RU2779554C1 - Method for producing refined silver from intermediate products of precious metal production containing silver in the form of chloride - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the metallurgy of precious metals, in particular, to a method for refining silver. Production of refined silver from intermediate products of precious metal production containing silver in the form of chloride includes ammonia leaching, filtration, washing of the deposit, distillation of ammonia into the gas phase, forming silver chloride deposition, metallisation thereof and melting into ingots. The initial intermediate product of precious metal production undergoes reducing treatment in a hot alkaline solution at a temperature of 70 to 90°C and a pH=7 to 12 with a consumption of the reducing agent of 3 to 7% of the one stoichiometrically necessary for silver chloride reduction while ensuring that the redox potential of the system is at the level of 100 to 300 mV relative to the silver chloride electrode. Two cycles of hydrometallurgical processing are then performed in sequence, wherein each cycle consists of ammonia leaching at a temperature of 20 to 40°C, at a concentration of free ammonia of 15 to 25%, for 1 to 4 hours; distillation of ammonia with evaporation of the solution under vacuum or at the boiling point of the solution with absorption of the resulting vapour-gas phase by circulating ammonia solutions; and hydrochloric acid leaching of the silver chloride deposit formed at the stage of distillation of ammonia in a solution at a concentration of HCl=10 to 150 g/dm³, at a temperature of 40 to 90°C, for 1 to 3 hours. The filtered and washed silver chloride is metallised at a temperature of 40 to 90°C, a pH=7-12, initial L:S ratio of 2 to 5 for 2 to 4 hours using an organic reducing agent, then melted into ingots of refined silver with the addition of a fluxing agent, wherein sodium hydroxide is used as said agent.

EFFECT: possibility of reducing the consumption of reagents, lowering the fault rate of silver by impurities of platinum metals due to the reduction thereof to a metallic state and the removal from the process chain at head operations of the process diagram.

6 cl, 1 dwg, 3 tbl, 2 ex

Description

The invention relates to the metallurgy of precious metals, in particular to a method for refining silver.

To date, the main method for obtaining refined silver is electrolytic. Moreover, it is implemented in two versions: electrorefining of silver anodes (Maslenitsky I.N., Chugaev L.G. Metallurgy of noble metals. - M .: Metallurgy, 1987. - 366 p., Metallurgy of noble metals: in 2 books. Book 1 / Yu.A. Kotlyar, M.A. Meretukov, L.S. Strizhko. - M.: MISIS, "Ore and metals", 2005., - 432 p., Meretukov M.A., Orlov A.M. Metallurgy of noble metals. Foreign experience. - M.: Metallurgiya, 1990. - 416 p.) and the method of electroextraction of silver from a solution of its nitrate in electrolyzers with insoluble anodes (S.A. Mastyugin, N.A. Volkova, S.S. Naboichenko, M.A. Lastochkina Sludges from electrolytic refining of copper and nickel: monograph Ekaterinburg: URFU 2013.274 p., RF patent 2650372).

In the first case, the source materials - metallized silver-containing middlings, copper electrorefining sludge, after removing copper and selenium from them, are melted to obtain silver anodes (silver-gold; gold content in the anode metal up to 20% does not disturb the electrolysis). Melting conditions are determined by the composition of the source material and are selected based on the maximum possible removal of impurities into slags (lead, antimony, arsenic, silicon dioxide, copper, tellurium, etc.) and gases (selenium).

In the process of electrochemical dissolution of silver anodes, silver and more electronegative impurities pass into the electrolyte, gold and a significant part of the platinum metals form a sludge, and silver is deposited on the cathode in the form of a coarse-grained precipitate.

To prevent excessive accumulation of impurities in the electrolyte, part of it is removed from the technological cycle, and after cleaning it is returned to the process; periodically, the electrolyte is completely replaced, for which part of the cathode silver is dissolved in nitric acid, and silver is removed from the spent electrolyte to be returned to the circuit, and the solution with impurities is sent for disposal.

The process is characterized by a long technological cycle, significant circulation of silver with anode scrap, the formation of nitrogen oxides during the preparation of fresh electrolyte and electrorefining, as well as the use of manual labor for loading anodes and unloading anode sludge.

