provides the advantage that the composition of the effluent is less at risk of approaching the eutectic composition in the Pb/Sn/Ag ternary phase diagram. The upper limit of the content of silver in the mixture with crude tin also provides the advantage that it allows a significant increase in the concentration of silver from the source material to the product withdrawn from the mold, so that a raw material having a lower silver content may be acceptable for the process, that is, a feedstock that may have a greatly reduced concentration of Ag.

In an embodiment of the method according to the present invention, the black tin mixture contains at least 0.1 wt.% antimony (Sb), preferably at least 0.2 wt.%, more preferably at least 0.5 wt.%, still more preferably at least 1.0 wt.%, preferably at least 1.2 wt.%, more preferably at least 1.5 wt.%, even more preferably at least 2.0 wt.% antimony and when need at most 6.0 wt.% antimony, preferably at most 5.0 wt.%, more preferably at most 4.0 wt.% antimony. This provides the advantage that the process of the present invention, as well as prior processes that produce a mixture with black tin as the starting material for the crystallization step, will be more versatile in terms of acceptability of raw materials. In addition, the inventors have found that most of the antimony tends to remain with the tin during the crystallization step, and the presence of antimony has the advantage that it causes an increase in the melting point of the resulting crystals, which promotes separation in the mold and provides a clearer separation between Pb/Ag in the effluent and Sn/Sb in the crystals.

In an embodiment of the method according to the present invention, the first product with an increased concentration of tin contains at least 0.05 wt.% lead, preferably at least 0.10 wt.%, more preferably at least 0.15 wt.%, even more preferably at least 0.20 wt.% lead. This provides the advantage that this stream is more suitable as a feedstock for a distillation step, in which lead and antimony can be removed by evaporation from the main tin stream, and in which the more volatile lead facilitates the evaporation of antimony by diluting the steam phases in the distillation step. Thus, lead serves as a kind of carrier for antimony. The inventors have found that, as will be shown elsewhere in this document, lead in combination with antimony and after a subsequent distillation step produces a distillate product which is suitable for the production of solid lead as the main product.

In an embodiment of the method according to the present invention, the first product with an increased concentration of tin is obtained continuously. This provides the advantage that the quality of the first product with increased tin concentration is more constant and stable over time and that subsequent steps in which the product is further processed can be performed more efficiently and economically.

In an embodiment of the method according to the present invention, the entire fractional crystallization step is performed continuously. This provides the advantage that the quality of the products obtained from the fractional crystallization step is more constant and stable over time, so that further processing of these products can be carried out more efficiently and more economically.

In an embodiment of the method according to the present invention, the first liquid product with an increased concentration of silver is returned partially and/or temporarily to the starting material supplied to the fractional crystallization step. This provides the advantage that the enrichment factor for silver, i.e., the concentration ratio, which is the ratio of the concentration of silver in the resulting effluent removed from the process to the concentration of silver in the fresh feed to the process, is further increased. This provides the advantages already explained in that (i) a feedstock that has a lower silver concentration becomes acceptable for the process of the present invention, and (ii) a more economical and efficient further processing of the withdrawn product is provided.

In an embodiment of the method according to the present invention, the fractional crystallization step comprises the use of at least 4 crystallizer stages, preferably at least 8, more preferably at least 10, even more preferably at least 12, even more preferably at least 16, preferably at least at least 20, more preferably at least 24 mold stages. This provides the advantage that the crystallizer can provide a clearer separation between Pb/Ag in the effluent and Sn/Sb in the crystals. This further provides the advantage of a higher degree of increase in the concentration of silver in the composition of the withdrawn product relative to the source material, which provides the corresponding benefits explained elsewhere in this document.

In an embodiment of the method according to the present invention, the crystallizer used in the fractional crystallization step comprises a feed stage for receiving raw material fed into the crystallizer, and the crystallizer further comprises at least one crystallizer stage and preferably at least 2 stages between the feed stage and each of the elements of the mold intended for the release of the product. This provides the advantage that the compositions of both products will differ to a greater extent from the composition of the starting material. This provides the additional benefit of greater operational flexibility. An additional advantage is that this makes it easier to control the temperature profile throughout the crystallization step, resulting in a clearer separation.

In an embodiment of the method according to the present invention, the temperature profile at all stages in the fractional crystallization step is in the range of 180-270°C. The authors found that this temperature range is sufficient to provide a desired separation between Pb/Ag in the withdrawn product and Sn and possibly Sb in the product obtained on the side of the crystalline fraction in the crystallization stage. The minimum temperature in the mold is preferably at least 183°C, more preferably at least 185°C, even more preferably at least 187°C, even more preferably at least 190°C, preferably at least 193°C, more preferably at least 196°C. If necessary, the maximum temperature in the mold is at most 265°C, preferably at most 260°C and more preferably at most 255°C. These temperature setpoints provide the advantage of less temperature difference across the entire mold, so that less heating and/or less cooling will be required.

In an embodiment of the method according to the present invention, the temperature difference between two adjacent stages in the fractional crystallization stage, excluding the feeding stage and the final stage, is at most 20°C, preferably at most 15°C, more preferably at most 10°C. This has the advantage that less cooling and/or less heating needs to be provided, so that fewer heat exchange surfaces need to be provided, and the quality of the separation/separation is also improved.

In an embodiment of the method according to the present invention, the fractional crystallization step is carried out in at least 2 crystallizers in series, wherein the product coming from the crystalline fraction zone in the upstream mold is fed into the downstream mold, either being fed completely into the feed stage in the downstream mold, or only its first part is fed to the feed stage in the subsequent crystallizer and its second part is fed to the second stage of the subsequent crystallizer different from the feeding stage, this second stage being selected from the stages located between the feeding stage and the final stage on the side of the crystalline fraction in the subsequent the mold, this second stage is preferably separated from the feed stage by at least one and preferably two or three intermediate stages. The authors found that this configuration is highly desirable and can provide better separation. In addition, this configuration provides additional flexibility in choosing where to send intermediate streams or streams returned for processing.

In an embodiment of the process according to the invention, the product obtained on the liquid fraction side of the downstream mold is at least partially and preferably completely at least temporarily returned to the downstream mold, if necessary in the feed stage, but preferably in the second stage, which is selected from the stages located between the feed stage and the final stage on the side of the crystalline fraction in the previous mold, while this second stage is preferably separated from the final stage by at least one and preferably two or three intermediate stages. This provides the advantage that less lead can accumulate in the downstream mold due to possible carryover of lead that has been recycled with the effluent coming from the downstream mold to the upstream mold and wetting of upstream crystallizer feed into the downstream mold. crystallizer.

In an embodiment of the method according to the present invention, the black tin mixture further comprises at least 1 ppm by weight of at least one metal selected from copper, iron, bismuth, nickel, zinc, gold, indium and arsenic. The presence of traces of copper and iron is a strong indication that the black tin mixture was obtained as a by-product in the production of copper through a pyrometallurgical process. The admissibility of small amounts of the listed metals ensures the versatility of the previous technological processes in relation to the processed raw materials, while in these processes a mixture is obtained with black tin as a raw material for the crystallization stage. The inventors have found that many of the metals listed tend to end up at least partially in the effluent, sometimes even being concentrated in the effluent and therefore being at least partially removed from the main tin stream, from which it can then be easier to obtained the main product in the form of high-purity tin.

In an embodiment of the method according to the present invention, the black tin mixture contains at least 99.0 wt.% tin, lead, antimony and silver together, preferably at least 99.1 wt.%, more preferably at least 99.2 wt. .%, even more preferably at least 99.3 wt.%, even more preferably at least 99.4 wt.%, preferably at least 99.5 wt.%, more preferably at least 99.6 wt. %, even more preferably at least 99.7 wt.% tin, lead, antimony and silver together. This provides the advantage that the black tin mixture contains less other materials which may possibly cause additional costs associated with further processing of the crystallization products and/or may be a contaminant in at least one of the main products. that can be obtained from this mixture.

In an embodiment of the method according to the present invention, the black tin mixture is at least partially obtained as the first bottom product obtained in the first distillation step, in which lead (Pb) is removed from the molten solder mixture by evaporation, whereby the first product is obtained as a distillate product. concentrated stream of lead. The inventors have found that the starting material fed to the mold can be very usefully obtained as an underproduct resulting from the vacuum distillation of a solder mixture from which most of the lead has been removed by evaporation distillation. The authors prefer to carry out this first distillation step as described in WO 2018/060202 A1. In an embodiment of the method according to the present invention, a suitable fresh starting material is also added as additional starting material to the crystallization step.

In an embodiment of the process according to the present invention, at least one product obtained on the liquid fraction side in at least one crystallizer in the fractional crystallization step is at least partially returned to the feedstock fed to the first distillation step, this product preferably being is the liquid effluent from the mold, which is the earliest of the molds through which the tin stream passes through the fractional crystallization step. The inventors have found that this provides an additional opportunity to reduce the presence of lead in the fractional crystallization step so that the amount of the resulting effluent to be removed from the silver recovery process can be reduced and the silver concentration can be further increased. In addition, this return for processing expands the list of raw materials that are acceptable to include materials that have a lower silver content.

In an embodiment of the process according to the present invention, the first bottom product obtained from the first distillation step contains at least 0.1 wt.% lead, preferably at least 0.15 wt.% or even at least 0.20 wt.% , more preferably at least 0.30 wt.%, even more preferably at least 0.40 wt.%, even more preferably at least 0.50 wt.%, preferably at least 0.60 wt.%, more preferably at least 0.70 wt.%, even more preferably at least 0.80 wt.%, preferably at least 0.90 wt.% and more preferably at least 1.00 wt.%. This provides the advantage that the first bottom product is even more suitable as a feedstock for the fractional crystallization step and meets the desired characteristics described elsewhere for the feedstock for the fractional crystallization step.

In an embodiment of the process according to the present invention, the first silver concentrated liquid effluent is subjected to a fourth distillation step in which lead is removed by evaporation and enters a fourth concentrated lead stream obtained as an overhead product, whereby a fourth distillation bottom product is obtained. The inventors have found that the concentration of silver in the first liquid silver concentrated effluent can easily be further increased by removing most of the lead contained therein by vacuum distillation. The inventors have found that this vacuum distillation can be easily carried out in a batch mode, which is useful if the amount of starting material is limited. In addition, the authors found that the quality of the upper condensate obtained from this fourth stage of vacuum distillation can be ensured, which is comparable to the first concentrated stream of lead obtained from the first stage of distillation, and this condensate can be mixed with this stream and subjected to further processing. together with it to obtain the main product in the form of soft lead, as explained elsewhere in this document. The inventors have found that by this fourth distillation step, the silver concentration in the fourth bottom product can be substantially increased compared to the silver content of the feedstock fed to the fourth distillation step.

In an embodiment of the process according to the present invention, the fourth distillation bottom product is subjected to a fractional crystallization step, which produces a second effluent with increased silver concentration on the liquid fraction side and a second product with increased tin concentration on the crystalline fraction side. The inventors have found it useful to reduce not only the level of lead, but also the level of tin in the silver containing stream before subjecting the stream to further processing to recover the silver. The authors found that another crystallization step is more than appropriate because it allows most of the tin to be withdrawn to the second product with increased tin concentration on the side of the crystalline fraction, while leaving a much smaller volume of the second product with increased concentration of silver, intended for additional processing for the extraction of silver. The second tin-enhanced product may still contain a small amount of lead and is suitable for blending with crude tin as a feedstock for the fractional crystallization step resulting in the first tin-enhanced product.

In an embodiment of the method of the present invention, a first silver concentrated liquid effluent or a second silver concentrated liquid effluent is used as a starting material for casting at least one anode which is subjected to an electrolytic refining step to produce a leaded cathode product. and tin and silver rich anode sludge, preferably anode sludge adhering to and separated from the used anode by mechanical means. The authors found that this stage is very useful in order to obtain a stream in which the silver will be at the end with an additional increased concentration, that is, the anode sludge obtained from this electrolytic refining stage and containing approximately 20 wt.% silver, which is qualified as the main product containing silver. The authors indicate that technical solutions for this electrolytic refining step, such as using an electrolyte based on hexafluorosilicic acid (H ₂ SiF ₆ ), fluoroboric acid and/or phenylsulfonic acid, a temperature of approximately 35-40°C, a current density in the range of 140 -200 A/m ² and electrode spacing of approximately 100 mm are known in the art. In addition, the authors indicate that the electrolysis step is particularly advantageous when the anode slurry adheres to the used anode, so that the used anode can be removed from the bath and the anode sludge can be removed from the used anode by mechanical means, for example by scraping.

In an embodiment of the method according to the present invention, this at least one anode used in the electrolytic refining step to obtain a cathode product with an increased concentration of lead and tin contains at least 0.5 wt.% antimony, preferably at least 1.0 wt. .% and more preferably at least 1.5 wt.% antimony. The inventors have found that this presence of antimony provides the advantage that the anode sludge remains adhering to the anode rather than being dispersed in the electrolyte. This facilitates the extraction of the anode sludge. The inventors have found that if there is not enough antimony in the anode casting stream, the preferred level of antimony can be easily achieved by adding an appropriate amount of Pb/Sb concentrate to the stream, such as some of the main product in the form of a solid lead, which is obtained as one of the final main products from the general technological process, including the described method/process according to the present invention.

In an embodiment of the method according to the present invention, the molten solder mixture that is fed to the first distillation step is obtained by pre-treating a crude solder composition containing at least 90 wt.% tin and lead together. The inventors have found that such crude solder compositions are readily available, for example, as a by-product in the pyrometallurgical production of copper, for example from recycled materials. The authors prefer to perform this pre-treatment as described in WO 2018/060202 A1.

In an embodiment of the method according to the present invention, the raw solder composition contains at least 0.16 wt.% and optionally at most 10 wt.% chromium (Cr), manganese (Mn), vanadium (V), titanium (Ti), tungsten (W), copper (Cu), nickel (Ni), iron (Fe), aluminum (Al) and/or zinc (Zn) together, and wherein the pretreatment includes the step of cooling the raw solder composition to a temperature of at most 825 °C, to obtain a bath containing the first floating dross, which under the influence of gravity becomes floating on top of the first liquid phase of the molten metal. This step provides the advantage of removing most of the copper that may be present in the raw solder composition.

In an embodiment, the method according to the present invention further comprises the step of adding a compound selected from an alkali metal and/or alkaline earth metal, or a chemical compound containing an alkali metal and/or alkaline earth metal, to the first liquid phase of the molten metal to form a bath containing a second pop-up dross , which under the action of gravity becomes floating on top of the second liquid phase of the molten metal, and removing the second floating dross from the second liquid phase of the molten metal to obtain a molten solder mixture. This step provides the advantage of removing most of the zinc that may be present in the raw solder composition.

In an embodiment, the method according to the present invention further includes the step of removing the first pop-up dross from the first liquid phase of the molten metal. This dross can be easily returned for processing to the appropriate stage of the preceding pyrometallurgical process so that the valuable metals contained therein can be recovered.

In an embodiment of the method according to the present invention, at least one product obtained on the liquid fraction side in at least one mold in the fractional crystallization step is at least partially returned to the raw material fed to the raw solder pretreatment step. This provides the advantage that the concentration of copper in the process according to the present invention, which may have increased due to the fact that copper enters the raw material fed to the first stage of distillation, and may be in the material subjected to the processing stage of fractional crystallization, again is reduced by allowing the copper to be removed from the material to be processed along with the first and/or second floating dross separated in the raw solder pretreatment step.

In an embodiment of the method according to the present invention, the process for producing a crude solder composition includes a metal smelting step and at least one of the first and/or second pop-up dross is returned for processing to the smelting step, preferably both drosses are returned for processing to the smelting step. This provides the advantage that valuable metals of interest such as Cu, Ni and/or Zn as well as entrained/entrained Sn, Pb, Sb and/or Ag can be recovered and upgraded to an appropriate quality. main product.

In an embodiment of the method according to the present invention, the molten solder mixture that is fed into the first distillation step contains, on a dry weight basis:

- more lead than tin;

- at most 0.1% chromium (Cr), manganese (Mn), vanadium (V), titanium (Ti) and tungsten (W) together;

- at most 0.1% aluminum (Al);

- at most 0.1% nickel (Ni);

- at most 0.1% iron (Fe); and

- at most 0.1% zinc (Zn).

This provides the advantages that (i) the pre-treatment process is facilitated because the main solder stream has a high liquid density, which helps to provide a clear separation between any floating dross and the liquid phase below it, and that (ii) the possibility of uninterrupted performance of the first stage of distillation, that is, with a small risk of the formation of solid intermetallic compounds during distillation, which are deposited on the internal surfaces of the equipment and impair the passage of fluids through the distillation equipment.

In an embodiment of the method according to the present invention, the molten solder mixture which is fed into the first distillation step contains, on a dry weight basis, by weight, at least 1 ppm. copper by weight and at most 5000 ppm. copper by weight.

The inventors have further found that potentially harmful metals, and in particular copper, do not have to be completely removed from the solder mix to ensure that the solder mix is suitable for vacuum distillation. The inventors have, for example, found that the severity of the identified problems can be reduced to a practical and economically acceptable level, when small amounts of copper remain present in the solder source material fed to the first stage of distillation. This result provides the advantage that solder streams can be treated, which are formed as a by-product in the recovery of copper from primary and/or secondary raw materials, in particular from secondary raw materials, and more importantly from raw materials containing materials disposed of at the end of their useful life.

In an embodiment of the present invention, the molten solder mixture that is fed to the first distillation step contains at least 0.0001% by weight of sulfur (S). The inventors have also found that there is no need to bring sulfur levels to very low levels, such as levels below the detection limit of 1 ppm. by weight. On the contrary, the presence of sulfur in the mixture of metals provides a technical advantage.

The inventors have found that sulfur bonds quite easily with copper to form copper sulfide (such as CuS) and that copper sulfide easily separates by gravity from a mixture of liquid metals containing the two main components in the process, i.e., tin and lead. Therefore, the presence of sulfur can assist in the removal of Cu at each step of the process, which is designed to separate copper Cu or which separates Cu in the pop-up dross.

Therefore, the presence of sulfur in the metal mixture according to the present invention is a reliable indicator that the metal mixture according to the present invention was obtained as a by-product from the copper production process. As a result, there is a possibility that the starting material for the first distillation step may contain measurable amounts of copper as impurities, for example, at the specified level. The copper content of such feed streams can be reduced by a wide variety of possible process steps, of which Cu binding via S is only one process. Any sulfur treatment to remove Cu is likely to leave measurable traces of S in the metal mixture. Therefore, the presence of S in the metal mixture according to the present invention is closely related to the fact that the metal mixture was obtained as a by-product in the production of copper, preferably including a step involving treatment with sulfur or a suitable sulfur-containing compound.

In addition, the inventors have found that the presence of sulfur in the feed to the first distillation step does not pose any problems, provided that some of the indicated amount of copper is also present. The presence of S may assist in subsequent purification steps to remove Cu from less noble metal streams on their way to commercially acceptable quality. Therefore, the presence of S in the mixture of metals according to the present invention is preferred, with the preferred effects occurring in subsequent steps.