When obtaining refined silver by electrolysis with insoluble anodes (electroextraction), a silver-gold alloy or other metallized product is dissolved in nitric acid to obtain a solution of silver nitrate and impurities, which is then purified and transferred to electrolysis.

Unlike the method described above, the process of obtaining refined silver by electroextraction from silver nitrate solutions due to the absence of anode scrap is characterized by a reduced volume of work in progress (WIP) and the share of manual labor, however, it is also associated with the formation of nitrogen oxides during the preparation of the electrolyte and, accordingly, the need operation of a bulky gas cleaning system.

A known method of obtaining refined silver by processing refining middlings containing silver in the form of chloride (Metallurgy of noble metals / Edited by L.V. Chugaev. M.: Metallurgy, 1987, S. 315-327). It includes the treatment of silver-containing materials with an aqueous solution of sodium chlorate in the presence of HCl to leach impurities of copper, lead and sodium, the reduction of purified silver chloride to metal with zinc powder, washing, drying and remelting sponge silver into anodes for subsequent electrolytic refining. After remelting cathode silver, a metal containing 99.98% Ag is obtained. The disadvantage of this method is the long duration of the technological cycle, the alternation of pyro- and hydrometallurgical operations, which makes it impossible to create a continuously operating automated technological chain.

A known method of extracting palladium, gold and silver (RJ. Metallurgy. 1984, 8G343P), including processing the material with aqua regia, separating silver in the form of chloride, drying and melting the latter with Na ₂ CO ₃ at 850 ° C to obtain spongy silver, dissolving the latter in HNO ₃ , separating Ag ₂ O with sodium hydroxide solution, drying and calcining the precipitate at 400°C to obtain sponge silver of high purity (99.96%). The disadvantage of this method is the long duration of the technological cycle, the possible loss of silver with sublimates, the alternation of pyro- and hydrometallurgical operations, which makes it impossible to create a continuously operating automated technological chain, as well as the need to organize a cumbersome gas cleaning system due to the release of nitrogen oxides when dissolving sponge silver in nitric acid. .

A known method (Patent RU No. 2049131) for obtaining refined silver from middlings containing silver chloride, including reduction with iron powder in hydrochloric acid solution with a pH of 3.0-3.2, treatment of the precipitate with a solution of sodium hydroxide to convert residual silver chloride into its oxide (hydroxide), and then dissolving it in nitric acid to obtain a solution of silver nitrate. To remove impurities, the solution is treated with a sodium hydroxide solution to pH 6-6.5, which ensures hydrolysis and precipitation of the main amount of impurities, which is filtered out. Then sodium nitrite is introduced into the filtrate purified from impurities to precipitate silver in the form of nitrite, which is filtered off. The solution containing impurities is withdrawn from the technological cycle, and silver nitrite is boiled in a sodium hydroxide solution at pH 11.5-12.5, as a result of which it is completely converted into oxide. The alkaline solution of sodium nitrite obtained at this stage is used to precipitate silver nitrite, and the silver oxide after washing from the mother liquor is dried and reduced to obtain refined silver. The disadvantage of this method is the use of the operation of dissolving the precipitate in nitric acid, accompanied by the formation of nitrogen oxides, which requires the organization of a bulky gas cleaning system.

A known method of extracting silver from copper electrorefining sludge (US Patent No. 3658510), including ammonia leaching of the sludge hydrochlorination residue, boiling the solution to remove ammonia and forming a precipitate of pure silver chloride.

According to the invention, the sludge is chlorinated in 8-9 N hydrochloric acid, preferably 12 N, in a reflux reactor, which minimizes the loss of acid in the off-gases. The pulp obtained during chlorination is filtered. The solution containing selenium, tellurium, other precious metals and impurities is separated by filtration. The precipitate for dissolving the residual lead chloride is subjected to leaching with a hot solution acidified with hydrochloric acid (pH 0.5-5) at W:T ~ 10 for 1 hour, the resulting pulp is thickened in the presence of a flocculant, and then filtered.