In an embodiment of the method according to the present invention, the fourth concentrated lead stream obtained as a distillate product in the fourth distillation step is combined with the first concentrated lead stream to obtain a fifth concentrated lead stream. The inventors have found that the fourth concentrated lead stream obtained by treating the liquid effluent obtained from the fractional crystallization step can be easily combined with the first concentrated lead stream obtained as distillate from the first distillation stage and can lead to a higher yield of the main product. in the form of soft lead without significant additional effort.

In an embodiment, the method of the present invention further includes the step of removing at least one contaminant selected from metallic arsenic, tin, and antimony from a concentrated lead stream selected from a first concentrated lead stream, a fourth concentrated lead stream, and a fifth concentrated lead stream, to obtain the main product in the form of purified soft lead. The authors have found that any of the concentrated lead streams listed are highly suitable for producing base soft lead products that meet the requirements of the important end uses of such products, with limited chemical refining steps, limited chemical consumption, and limited processing costs. any by-products. The inventors have found that using means known in the art, soft lead major product can be obtained from any of the first, fourth and fifth concentrated lead streams by removing arsenic, tin and/or antimony from them. The inventors preferably carry out this soft lead refining step as described in the co-pending patent application EP 19154606.8.

In an embodiment of the present invention, the at least one contaminant is removed by treating the concentrated lead stream at a temperature that is less than 600° C. with a first base and a first oxidizing agent, resulting in a third pop-up dross containing the metalate compound of the respective contaminant metal. followed by separation of the dross from the purified soft lead stream or purified soft lead product stream.

In this refining of soft lead, the crude Pb feedstock is preferably contacted with a combination of NaOH and NaNO ₃ . Chemical processes that are provided with these chemical reagents can be represented by the following reactions:

5 Pb + 6 NaOH + 4 NaNO ₃ → 5 Na ₂ PbO ₃ +2 N ₂ +3 H ₂ O (I) 5 Na ₂ PbO ₃ +4 As + 2 NaOH → 4 Na ₃ AsO ₄ +5 Pb + H ₂ O (II) Na ₂ PbO ₃ + Sn → Na ₂ SnO ₃ + Pb (III) 5 Na ₂ PbO ₃ +3 H ₂ O + 4 Sb → 4 NaSbO ₃ +6 NaOH + 5 Pb (iv)

The key to these chemical processes is to enable the formation of an intermediate sodium plumbate (Na ₂ PbO ₃ ) via reaction (I). This intermediate plumbate is capable of reacting with impurities As, Sn and Sb in accordance with the corresponding reactions (II) - (IV) and each time "captures" them in the corresponding compound in the form of sodium metalate, providing the release of Pb again in a free form. The compounds formed in the form of sodium metallates are sodium arsenate, sodium stannate and sodium antimonate, respectively.

The corresponding compounds in the form of sodium metallates accumulate in the floating phase, commonly referred to as "dross" or sometimes also "slag". The terms are often used interchangeably, although the term "slag" is generally used for the liquid phase, while "dross" is generally used to refer to a phase with a less fluid, more solid consistency. The term "slag" is more commonly used when it comes to the production of non-ferrous metals with a high melting point, such as copper, and therefore usually refers to a fluid, often containing mainly metal oxides. The term "dross" is used more frequently when referring to lower melting point non-ferrous metals such as Sn, Pb, Zn, Al, which are often in a solid or dusty form. However, the distinction between these two terms related to consistency is not always clear.

The dross from the soft lead refining step may be skimmed off the surface and may be further processed to recover at least some of its constituents.

In an embodiment of the method according to the present invention, the third pop-up dross contains at most 1.0 wt.% chlorine, preferably at most 1.0 wt.% halogens in total.

The inventors have found that the said low content of chlorine and/or other halogens in the third pop-up dross makes the third pop-up dross more suitable to be introduced into a step of a prior pyrometallurgical process, preferably a process step in which at least one of the sodium metallates is stannate ( compound with Sn), antimonate (compound with Sb) and arsenate (compound with As), can be reduced to obtain the corresponding Sn, Sb or As metal, preferably also together with Pb, finally in its elemental form.

The third pop-up dross is more acceptable at the stage of the pyrometallurgical process due to the limited content of chlorine and/or halogens in it. The low chlorine content of the third flash dross reduces the risk of entrainment of valuable metals in the gas leaving any stage of the pyrometallurgical process that produces off-gas, and therefore also reduces the risk of sticky solid deposits on coolers, filters and other items of equipment in equipment for off-gas treatment associated with such a step in the pyrometallurgical process.

In an embodiment of the process according to the present invention, the third pop-up dross is returned for processing to the process step prior to the first vacuum distillation step. This provides the advantage that valuable metals, in particular any trapped lead, can be easily recovered as part of one of the desired base products produced by the process of the present invention. Most of the lead captured in the third pop-up dross may preferably end up as part of the main product as soft lead, or if necessary, be returned to the third concentrated lead stream introduced as described elsewhere herein, and it can become part of the main product in the form of solid lead.

An advantage provided by this dross recycling capability is that it is possible to obtain an overall process that is much less complex, in particular compared to the very complex wet chemical recovery routes described in US 1,674,642.

The suitability of the third pop-up dross to be recycled to the pyrometallurgical process step allows more than one contaminant to be removed simultaneously in a single process/process step from the first concentrated lead stream, in this case As, Sb and Sn together. This is a significant improvement over the much more complex lead refining operations described in the art.

In an embodiment of the process according to the present invention, the first tin-rich product is subjected to a second distillation step in which the mainly lead and antimony are separated from the first tin-rich product by evaporation, whereby a second concentrated lead stream is obtained as a distillate product and second bottom product.

In an embodiment of the method according to the present invention, fresh lead containing feedstock is added to the feedstock fed to the second distillation step. The inventors have found that some lead is desirable in the feed to the second distillation stage, since more lead dilutes the vapor phase in the distillation stage. This has the advantage of facilitating the evaporation of antimony in the second distillation step, thereby improving the separation quality that can be achieved in the second distillation step. Lead dilutes the vapor phase in the distillation step and therefore serves as a kind of carrier for antimony. As a result, lead contributes to the removal of antimony from the main stream of tin, and therefore contributes to the final production of the main product in the form of high purity tin.

In an embodiment of the process according to the present invention, the second concentrated lead stream is subjected to a third distillation step, in which mainly lead and antimony are separated from the second concentrated lead stream by evaporation, whereby a third concentrated lead stream and a third bottom product are obtained as a distillate product. The authors found that the second concentrated stream of lead, as distillate from the second distillation step, is a more than suitable basis for obtaining the main product in the form of solid lead, since the tin that is carried away in this stream can be easily separated from most of the lead. and antimony through another distillation step. The purpose of the third distillation step may well be the selective evaporation of antimony and lead, if any, from the feedstock entering this step, with a third concentrated stream of lead being obtained as the distillate at this step.

In an embodiment of the method according to the present invention, fresh raw material containing lead is added to the raw material fed to the third distillation stage. The inventors have found that some lead is also desirable in the feedstock to the third distillation stage, since lead facilitates the evaporation of antimony. This has the advantage of facilitating the evaporation of antimony in the third distillation step, thereby improving the separation quality that can be achieved in the third distillation step. Lead dilutes the vapor phase in the distillation step and therefore serves as a kind of carrier for antimony. As a result, lead contributes to the recovery of most of the antimony contained in the third concentrated lead stream, and therefore contributes to the efficient production of the main solid lead product. The second concentrated lead stream may contain, for example, Pb/Sn/Sb concentrations of approximately 40/40/20 wt.% The authors found that this composition of the source material can be further improved. We prefer to dilute the feedstock for the third distillation step by adding fresh feedstock containing lead to about 10-12 wt% Sb and/or 18-10 wt% Sn. The authors found that this provides more headspace in the third distillation step, as well as lowering the melting point of the starting material. This allows the antimony Sb entering the third concentrated lead distillate stream to be better separated from the tin Sn which remains in the third underflow. An additional advantage is that if the third bottom product is returned for processing to a location upstream of the second distillation stage, a better separation in the third distillation stage ensures that the amount of antimony that circulates in the second and third distillation stages is reduced.

In an embodiment of the process according to the present invention, the third underproduct is at least partially and preferably completely recycled to the feed to the second distillation step and/or to the feed to the fractional crystallization step. The inventors have found that the third bottom product has a composition highly recyclable to at least one of these locations corresponding to the processes prior to the process of the present invention due to the high purity of the valuable metals and the low content of non-target metals. to extract, in the third bottom product. This provides the advantage that the valuable metals can be recovered in the form of the respective base products without great processing effort. We prefer to select a location in the process for returning the third bottom product for processing depending on the silver content of the stream, since the fractional crystallization step allows the recovery of silver and thereby preventing the accumulation of silver in the process to levels beyond acceptable levels.

In an embodiment, the method of the present invention further includes the step of removing at least one contaminant selected from metallic arsenic and tin from the third concentrated lead stream, whereby a purified solid lead stream is obtained as solid lead product. The inventors have found that the third concentrated lead stream can be further refined by means known in the art to obtain a purified solid lead stream as solid lead product.

In an embodiment of the method according to the present invention, this at least one contaminant is removed from the third concentrated lead stream by treating the third concentrated lead stream at a temperature of less than 600° C. with a second base and a second oxidizing agent, resulting in a fourth pop-up dross, containing the compound in the form of a metalate of the corresponding polluting metal, followed by the separation of the fourth pop-up dross from the stream of purified solid lead.