Further, the resulting precipitate is pulped in water with the addition of concentrated ammonia. The range of ammonia content in the finished pulp is quite wide and is 2-5 N, while the estimated amount of ammonia is from 1-1.5 g/g of dry residue from the previous stage. Ammonia leaching is carried out in the cold (at room temperature) for 1 hour.

Next, the leached pulp is filtered, the precipitate is washed with water and then removed from the process flow, and the solution combined with the washing water is transferred to heat treatment to strip ammonia into the gas phase and form a silver chloride precipitate.

The process is carried out at the boiling temperature and ends when it reaches ~ 100°C, which indicates the almost complete removal of ammonia into the gas phase.

An alternative to boiling may be to acidify the ammonia leach solution with sulfuric or nitric acid.

Next, the resulting pure silver chloride is treated with a hot solution of sodium hydroxide with vigorous stirring to convert it into hydroxide, and then a concentrated glucose solution is introduced to obtain metallic silver. Other organic reducing agents may also be used. The melting of the obtained silver powder is carried out under oxidizing conditions, which ensures the removal of organic impurities. The disadvantage of this method is the increased risk of silver contamination with impurities that form complex compounds with ammonia - copper, nickel, cobalt, zinc, and platinum metals due to the receipt of ammonia leaching with the remains of an unwashed hydrochlorination solution, as well as the inability to regenerate ammonia. The method described above is the closest to the claimed, so selected as the closest analogue.

The objective of the proposed method is to obtain refined silver in the form of ingots.

The technical result from the implementation of the method for obtaining refined silver is to increase the culture of production by eliminating periodic processes accompanied by manual labor, reducing the consumption of reagents due to their regeneration, as well as enabling the creation of a continuously operating automated hydrometallurgical process chain and reducing the risk of silver rejects due to impurities. platinum metals due to their reduction to the metallic state and removal from the technological chain at the head operations of the technological scheme.

The technical result is achieved by the fact that in the proposed method for obtaining refined silver, including ammonia leaching, filtration, washing of the precipitate, stripping of ammonia into the gas phase with the formation of a precipitate of silver chloride, its metallization and melting into ingots, according to the method, the initial intermediate product of precious metal production containing silver in the form of chloride, subjected to reduction treatment in a hot alkaline solution at a temperature of 70-90 ° C and pH = 7-12 at a reducing agent consumption of 3-7% of the stoichiometrically necessary for the reduction of silver chloride while ensuring the redox potential of the system at the level of 100-300 mV relative to the silver chloride electrode, then two cycles of hydrometallurgical treatment are sequentially carried out, each of which consists of ammonia leaching at a temperature of 20-40 ° C, a free ammonia concentration of 15-25% for 1-4 hours, ammonia stripping by evaporating the solution under vacuum or at temperature boiling of the solution with absorption of the resulting gas-vapor phase by circulating ammonia solutions, hydrochloric acid leaching of the precipitate of silver chloride formed at the stage of ammonia distillation in solution at a concentration of HCl=10-150 g/dm ³ , at a temperature of 40-90°C for 1-3 hours, after whereupon the filtered and washed silver chloride is metallized at a temperature of 40-90°C, pH=7-12, initial W:T 2-5 for 2-4 hours using an organic reducing agent, and then melted into ingots of refined silver with the addition of a fluxing agent .

Sodium formate, formic acid, hydrazine hydrate, etc. can be used as a reducing agent.

As a liquid phase for the recovery treatment, it is possible to use water or a circulating solution from the stage of metallization of pure silver chloride.

As a liquid phase for ammonia leaching, a circulating ammonia solution from the ammonia stripping stage is used.

As the initial solution for hydrochloric acid leaching of the first cycle, a solution from hydrochloric acid leaching of the second cycle is used with the necessary replenishment of water and hydrochloric acid.

In the proposed method, the ammonia absorption circuit is fed with water or silver chloride pulp filtration solutions.

Also in the method, the cycle of ammonia leaching, ammonia stripping and hydrochloric acid leaching of the formed silver chloride is carried out twice.

In the proposed method, when melting refined silver ingots, sodium hydroxide is used as a fluxing agent.

Also in the proposed method, as an additional source of alkali at the stage of metallization of silver chloride, it is possible to use slag from melting metallized silver chloride into ingots.

The essence of the proposed method is as follows.

The process was carried out according to the scheme shown in figure 1.

The insoluble hydrochlorination residue (HO) of the precious metal concentrate containing silver chloride, oxides of silicon, calcium, base metal compounds or other silver concentrate based on its chloride is treated with a hot (70-90 ° C) alkaline (pH = 7-12) solution of a reducing agent ( sodium formate, formic acid, hydrazine hydrate, etc.) to restore the platinum metal complexes adsorbed on the surface of silver chloride to the metallic state (operation 1, figure 1).

As a liquid phase, water with the addition of a reducing agent and alkali, or a solution from the plating of pure silver chloride (product 10.1, figure 1) can be used.

When carrying out the process, small amounts of a reducing agent (not more than 3-7% of stoichiometry) are used, which are dosed to maintain the redox potential of the system (ORP) at a level of 100-300 mV relative to the silver chloride electrode.

An increase in the consumption of the reducing agent by more than 3-7% of the stoichiometry will lead to an increase in the degree of metallization of silver chloride, which will lead to a decrease in its extraction into the solution at the stage of ammonia leaching, both by increasing the proportion of metallic silver that is stable in ammonia solutions, and by passivating the surface silver chloride film of metallic silver. A lower consumption of the reducing agent will not provide the required degree of reduction of the platinum metal complexes adsorbed by the silver chloride surface.

Reducing the ORP below 100 mV will lead to excessive consumption of the reducing agent and an increase in the degree of metallization of silver chloride, which is undesirable.

Carrying out the process at an ORP of the system of more than 300 mV will not provide the required depth of reduction of platinum metals and may lead to the rejection of refined silver.

Carrying out the process at a temperature below 70°C can lead to a decrease in the completeness of the reduction of platinum metals, an increase of more than 90°C - to additional energy consumption.

Maintaining the recommended pH range of the medium is necessary to ensure the speed and completeness of metallization of platinum metal compounds. The transition to the acidic region (pH<7) will lead to their insufficient recovery, and, accordingly, contamination of the commercial metal, excessive alkalization (pH>12) will not improve the process performance, but will entail an increase in the consumption of reagents.

At the end of the process, the resulting pulp is filtered (centrifuged), the precipitate (product 1.1, figure 1) is sent for ammonia treatment in the ammonia circulating solution, and the solution (product 1.2, figure 1) is sent for waste disposal. Washing the precipitate to remove the components of the solution is an optional operation, since the process of reductive treatment is not accompanied by a noticeable extraction of the components of the precipitate into the solution, and contamination of the precipitate of the refined silver with the components of the solution is unlikely.

In the process of the first ammonia treatment - leaching (operation 2, figure 1), implemented at a temperature of 20-40 ° C, a concentration of free ammonia of 15-25% for 1-4 hours, the dissolution reaction of silver chloride develops with the formation of an ammonia complex, solubility which is determined by the concentration of free ammonia in solution (table 1).

The ratio of liquid and solid is determined by the equilibrium concentration of silver in the solution, which is determined by the content of free ammonia in the leaching solution.

Hydroxides and basic salts of non-ferrous metals present in the composition of the reductive leaching cake, which can form complex compounds with ammonia (copper, nickel, cobalt, zinc), can also be extracted into the solution. Lead, which has amphoteric properties, can also partially pass into solution due to the formation of plumbate ions.

Increasing the leaching temperature above 30-40°C leads to an increase in ammonia losses with the vapor-gas phase, a decrease in the stability of silver ammonia complexes and an increased transition of feedstock components capable of dissolving in alkaline media (silicon dioxide, aluminum oxide, lead oxide, etc.) .).

A decrease below 20-22°C will require the use of special refrigeration units, which will lead to increased energy consumption.

An increase in the ammonia concentration in the solution above 25% will entail a complication of the instrumentation of the process due to the high vapor pressure of ammonia over its concentrated solutions even at room temperature, a decrease below 15% will require an increase in the ratio of liquid and solid at the leaching stage to ensure the possibility of obtaining stable solutions and high extraction of silver at the stage of ammonia leaching from its chloride.