Third Concentrated Sweat+6

ok lead is preferably contacted with a combination of NaOH and NaNO ₃ . Chemical processes that are provided with these chemical reagents can be represented by the following reactions:

5 Pb + 6 NaOH + 4 NaNO ₃ → 5 Na ₂ PbO ₃ +2 N ₂ +3 H ₂ O (I) 5 Na ₂ PbO ₃ +4 As + 2 NaOH → 4 Na ₃ AsO ₄ +5 Pb + H ₂ O (II) Na ₂ PbO ₃ + Sn → Na ₂ SnO ₃ + Pb (III)

The key to these chemical processes is to enable the formation of an intermediate sodium plumbate (Na ₂ PbO ₃ ) via reaction (I). This intermediate plumbate is capable of reacting with As and/or Sn impurities in accordance with the corresponding reactions (II) - (III) and each time "captures" them in the corresponding compound in the form of sodium metallate, ensuring the release of Pb again in a free form. The compounds formed in the form of sodium metallates are sodium arsenate and sodium stannate, respectively.

The corresponding compounds in the form of sodium metallates accumulate in the floating phase, commonly referred to as "dross" or sometimes also "slag".

The fourth pop-up dross may be skimmed off the surface and may be subjected to further processing, preferably at a step in a preceding process, to recover at least some of its constituents.

In an embodiment of the method according to the present invention, the fourth pop-up dross contains at most 1.0 wt.% chlorine, preferably at most 1.0 wt.% halogens in total.

The authors found that the specified low content of chlorine and/or other halogens in the fourth pop-up dross makes the dross more suitable for input at the stage of the previous pyrometallurgical process, preferably at the stage of the process, at which at least one of the sodium metallates, which is a stannate (compound with Sn) and arsenate (compound with As) can be reduced to give the corresponding Sn or As metal, preferably also together with Pb, finally in its elemental form.

The fourth pop-up dross is more acceptable at the stage of the pyrometallurgical process due to the limited content of chlorine and/or halogens in it. The low chlorine content of dross reduces the risk of entrainment of valuable metals in the gas leaving any step of the pyrometallurgical process that produces off-gas, and therefore also reduces the risk of sticky solid deposits on coolers, filters and other items of equipment in waste treatment equipment. gases associated with such a stage of the pyrometallurgical process.

In an embodiment of the process according to the present invention, the fourth pop-up dross is returned for processing to the process step prior to the first vacuum distillation step. This provides the advantage that valuable metals, in particular any trapped lead, can be easily recovered as part of one of the desired base products produced by the process of the present invention. Most of the lead entrained in the fourth pop-up dross may preferably end up as part of the main product as soft lead or, if necessary, be returned to the third concentrated lead stream and become part of the main product as hard lead.

An advantage provided by this dross recycling capability is that it is possible to obtain an overall process that is much less complex, in particular compared to the very complex wet chemical recovery routes described in US 1,674,642.

The suitability of the fourth pop-up dross to be recycled back to the pyrometallurgical process step allows more than one contaminant to be removed simultaneously in a single process/process step from the first concentrated lead stream, in this case As and Sn together. This is a significant improvement over the much more complex lead refining operations described in the art.

In an embodiment of the method according to the present invention, the third concentrated stream of lead contains at least 0.50 wt.% and at most 15.0 wt.% antimony. The presence of antimony in a concentration in this range provides the advantage of improving the properties of the main solid lead product obtained from the third concentrated lead stream, taking into account end uses in which hard lead is preferred over soft lead.

In an embodiment of the process according to the present invention, the second bottom product is further refined to obtain the main product in the form of high purity tin. The inventors have found that the second bottom product is highly amenable to further refining to produce a high purity tin main product of very high economic value.

In an embodiment of the process according to the present invention, the second bottom product is treated with aluminum metal, preferably in excess against stoichiometry with respect to the amount of antimony present, the treatment being preferably accompanied by stirring and cooling the reaction mixture to a temperature below 400°C, followed by separation of the dross containing Al/Sb/As, which is formed during this processing. The authors found that aluminum easily forms solid intermetallic compounds with microimpurities contained in the tin stream, in particular, with antimony. The authors prefer to use an excess of aluminum against stoichiometry as this is more efficient in removing antimony, and any remaining aluminum can be removed quite easily, as further described herein. Mixing and cooling aid in the reaction and separation of the solid compounds formed from the molten tin. The inventors prefer cooling to approximately 250° C. as they have found that this provides a better balance between the rate of reaction enhanced by high temperatures and improved separation facilitated by lower temperatures. The generated dross containing Al/Sb/As can be removed and can be returned for processing to the stage of the previous pyrometallurgical process. The authors prefer to collect the dross containing Al/Sb/As in steel drums, which are closed and plugged to avoid contact of the dross with water, which can cause the formation of highly toxic gases - arsene and/or stibine. The aluminum is preferably added in the form of granules providing a high surface area and no dust problems. We prefer to add these pellets to the bath without vigorous agitation, preferably static to avoid the possibility of any wet pellet exploding due to sudden contact with hot liquid tin.

In an embodiment of the process according to the present invention, the second underproduct, after treatment with aluminium, and preferably also after removal of dross containing Al/Sb/As, is treated with a third base, preferably selected from NaOH, Ca(OH) ₂ and Na ₂ CO ₃ , and combinations thereof , more preferably NaOH, followed by the separation of the dross containing the base, which is formed during this treatment. The authors prefer to remove the Al/Sb/As dross before adding the third base in order to require less of this base. The authors prefer to use NaOH as the third base because this compound forms sodium aluminate-containing dross, which is more suitable for recycle to the upstream pyrometallurgical process. The authors prefer to perform this treatment several times in successive steps and based on the analysis of the tin flow to determine the content of aluminum in it to save chemicals. The envisaged chemical processes can generate hydrogen gas, so the inventors prefer to drop some sulfur granules onto the reaction liquid so that the sulfur will ignite at hot process temperatures and burn hydrogen that may be released during the reaction. The dross can be stiffened by adding silica, preferably in the form of sand.

In an embodiment of the process according to the present invention, the second underproduct, after treatment with a third base, is treated with sulfur, followed by separation of the S-containing dross that is formed by this treatment. Sulfur reacts with sodium and forms dross containing Na ₂ S. The authors prefer to increase the intensity of mixing at the end of this treatment to draw in more oxygen from the surrounding air, which oxidizes the sulfur remaining after the reaction, and the resulting sulfur oxides can easily escape from liquid end product.

In an embodiment of the method according to the present invention, at least part of the method is monitored and/or controlled by electronic means, preferably by means of a computer program. The inventors have found that electronically controlling the steps of the method according to the present invention, preferably by means of a computer program, provides the advantage of significantly better handling, with results that are significantly more predictable and closer to the process goals. For example, based on temperature measurements, optionally also pressure and/or level measurements, and/or combined with chemical analysis results of samples taken from the process streams and/or analysis results obtained online, the control program can control equipment related to the supply or removal of electricity, the supply of heat or coolant, regulation of flows and / or pressure. The authors have found that such monitoring or such control is particularly preferred/preferred for steps that are performed in a continuous mode, but they may also be preferred for steps that are performed in a batch or semi-continuous mode. In addition, the monitoring results obtained during or after the execution of the steps of the method according to the present invention are preferably also used to monitor and/or control other steps as part of the method according to the present invention and/or processes that are applied as antecedent or subsequent to the method. according to the present invention and as part of a general technological process, in which the technological process/method according to the present invention is only a part. Monitoring of the entire overall process is preferably carried out by electronic means, more preferably by at least one computer program. The overall process control is preferably carried out as far as possible by electronic means.

The authors prefer that computer control also ensures that data and commands are transmitted from one computer or one computer program to at least one other computer or one other computer program or module of the same computer program for monitoring and / or controlling other technological processes, including, but not limited to, the technological processes described in this document.

EXAMPLE

The following example shows in more detail how the method according to the present invention can be carried out and how the desired effect is achieved. The example also shows how the process according to the invention can be part of a larger overall process that produces more base products. The attached FIG. 1 shows a flow diagram of the method steps and the sequence that are performed in this example. The compositions given in this example are expressed in units of mass and are the result of analyzing samples taken daily and averaging the results over a working period of 73 days.

In figure 1, the reference positions denote the following elements of the claims:

one. Raw solder composition as raw material fed to pre-treatment step 100 2. NaOH added in pretreatment step 100 3. Sulfur added in pretreatment step 100 four. First pop-up dross generated in preprocessing step 100 5. Second pop-up dross generated in preprocessing step 100 6. Molten solder mixture obtained in pre-treatment step 100 7. First concentrated lead stream as distillate product from vacuum distillation step 200 eight. The first bottom product obtained from the first stage 200 of vacuum distillation 9. The first liquid product with an increased concentration of silver obtained on the side of the liquid fraction in the crystallization step 300 ten. The first product with an increased concentration of tin obtained in the crystallization step 300 eleven. Fresh starting material added in the second stage 400 vacuum distillation 12. Second concentrated lead stream as distillate product from second vacuum distillation step 400 13. The second bottom product from the second vacuum distillation step 400 fourteen. Aluminum granules added at stage 500 of tin refining fifteen. Third base added in tin refining step 500 16. Sulfur added in tin refining step 500 17. Dross containing Al/Sb/As and resulting from the tin refining step 500 eighteen. Dross containing a base and formed in the tin refining step 500 19. Dross containing sulfur and formed in the tin refining step 500 twenty. The main product in the form of high-purity tin, obtained from the tin refining step 500 21. The third concentrated stream of lead as a distillate product obtained in the third stage 600 vacuum distillation 22. The third bottom product obtained in the third stage 600 vacuum distillation 23. Copper added in the soft lead refining step 700 24. First base added in soft lead refining step 700 25. First oxidant added in the soft lead refining step 700 26. Third pop-up dross from soft lead refining step 700 27. Refined soft lead stream or product from soft lead refining step 700 28. Refined solid lead stream or product from solid lead refining step 800 29. Residues of distillate product 21 from previous production runs thirty. Second base added in solid lead refining step 800 31. The second oxidizer added in the solid lead refining step 800 32. Fourth pop-up dross from solid lead refining step 800 33. Fresh raw material added in step 100 raw solder pretreatment 34. Fresh starting material added in the third stage 600 vacuum distillation 35. Fresh starting material added in the fractional crystallization step 300 36. Fresh starting material added in the first stage 200 vacuum distillation 100 Pretreatment step 200 The first stage of vacuum distillation 300 Fractional crystallization stage 400 The second stage of vacuum distillation 500 Tin refining stage 600 The third stage of vacuum distillation 700 Soft lead refining stage 800 Solid Lead Refining Stage

To analyze the flow of molten metal, a sample of liquid metal is taken, poured into a mold and allowed to cool to a solid state. One surface of a solid sample is prepared by passing the sample one or preferably several times through a Herzog HAF/2 milling machine until a clean and flat surface is obtained. After that, a clean and flat surface of the sample is analyzed using the Spectrolab M spark optical emission spectroscopy (OES) device from Spectro Analytical Instruments (USA), also available from Ametek (Germany), while the parameters, crystals, detectors and tube can be be easily selected and adapted to obtain the most appropriate performance for a given accuracy and/or limit of detection/threshold. The analysis provides results for various metals in the sample, including copper, bismuth, lead, tin, antimony, silver, iron, zinc, indium, arsenic, nickel, cadmium and even elemental sulphur, and this is true for most of these metals up to the detection limit, constituting approximately 1 ppm. by weight.