Reducing the duration of ammonia leaching to less than 1 hour will lead to incomplete extraction of silver chloride, an increase of more than 4 hours will lead to increased losses of ammonia from the gas-vapor phase.

Compounds insoluble in ammonia - oxides of silicon, calcium, metallic and chalcogenide forms of non-ferrous metals, their oxides, metallized forms of precious metals - form a cake (product 2.1. figure 1), which is filtered at the end of the process. The solution together with washing water (product 2.2, figure 1) is sent to obtain silver chloride, the insoluble residue is transferred to the extraction of platinum metals by known methods (for example, melting with other refining wastes).

The extraction of silver from the ammonia solution is based on the decrease in the stability of the ammonia silver complex with a decrease in the concentration of free ammonia. This can be realized by its distillation with water vapor, either under vacuum or at elevated temperature, preferably close to the boiling point of the solution (operation 3, figure 1).

Evaporation is carried out until the main amount of ammonia passes into the gas phase, and the ammonia complex of silver does not decompose.

The resulting gas-vapor phase, containing in its composition water vapor and ammonia, is absorbed by the circulating ammonia solution, which, as necessary, is removed for ammonia leaching (product 3.1, figure 1).

To eliminate the need to use pressure equipment, the concentration of free ammonia in absorption solutions should not exceed 25% (wt.), For which the circulating ammonia solution used for ammonia absorption is diluted with a part of the solution (product 4.2, figure 1) obtained by filtration of silver chloride pulp.

Water can also be used as the liquid phase.

Another option to ensure the necessary water balance of the process is to remove water by evaporating the solution of ammonia leaching of silver in the required amount to obtain a maximum of 25% ammonia solution in the absorption of the gas-vapor phase.

Upon completion of evaporation, the silver chloride pulp is filtered (centrifuged, thickened). Silver chloride 1 (product 4.1, figure 1) and part of the filtered solution (product 4.2, figure 1) is treated with a hot circulating hydrochloric acid solution (product 9.1, figure 1) to bind the residual amount of ammonia present in the ammonia complexes of non-ferrous metals and silver into the form ammonium chloride, and non-ferrous metals - in the form of water-soluble chlorides.

The use of hydrochloric acid leaching contributes to the effective purification of silver chloride from non-ferrous metals that have precipitated silver chloride (product 4.1, figure 1) in the form of sparingly soluble hydroxides during the decomposition of their ammonia complexes.

Leaching is carried out in a recycled hydrochloric acid solution at a concentration of HCl=10-150 g/DM ³ at a temperature of 40-90°C for 1-3 hours.

An increase in the concentration of hydrochloric acid over 150 g/dm ³ during repulpation does not provide a more complete extraction of non-ferrous metals into the solution, however, it can lead to an increased recovery of silver into the solution due to the formation of soluble chloride complexes at a high chloride background.

The concentration of hydrochloric acid below 10 g/DM ³ does not provide effective dissolution of non-ferrous metal hydroxides and leads to a more dirty precipitate. Lowering the leaching temperature below 40°C and carrying out the process for less than 1 hour has a similar effect.

Increasing the temperature above 90°C will lead to increased energy consumption without improving the performance of the separation of non-ferrous metals and silver.

At the end of hydrochloric acid leaching (operation 5, figure 1), the pulp is filtered, the precipitate (product 5.2, figure 1) is washed with water. The solution combined with wash water (product 5.1, figure 1) is transferred to waste disposal, which provides the organization of a channel for removing impurities from the process flow.

Obtained by a combination of operations 1-5, silver chloride (product 5.2, figure 1) to ensure a stable composition of the final refined metal is additionally refined in a similar way and only then is metallized and melted into ingots.

Thus, the technological scheme for the processing of silver concentrates containing silver in the form of chloride includes two consecutive cycles of hydrometallurgical processing, each of which includes ammonia leaching, decomposition of the ammonia solution and hydrochloric acid leaching of the formed silver chloride precipitate, as well as auxiliary operations - filtration (centrifugation), washing of sediments.