For dross analysis, the inventors prefer to use an X-ray luminescence (XRF) method with proper calibration, preferably using a PANalytical Axios XRF spectrometer from PANalytical B.V. (Netherlands). This method is also preferred to optical emission spectroscopy (OES) mentioned above for the analysis of metal samples containing significant amounts of contaminants, such as stream 6 and the streams preceding it in the sequence diagram in the attached Fig.1. In addition, by this method, the characteristics can be easily selected and adapted to optimize the results in terms of accuracy and/or detection limit most suitable for the purpose of the analysis.

Raw solder raw material 1 was obtained by refining materials containing copper, lead and tin in a copper smelter (not shown), which produces an intermediate product in the form of "black copper" containing approximately 85 wt.% Cu. This black copper was then subjected in a copper refinery to a series of pyrometallurgical refining steps (not shown) which produced, on the one hand, a higher purity copper main product and, on the other hand, a number of slag by-products. As part of the refining operations, raw solder feedstock 1 is recovered from some of these refining slags. Purification of this raw solder is performed through a series of pre-treatment steps 100 to remove a significant amount of metallic impurities contained, the presence of which would otherwise create a risk of problems in subsequent vacuum distillation steps. The impurities that are set to be removed in the cleaning steps are mainly Cu, Fe, Ni and/or Zn, and the goal of cleaning the raw solder to acceptable levels is to allow further smooth and trouble-free processing of the solder through the use of vacuum distillation.

Raw solder 1 could be obtained from previous refining operations at a temperature of approximately 835°C. In the first step of a series of 100 cleaning operations, the solder was cooled to 334° C., and this was done in two steps. In the first cooling step, the raw solder was cooled to approximately 500° C. and the first dross was removed from the surface of the molten liquid metal. In the second cooling step, the raw solder was further cooled to 334°C and the second dross was removed from the surface of the molten liquid metal. During the cooling step, a bulk dross was formed which contained most of the copper present in the raw solder and which was removed as a by-product (not shown) and returned for processing to one of the stages of the preceding pyrometallurgical process. The overall flow rate and concentrations of metals of interest in the remaining solder intermediate (stream 1) are shown in Table 1. The copper content of the solder was reduced to an average of 3.0000 wt% by this sequence of cooling and dross removal steps. The concentrations of Fe and Zn in the solder were also significantly reduced. All phases representing the dross formed during the cooling operation were removed (not shown) and returned for processing to the previous process carried out in the smelter, so that the value of the valuable metals contained in the dross can be increased to the maximum possible degree.

Table 1. Raw solder after the cooling step wt% Unrefined solder
one tons/day 98.4 Bi 0.0163 Cu 3.0000 Fe 0.0007 Ni 0.0015 Pb 69.5000 Sb 0.8305 sn 26.7414 Zn 0.0028 Ag 0.0290 Au 0.0010 As 0.0515 CD 0.0010 In 0.0125 S 0.0025 Te 0.0007 Total 100.1914

In the second part of the 100 purification sequence, solid sodium hydroxide (stream 2) was added to the solder intermediate according to Table 1. This processing step allowed the zinc to bind with sodium hydroxide presumably to form Na ₂ ZnO ₂ and form a separate phase which separated as the first floating hard dross from the solder and which was removed as stream 4. As a result, the zinc content in the solder stream 6 was further reduced. The amount of sodium hydroxide was adjusted so that the Zn concentration in the solder was reduced to 13 ppm. by weight (Table 2). The dross that was formed at this stage was also returned for processing (stream 4) to the previous stage at the smelter, where zinc can be sublimated and recovered as powdered zinc oxide.

In the next part of the sequence of 100 purification operations, after adding sodium hydroxide and removing the phase of the first floating solid dross 4, some elemental sulfur was also added (stream 3), which is approximately 130%, taking into account the stoichiometry in relation to the amount of copper present in the metal phase, for further reduction of the copper content in the solder. Elemental sulfur was used in the form of sulfur pellets available from Zaklady Chemiczne Siarkopol, Tarnobrzeg (Poland). Sulfur 3 reacted primarily with copper to form copper sulfides which migrated to the second floating dross. This second pop-up dross was then removed/skimmed off as stream 5 and recycled to the appropriate step in the upstream process. Following the addition of sulfur in step 100, additional sodium hydroxide (stream 2) was added to chemically bind any remaining trace sulfur to form another dross. After allowing the reaction to proceed for some time, a small amount of granulated sulfur 3 was scattered/spread over the surface of the bath. The sulfur ignited and provided for the combustion of any hydrogen that might have escaped from the liquid as a by-product of the reaction. Thereafter, a small amount of white sand was scattered/spread over the dross drying/hardening bath before it was removed from the process (stream not shown) and returned to the upstream process for processing. The purified solder thus obtained (stream 6, the speed and composition of which are given in Table 2) contained only 38 ppm. Cu and was further processed as the molten solder mixture obtained in pretreatment step 100 by vacuum distillation in step 200. The second pop-up dross 5 was processed in a previous refining process so that its content of valuable metals could be increased.

Table 2. Purified solder for vacuum distillation wt% Molten solder
mixture - 6 tons/day 72.0 Bi 0.0326 Cu 0.0038 Fe 0.0004 Ni 0.0009 Pb 73.1206 Sb 0.8012 sn 25.8694 Zn 0.0013 Ag 0.0500 As 0.0871 Au 0.0015 CD 0.0020 In 0.0202 S 0.0053 Te 0.0010 Total 99.9973

The molten solder mixture 6 was further processed by using vacuum distillation (step 200) at an average temperature of 982° C. and an average absolute pressure of 0.012 mbar (1.2 Pa). The vacuum distillation step resulted in two product streams. On the one hand, a first concentrated lead stream was obtained as distillate product stream 7, which contained mainly lead, and, on the other hand, a product stream was obtained as first underproduct 8 of the first distillation stage 200, which contained mainly tin. The flow rates and data compositions of the two distillation product streams 7 and 8 are shown in Table 3.

Table 3. Product streams resulting from the first
vacuum distillation 200 wt% Distillate 7 Lower
eight tons/day 61.8 24.8 Bi 0.0425 0.0014 Cu 0.0000 0.0122 Fe 0.0000 0.0015 Ni 0.0000 0.0028 Pb 99.5375 1.0055 Sb 0.2233 1.9800 sn 0.1006 96.3129 Zn 0.0018 0.0001 Ag 0.0031 0.1400 As 0.0746 0.0700 Au 0.0000 0.0043 CD 0.0024 0.0000 In 0.0057 0.0460 S 0.0071 0.0000 Te 0.0014 0.0000 Total 100.0000 99.5767

The first vacuum distillation step 200 was performed continuously and was able to run this step for a period of approximately three (3) years without any blockage or fouling of the distillation equipment caused by the formation of intermetallic compounds.

The first concentrated stream 7 of lead was obtained from the distillation equipment at a temperature of approximately 562°C. The temperature of the stream 7 was adjusted to be approximately 450° C. with agitation before subjecting the stream to further refining. Provided the possibility of accumulation of successive volumes corresponding to 100-120 tons of flow 7 in the tank. These volumes were subjected to the soft lead refining operation 700 in batches. A sample was taken from each batch and analyzed for As, Sn and Sb content to determine the amounts of solid sodium hydroxide (stream 24) and solid sodium nitrate (stream 25) required to react with the As, Sn and Sb present in the metal phase , and these amounts were added as the first base and the first oxidizing agent. Sampling and analysis were repeated after allowing the reaction to proceed for some time and after removing the third pop-up dross 26 resulting from the reaction. If the result was unsatisfactory, this process step was repeated. For the total volume of soft lead that was produced over a working period of 73 days, 29.3 metric tons of sodium hydroxide (401 kg per day) and 15.5 metric tons of sodium nitrate (212 kg per day) were used in the process to remove more parts of an average of 46 kg of As per day, 62 kg of Sn per day and 138 kg of Sb per day, with an average of 246 kg of these 3 elements removed per day, which were present in the source material fed to stage 700 as stream 7 For each batch, a third flash dross phase was formed at this refining step, which contained most of the As, Sn and Sb present in the first concentrated lead stream 7 and was removed as a by-product (stream 26). A sample was taken from the third dross phase and analyzed to determine the chlorine content using the method according to DIN EN 14582. The analysis showed the presence of chlorine in an amount of approximately 129 ppm. by weight. The soft lead base product 27 was then poured into molds and allowed to solidify and cool to form lead ingots.

For most portions, a small amount of copper 23 was added to the starting material for step 700 to produce some soft lead containing Cu. The small amount of copper present improves the mechanical properties of the soft lead, making the soft lead more suitable for rolling into a thin layer/film of lead for the construction industry or for surface coating with lead. A number of batches that had above average Bi content were also separated as soft lead with increased Bi concentration, acceptable in certain end uses and providing the advantage that Bi containing feedstocks become more acceptable to the process of the present invention. and/or for upstream processes providing raw materials for the process. This refining of soft lead was performed intermittently/in batches in the same equipment as the equipment in which refining of hard lead is performed, which is discussed further below. As a result of the transition between portions of soft lead and hard lead, some material with an intermediate quality is formed, which is sold on the market as "unrefined soft lead". The average daily outputs (during the 73 day production period under consideration) and the data compositions of the various streams of the 27 soft lead products are shown in Table 4.

Table 4. Composition of end products 27 as soft lead
(% mass) soft lead products
27 Unrefined soft lead Soft lead containing Cu Soft lead with increased Bi concentration tons/day 5.7 39.8 14.8 Bi 0.0905 0.0319 0.0568 Cu 0.0001 0.0428 0.0008 Fe 0.0000 0.0000 0.0000 Ni 0.0000 0.0000 0.0000 Pb 99.6306 99.9026 99.9240 Sb 0.2279 0.0000 0.0000 sn 0.0208 0.0006 0.0004 Zn 0.0001 0.0001 0.0001 Ag 0.0032 0.0034 0.0025 As 0.0259 0.0002 0.0002 CD 0.0002 0.0000 0.0000 In 0.0007 0.0001 0.0001 S 0.0006 0.0003 0.0003 Te 0.0000 0.0000 0.0000 Au 0.0000 0.0000 0.0000 Total 99.7727 99.9820 99.9852

The first bottom product 8 from the first vacuum distillation step 200 was mixed with the third bottom product 22 from the subsequent third vacuum distillation step 600, and the mixture was fed into the fourth zone of the first crystallizer having 12 temperature zones. The crystallizer was a cylindrical tank, slightly inclined from a fully horizontal position, and contained an internal rotating screw to move the resulting crystals from the lower end to the upper end of the cylindrical tank. The temperature zones were numbered from 0 to 11 from the bottom end to the top end. Using appropriate heating and cooling means, a temperature profile was created within the mold. The temperature of zone 3 into which the feed material entered was adjusted to be approximately 210°C. The temperature was increased stepwise from zone 3 to zone 11 (230-250°C), located at the top of the mold, from which crystals with a high concentration of tin were removed from the device. The temperature was reduced slightly in the mold downward from zone 3 to zone 0 (199°C), but increased again in zone 0 to approximately 220°C to ensure that the temperature in this zone would always remain above the liquidus line on the phase diagram. , so that any build-up of solids on the auger blades was avoided, which could otherwise lead to the need for operator intervention and temporary decommissioning of the equipment.

Before entering the feed stream into the crystallizer, the stream was passed through a buffer tank capable of holding the volume of product produced over several hours, with some agitation in this tank ensuring that any temperature changes that may have occurred in the preceding steps are smoothed out so that the temperature of the feed material , entering the zone 3 of the mold, is fairly constant, and any changes in it are very slow. In addition, the temperature of the feedstock entering zone 3 is kept slightly higher than the temperature in zone 3 of the mold to prevent the formation of solids in the supply system. Upon entering zone 3 of the mold, the feed stream is cooled and its temperature is within the range in which the stream having a given composition separates into a solid phase consisting of small crystals that have an increased tin content and is in equilibrium with the liquid a phase that has a lower content of tin, but a higher content of lead and precious metals. Increasing the temperature of the liquid moving downward in the mold from zone 1 further down to zone 0 provided the advantage that build-up of solids was prevented at the periphery of the screw blades at the bottom of the cylindrical vessel, so that there was sufficient space under the screw blades for allowing liquid to flow from the upper end of the cylindrical reservoir to the lower end.

The mold was tilted so that the liquid phase in the reservoir could easily move by gravity from the higher end to the lower end of the device. A rotating screw inside the mold allowed the crystals to move in the opposite direction through the continuous liquid phase present in the mold. The liquid level in the crystallizer was kept below the crystal "overflow" to minimize liquid entrainment along with the first product with increased tin concentration, but high enough to facilitate heat transfer from the vessel wall to the contents of the vessel. The crystals ending at the higher end had an increased concentration of tin, and substantially all of the lead and precious metals from the feed material were recovered as a liquid first effluent exiting the mold at the lower end. In addition, this first withdrawn product contained tin in a significant amount, but at a concentration below the level of the tin concentration in the raw material fed to the mold.

The Sn crystals were removed from the upper end of the first mold and were introduced into the fourth zone (zone 3 again) of the second mold, also having 12 temperature zones, numbered 0 to 11. The second mold also used a temperature profile similar to the temperature profile in the first mold, which caused additional separation of the second liquid effluent from the first crystals with an increased concentration of tin before these crystals exit the second crystallizer at the upper end (stream 10).

Antimony, which enters the mold along with the initial material, basically repeats the path of the main flow of tin. The product withdrawn from the second mold was returned to the first mold where it was mixed with the starting material. When the Pb concentration was considered to be excessive, the product withdrawn from the second crystallizer was temporarily returned to the feed fed to the preceding first vacuum distillation step 200 to maintain a higher Ag concentration factor from the vacuum distillation underflow stream 8 to the resulting first liquid effluent 9 with an increased concentration of silver. In addition, when the concentration of Cu is increased in the streams produced in the crystallizers, and therefore also in the product withdrawn from the second crystallizer, this withdrawn product is at least temporarily preferably returned for processing to a process step earlier than the supply of the starting material. to the first mould, preferably returned to the raw material supplied to the first stage of the cleaning sequence 100 for mixing with the raw solder composition 1.

The first liquid effluent with elevated silver concentration exited the first mold as a by-product, which is an alloy of Sn and Pb and contains most of the Ag present in the feed to the mold. The flow rates and compositions of product streams 9 and 10 exiting the 2-mold set at step 300 are shown in Table 5. Sb was also found to have an increased concentration in the first tin-enhanced crystal phase emerging from the second mold. , but some Sb was also recovered in the first liquid effluent with increased silver concentration. Table 5 shows the resulting/net discharge volume of the liquid discharge product 9 with increased concentration of silver and its composition. The return of the liquid withdrawn product with a high concentration of silver from the lower end of the first mold to the source material fed to the first mold was carried out temporarily and depending on its composition to further increase the concentration factor of Ag from the source material fed to the molds (streams 8 + 22), to the resulting first liquid effluent 9 with an increased concentration of silver.

Table 5. Product streams obtained in a set of crystallizers wt% First liquid product with higher concentration of silver
9 The first product with a higher concentration of tin
ten tons/day 1.3 27.0 Bi 0.0079 0.0010 Cu 0.2900 0.0014 Fe 0.0012 0.0016 Ni 0.0215 0.0023 Pb 16.5000 0.2387 Sb 0.4020 2.1000 sn 79.5000 97.0536 Zn 0.0042 0.0000 Ag 2.8000 0.0100 As 0.1144 0.0680 CD 0.0001 0.0000 In 0.1039 0.0411 S 0.0000 0.0000 Te 0.0000 0.0000 Au 0.0129 0.0034 Total 99.7581 99.5211

The resulting first silver concentrated liquid effluent 9 was transferred from the first crystallizer to a subsequent purification step (not shown) to recover all precious metals as well as Sn and Pb. For this purpose, the liquid effluent product with a high concentration of silver was cast as anodes and subjected to an electrolysis step, in which cathodes containing pure Pb and Sn were obtained, and the remaining metals remained in the anode sludge. Typical conditions for this stage of electrolysis: electrolyte based on hexafluorosilicic acid (H ₂ SiF ₆ ), fluoroboric acid and/or phenylsulfonic acid; temperature - approximately 40°C; current density - 140-200 A / m ² ; the distance between the electrodes is approximately 100 mm. Antimony can be added to the composition of the anodes, typically up to a concentration of about 1.5 wt.% This provides the advantage that the anode sludge remains attached to the anodes and is not dispersed in the electrolyte. To prevent the formation of a coating film on the entire surface of the anodes, which leads to inhibition of electrolysis, a part of the anodes can be periodically and sequentially removed from the bath, the anode sludge on them can be removed, for example, mechanically, and then the cleaned anodes can be placed back in electrolyzer. The anodes can also be designed such that the cleaned anodes are thin enough that it is more economical and/or efficient to melt them down to make new anodes. This anode sludge (averaging about 180 kg per day) was separated, for example, by filtration from entrained/entrained electrolyte, and this anode sludge contained about 20 wt.% silver, as well as gold with a significantly lower concentration, along with most of the remaining metals, present in the first liquid effluent with a high concentration of silver, including antimony and any platinum group metals (PGMs). Anode sludge was subjected to additional processing to extract silver and other precious metals. The filtrate was returned to the cell.

The first tin-rich crystals 10 obtained in the second crystallizer were further processed by a second vacuum distillation step 400 performed at an average temperature of 1049° C. and an average absolute pressure of 0.005 mbar (0.5 Pa). Over a working period of 73 days, raw material 11 containing lead, in an amount of 157.6 tons, averaging approximately 2.2 metric tons per day, was added gradually to the first crystals with an increased concentration of tin to maintain a low solidification temperature of the distillate product obtained at step 400. The flow rate and composition of stream 11 are shown in Table 6.

Table 6. Added raw materials in the starting material for the second vacuum distillation wt% Raw materials containing Pb
eleven tons/day 2.2 Bi 0.0299 Cu 0.0161 Fe 0.0018 Ni 0.0003 Pb 58.8711 Sb 0.0006 sn 41.0558 Zn 0.0001 Ag 0.0036 As 0.0015 CD 0.0000 In 0.0017 S 0.0002 Te 0.0000 Au 0.0001 Total 99.9827

The second vacuum distillation step 400 produced two product streams. On the one hand, a product stream 12 was obtained as the distillate product, which contained mainly most of the lead, antimony and silver from the feed plus some tin, and, on the other hand, a product stream was obtained as the second underproduct 13, which contained mainly tin with only trace amounts of other components. The flow rates and compositions of these two distillation product streams 12 and 13 are shown in Table 7.

Table 7. Product streams resulting from the second
vacuum distillation wt% Distillate 12 Lower
13 tons/day 3.6 25.6 Bi 0.0189 0.0004 Cu 0.0000 0.0028 Fe 0.0000 0.0019 Ni 0.0000 0.0025 Pb 37.8602 0.0011 Sb 13.0000 0.3800 sn 47.7097 99.4584 Zn 0.0000 0.0000 Ag 0.0560 0.0029 As 0.3900 0.0178 Au 0.0000 0.0036 CD 0.0000 0.0000 In 0.3050 0.0006 S 0.0001 0.0000 Te 0.0000 0.0000 Total 99.3400 99.8719

The second vacuum distillation step 400 was performed continuously and was able to run this step for a period of approximately three (3) years without any blockage or fouling of the distillation equipment caused by the formation of intermetallic compounds.

The second bottom product 13 from step 400 was further refined in batches in three successive steps and shown collectively in the flowchart as tin refining step 500. The first tin refining step consisted of cooling the second bottom product 13 and adding some aluminum granules (stream 14) to the second bottom product, which had an average temperature of 430° C., with stirring to react with Sb and As and remove Sb and As to the level concentration, corresponding to the established international industrial standards. The amount of Al to be added was determined based on the analysis of the second underflow 13, and included an additional amount subject to the requirement of a ratio higher than stoichiometric. The composition was analyzed again after the reaction, and if the result was insufficient, in particular with regard to the Sb content, additional Al was added to initiate the second reaction step. In general, aluminum was used in an average amount of about 4.3 kg of Al per metric ton of second bottom product 13. Approximately 30 minutes after the last addition, heating and stirring was stopped and the liquid molten metal composition was allowed to cool. During this cooling to a temperature averaging about 250°C, a layer of dross containing Al/Sb/As was formed, and this dross was periodically removed from the surface of the molten liquid metal. The dross was harvested and stored in dry, closed and double-walled steel drums to prevent contact with water or moisture which could lead to the formation of stibine and/or arsine. The barrels were removed as a by-product (stream 17) and returned for processing to a step in the prior pyrometallurgical process where they were introduced unopened into the liquid bath of molten metal and/or slag, thus avoiding any risk of contact with moisture.

After raising the temperature of the tin product back to about 330° C., the molten liquid metal was subjected to a second tin refining step in which solid sodium hydroxide (stream 15) was added as the third base. In this processing step, aluminum binding was carried out with sodium hydroxide, presumably to form Na ₃ AlO ₃ , and a separate phase was formed, which separated as a floating solid dross from the molten liquid metal, and which was removed as stream 18. After allowing the reaction to proceed in for some time, a small amount of granular sulfur was scattered/spread over the surface of the bath. The sulfur ignited and provided for the combustion of any hydrogen that might have evolved from the molten liquid metal as a by-product of the reaction. As a result, the aluminum content of the second bottom product 13 was further reduced. The amount of sodium hydroxide to be added was adjusted so that the concentration of aluminum in the second bottom product was reduced to values below the detection limit of 1 ppm. by weight (Table 8). Dross, which was formed at this stage, was also returned for processing (stream 18) to the stage of the previous pyrometallurgical process.

In the third and final tin refining step, some elemental sulfur (stream 16) was added to further reduce the copper content of the molten liquid metal and to remove any sodium hydroxide that remained from the second tin refining step. Sulfur in granular form was used as elemental sulfur, which can be obtained from Zaklady Chemiczne Siarkopol, Tarnobrzeg (Poland). Sulfur 16 reacted primarily with copper to form copper sulfides and with sodium hydroxide to form Na ₂ SO ₂ , which moved into another pop-up dross phase. Following the addition of sulfur, the stirrer was operated for approximately 10 minutes to oxidize any remaining trace sulfur and form more dross. Dross was removed from the molten liquid metal as stream 19. The high purity Sn main product thus obtained (stream 20, whose rate and composition are shown in Table 8) contained only 14 ppm. Cu, and it was cast into ingots weighing 22 kg, the ingots were stacked, weighed and tied. Dross 19, containing sulfur, was subjected to processing at the stage of the previous pyrometallurgical process.

Table 8. End product as high purity Sn wt% High purity Sn
twenty tons/day 24.6 Bi 0.0001 Cu 0.0014 Fe 0.0004 Ni 0.0000 Pb 0.0008 Sb 0.0160 sn 99.9758 Zn 0.0000 Ag 0.0030 As 0.0006 Au 0.0001 CD 0.0000 In 0.0006 S 0.0000 Te 0.0000 Al 0.0001 Total 99.9989

The distillate product 12 obtained in the second vacuum distillation step 400 was further processed in the third vacuum distillation step 600, performed at an average temperature of 1000° C. and an average absolute pressure of 0.033 mbar (3.3 Pa). In the third stage 600 vacuum distillation received two streams of products. On the one hand, a product stream 21 was obtained as a distillate product, which contained mainly lead and antimony, and, on the other hand, a product stream was obtained as a third bottom product 22, which contained mainly tin and part of antimony, and also most noble metals present in the starting material for distillation. The flow rates and compositions of these two distillation product streams 21 and 22 are shown in Table 9.

Table 9. Product streams resulting from the third vacuum distillation wt% Distillate 21 Lower
22 tons/day 5.5 2.5 Bi 0.0474 0.0011 Cu 0.0000 0.0265 Fe 0.0000 0.0004 Ni 0.0000 0.0075 Pb 90.1133 0.7827 Sb 9.1014 2.1363 sn 0.5379 96.8647 Zn 0.0002 0.0001 Ag 0.0100 0.0950 As 0.4700 0.0730 CD 0.0019 0.0000 In 0.1860 0.0297 S 0.0022 0.0000 Te 0.0013 0.0000 Au 0.0000 0.0000 Total 100.4716 100.0170

The third vacuum distillation step 600 was performed continuously and was able to run this step for a period of approximately three (3) years without any blockage or fouling of the distillation equipment caused by the formation of intermetallic compounds.

The third bottom product 22 was returned for processing to the first mold used in the previous step 300, in which it was mixed with the first bottom product 8 obtained in step 200 to recover the valuable metals contained therein.

The distillate product 21 was further refined in step 800 in batches in the same equipment used during the soft lead refining step 700 that was performed on the first concentrated lead stream as distillate product stream 7 from the first vacuum distillation step 200. In addition, during a working period of 73 days, an additional 810.2 metric tons of distillate product obtained from the third stage of vacuum distillation, which remained from previous production runs (stream 29), averaging approximately 11.1 tons per day, was mixed with stream 21 and refined with it. The refining of this solid lead was performed in batches with a total feed volume of 100-120 tons. During the 73 days corresponding to the operating time considered in this example, approximately 9 days were spent refining 1159 tons of hard lead at approximately 129 tons per day, and for 43 days the equipment was used to refine a total of 4400 tons of soft lead products. , as described above, at an average of approximately 102 tons per day.

The molten liquid metal feedstock supplied to the solid lead refining step 800 was first heated to approximately 450° C. while stirring. A sample was taken and analyzed for As and Sn content to determine the amounts of solid sodium hydroxide (stream 30) and solid sodium nitrate (stream 31) considered necessary to remove As and Sn from the molten metal phase, and these amounts were added as a second base and a second oxidizing agent. Over the 73 day work period considered for this example, a total of 15.2 metric tons of sodium hydroxide (average 208 kg per day) and 7.6 metric tons of sodium nitrate (average 104 kg per day) were added at this a refining step to remove most of the averaging 26 kg As per day and 32 kg Sn per day that entered stage 800 along with streams 21 and 29. Nearly all of the antimony from the 1502 kg Sb per day present in the feed streams fed to the solid lead refining step 800, remained in the product 28 as refined solid lead. This solid lead refining step produced a total fourth flash dross phase that contained most of the As and Sn present in distillate products 21 and 29 and was removed as a by-product (stream 32). A sample was taken from the fourth dross phase and analyzed to determine the chlorine content using the method according to DIN EN 14582. The analysis showed the presence of chlorine in an amount of approximately 130 ppm. by weight. The flow rate and composition of the final product stream 28 in the form of purified solid lead are shown in Table 10.

Table 10. Composition of the final product in the form of solid lead wt% solid lead
28 tons/day 15.9 Bi 0.0550 Cu 0.0000 Fe 0.0000 Ni 0.0000 Pb 91.4680 Sb 8.9900 sn 0.0192 Zn 0.0001 Ag 0.0112 As 0.0025 CD 0.0002 In 0.0005 S 0.0005 Te 0.0000 Au 0.0000 Total 100.5472

Thus, the goal of this solid lead refining step in step 800 was only to remove only an average of 58 kg of impurities per day, which is significantly less than the amount to be removed in step 700. In addition, the concentrations of As and Sn in the feed material fed to step 800 were also higher than their concentrations in the feed material fed to step 700. Therefore, the goals of step 800 are achieved much more easily than the goals of step 700. With respect to the total amount of (As+Sn+Sb) that is fed to corresponding lead refining steps 700 and 800, step 800 consumes significantly less chemicals and generates significantly less pop-up dross than step 700, which also has the advantage that there is less cost associated with returning the pop-up dross for processing in the previous pyrometallurgical technological process. It was also found from observations that at step 800 As and Sn could be successfully removed to very low levels, with almost no removal of any antimony Sb required.

From the full description of the present invention, those skilled in the art will appreciate that the invention may be practiced over a wide range of parameters within what has been claimed without departing from the scope of the invention as defined by the claims.

Claims (63)

1. Method for separating by fractional crystallization (300) the molten mixture (8) of crude tin containing lead and silver into the first liquid discharge product (9) enriched in silver on the side of the liquid fraction obtained in the crystallization stage, and the first product (10) , enriched in tin, on the side of the crystalline fraction obtained in the crystallization stage, while the first liquid discharge product (9), enriched in silver, consists, on a dry weight basis, of: at least 6.0 wt.% and at most 27.5 wt.% lead; at least 72.5 wt.% and at most 91 wt.% tin; at least 95.0 wt.% and at most 99.0 wt.% lead and tin together; at least 0.75 wt.% and at most 4.50 wt.% silver; and at least 0.24 wt.% antimony, and additionally also contains in terms of dry weight: at least 0.05 wt.% and at most 0.5 wt.% arsenic; at least 0.05 wt.% and at most 0.6 wt.% copper; at least 0.0030 wt.% and at most 0.0500 wt.% nickel; at least 0.0010 wt.% and at most 0.40 wt.% bismuth; at most 1.0 wt% iron or at least 0.0005 wt% and preferably at most 0.0500% gold, while the rest are impurities. 2. The method according to claim 1, wherein the crude tin mixture (8) contains at least 0.1% by weight and at most 7.0% by weight of lead. 3. Process according to claim 1 or 2, wherein the crude tin mixture (8) contains at most 6.5% by weight of Pb. 4. The method according to any one of paragraphs. 1-3, in which the concentration of lead in the mixture (8) of crude tin is at least 3.0 times the concentration of silver in mixture (8) of crude tin. 5. The method according to any one of paragraphs. 1-4, in which the mixture (8) of crude tin contains at least 10 ppm. silver (Ag) by weight and optionally at most 0.85 wt.% silver. 6. The method according to any one of paragraphs. 1-5, wherein the black tin mixture (8) contains at least 0.1% by weight of antimony (Sb). 7. The method according to any one of paragraphs. 1-6, in which the first product (10), enriched in tin, contains at least 0.05 wt.% lead. 8. The method according to any one of paragraphs. 1-7, in which the first product (10), enriched in tin, is obtained continuously. 9. The method according to any one of paragraphs. 1-8, wherein the entire fractional crystallization step (300) is performed continuously. 10. The method according to any one of paragraphs. 1-9, wherein the first silver-enriched liquid effluent (9) is returned partially and/or temporarily to the feedstock fed to the fractional crystallization step (300). 11. The method according to any one of paragraphs. 1-10, wherein the fractional crystallization step (300) includes at least 4 crystallizer stages. 12. The method according to any one of paragraphs. 1-11, wherein the crystallizer used in the fractional crystallization step (300) comprises a feed stage for receiving raw material fed into the crystallizer, wherein the crystallizer further comprises at least one crystallizer stage and preferably at least 2 stages between the feed stage and each of the elements of the mold, designed to release the product. 13. The method according to any one of paragraphs. 1-12, in which the temperature profile at all stages in the stage (300) fractional crystallization set in the range of 180-270°C. 14. The method according to any one of paragraphs. 1-13, in which the temperature difference between two adjacent stages in the fractional crystallization stage (300) excluding the feeding stage and the final stage is set to at most 20°C. 15. The method according to any one of paragraphs. 1-14, in which the fractional crystallization step (300) is performed in at least 2 crystallizers in series, wherein the product coming from the crystal fraction zone in the previous crystallizer is fed into the subsequent crystallizer, while it is either completely fed into the supply stage in the subsequent crystallizer, or only its first part is fed into the feed stages in the subsequent mold and its second part is fed into the second stage of the subsequent mold, different from the feed stage, this second stage being selected from the stages located between the feed stage and the final stage on the side of the crystalline fraction in the subsequent mold, this second stage being preferably separated from the supply stage by at least one and preferably two or three intermediate stages. 16. The method according to claim 15, in which the product obtained on the side of the liquid fraction in the subsequent crystallizer is at least partially and preferably completely at least temporarily returned to the previous crystallizer, if necessary in the supply stage, but preferably in the second stage, which selected from stages located between the feed stage and the final stage on the side of the crystalline fraction in the previous crystallizer, while this second stage is preferably separated from the final stage by at least one and preferably two or three intermediate stages. 17. The method according to any one of paragraphs. 1-16, in which the mixture (8) of crude tin additionally contains at least 1 ppm. by weight of at least one metal selected from copper, iron, bismuth, nickel, zinc, gold, indium and arsenic. 18. The method according to any one of paragraphs. 1-17, in which the black tin mixture (8) contains at least 99.0 wt.% tin, lead, antimony and silver together. 19. The method according to any one of paragraphs. 1-18, wherein the first silver-enriched liquid effluent (9) is subjected to a fourth distillation step in which lead is removed by evaporation and enters a fourth concentrated lead stream obtained as a distillate product, whereby a fourth underproduct is obtained distillation. 20. The process of claim 19, wherein the fourth bottom distillation product is subjected to a fractional crystallization step that produces a second silver-rich effluent on the liquid side and a second tin-rich product on the crystalline side. 21. The method according to any one of paragraphs. 1-20, wherein the first tin-rich product (10) is subjected to a second distillation step (400) in which lead and antimony are mainly separated from the first tin-rich product (10) by evaporating them, whereby a as a distillate product, a second concentrated lead stream (12) and a second bottom product (13). 22. The process according to claim 21, wherein fresh lead containing feedstock (11) is further fed to the second distillation step (400) and added to the first tin-rich product (10). 23. The process according to claim 21 or 22, wherein the second concentrated lead stream (12) is subjected to a third distillation step (600) in which lead and antimony are mainly separated from the second concentrated lead stream (12) by evaporating them, whereby a third concentrated lead stream (21) and a third bottom product (22) are obtained as distillate product. 24. The process of claim 23, wherein fresh lead containing feedstock (34) is further fed to the third distillation step (600) and added to the second concentrated lead stream (12). 25. The process according to claim 23 or 24, wherein the third underproduct (22) is at least partially and preferably completely recycled to the feed to the second distillation step (400) and/or to the feed to step ( 300) fractional crystallization. 26. The method according to any one of paragraphs. 23-25 further comprising the step (800) of removing at least one impurity selected from metallic arsenic and tin from the third concentrated lead stream (21), whereby a purified solid lead stream is obtained as product (28) as solid lead . 27. The method according to p. 26, in which this at least one impurity is removed by processing the third concentrated stream (21) of lead at a temperature of less than 600 ° C, using the second base (30) and the second oxidizing agent (31), in as a result, a fourth pop-up dross (32) is formed containing the compound in the form of a metalate of the corresponding polluting metal, after which the fourth pop-up dross (32) is separated from the stream (28) of purified solid lead. 28. The process according to claim 27, wherein the fourth pop-up dross (32) contains at most 1.0% by weight of chlorine, preferably at most 1.0% by weight of halogens in total. 29. The method according to claim 27 or 28, wherein the fourth pop-up dross (32) is returned for processing to the process step preceding the first vacuum distillation step (200). 30. The method according to any one of paragraphs. 23-29, in which the third concentrated stream (21) of lead contains at least 0.50 wt.% and at most 15.0 wt.% antimony. 31. The method according to any one of paragraphs. 21-30, in which the second bottom product (13) is further refined to obtain the main product (20) in the form of high purity tin. 32. Process according to claim 31, wherein the second bottom product (13) is treated with aluminum metal (14), preferably in excess against stoichiometry with respect to the amount of antimony present, the treatment being preferably accompanied by stirring and cooling the reaction mixture to a temperature below 400° C, followed by separation of the dross (17) containing Al/Sb/As, which is formed during this treatment. 33. Process according to claim 32, wherein the second bottom product (13), after treatment with aluminium, and preferably also after removal of dross (17) containing Al/Sb/As, is treated with a third base (15), preferably selected from NaOH, Ca( OH) ₂ and Na ₂ CO ₃ and combinations thereof, more preferably NaOH, followed by separation of the base-containing dross (18) which is formed by this treatment. 34. The method according to claim 33, wherein the second bottom product (13), after treatment with the third base (15), is treated with sulfur (16), after which the dross (19) containing S, which is formed during this treatment, is separated. 35. The method according to any one of paragraphs. 1-34, in which at least part of the method is monitored and/or controlled electronically. 36. The metal composition obtained in the form of the first liquid discharge product (9), enriched with silver, by the method according to any one of paragraphs. 1-35, wherein the metal composition consists, on a dry weight basis, of: at least 6.0 wt.% and at most 27.5 wt.% lead; at least 72.5 wt.% and at most 91 wt.% tin; at least 95.0 wt.% and at most 99.0 wt.% lead and tin together; at least 0.75 wt.% and at most 4.50 wt.% silver; and at least 0.24 wt.% antimony, and which additionally also contains, on a dry weight basis: at least 0.05 wt.% and at most 0.5 wt.% arsenic; at least 0.05 wt.% and at most 0.6 wt.% copper; at least 0.0030 wt.% and at most 0.0500 wt.% nickel; at least 0.0010 wt.% and at most 0.40 wt.% bismuth; at most 1.0 wt% iron or at least 0.0005 wt% and preferably at most 0.0500% gold, while the rest are impurities. 37. The metal composition according to claim 36, which is a liquid melt.

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