The parameters for carrying out ammonia leaching (operation 6, figure 1) and decomposition of the ammonia solution (operation 7, figure 1) of the second cycle are carried out under conditions similar to those for the first cycle (operations 2 and 3, respectively).

Silver chloride (product 5.2, figure 1) is dissolved in the circulating ammonia solution 7.1 (operation 6, figure 1). The resulting solution containing a certain amount of suspension is filtered to separate it. The precipitate (product 6.1, figure 1) without washing is transferred to the first stage of ammonia treatment (leaching) (operation 2, figure 1) to recover silver from it and organize a single channel for removing platinum metal impurities from the technological cycle.

The solution (product 6.2, figure 1) is transferred to evaporation to decompose the ammonia complexes of silver present in its composition and regenerate ammonia to obtain a circulating ammonia solution 2 (product 8.2, figure 1), which is used in the second stage of ammonia leaching (operation 6, figure 1 ).

The pulp formed during evaporation of silver chloride (product 7.2, figure 1) is filtered, the cake (product 8.1, figure 1) is washed with water and fed to hydrochloric acid leaching (operation 9, figure 1), which is carried out under the same process parameters as operation 5 , but using pure hydrochloric acid solution (10-150 g/dm ³ HCl, temperature 40-90°C, duration 1-3 hours).

At the end of hydrochloric acid leaching, the pulp is filtered (centrifuged), the solution combined with washing water (product 9.1, figure 1) is sent into circulation for hydrochloric acid leaching of the first silver chloride (operation 5, figure 1), the washed silver chloride is metallized (operation 10, figure 1) and melting into ingots (operation 11, figure 1).

Metallization is carried out in a stirred reactor at a temperature of 40-90°C, pH=7-12, initial W:T 2-5 for 2-4 hours using an organic reducing agent, for example, hydrazine hydrate in an amount of 100-110% from the stoichiometrically necessary.

During the metallization process, the following reaction develops:

Lowering the temperature below 40°C and duration less than 2 hours will reduce the depth of reduction of silver chloride, which will lead to an increased yield of slag at the stage of melting the metallized residue into ingots.

An increase above 90° C. will result in increased energy costs without improving process performance.

Excessive delay of the process (more than 4 hours) will have a similar effect, in addition, with a significant reduction time, the likelihood of the formation of powder conglomerates increases, which can lead to equipment malfunctions.

Upon completion of the metallization, the pulp is filtered, the precipitate is washed with distilled water. The solution combined with the wash water (product 10.1) is either transferred to waste disposal, or to optimize the water balance of the process, it can be fed to the stage of recovery processing of the original silver concentrate.

The filtered and washed precipitate of metallic silver (product 10.2, figure 1) is then melted into ingots with the addition of sodium hydroxide as a fluxing agent in the amount of 50-200 g/kg of the metallized residue.

An increase in the consumption of sodium hydroxide in excess of the specified values will lead to an increased yield of slag to be disposed of, a decrease - to possible losses of silver with sublimations of its chloride.

The slag obtained as a result of smelting (product 11.2, figure 1) can be transferred for the additional extraction of precious metals, with other precious metal-containing refining wastes, for example, sediments from the decontamination of mother liquors, insoluble residues from the hydrochlorination of concentrates, etc., or after crushing and grinding, it is used in the cycle the production of refined silver as an additional source of alkali in operation 11, figure 1. In this case, the silver present in its composition will be extracted along the shortest possible chain and transferred to the refined metal.

The present invention is illustrated by the following figures:

1. Figure 1 - is a diagram of obtaining refined silver according to the claimed method (dotted lines show possible options for recycling products).

The proposed method is also illustrated by the following examples.

Example 1 (according to the closest analogue).

The initial middling product of precious metal production, containing silver in the form of chloride, was processed according to the method described in the closest analogue. The sequence of operations included:

1. Hydrochlorination in a solution of hydrochloric acid with a concentration of 5N at a temperature of 70-80°C for 1 hour, filtering the precipitate;

2. Leaching with an acidified hydrochloric acid solution at a temperature of 70-80°C for 1 hour, filtration, washing;

3. Ammonia leaching of the precipitate in an ammonia solution with an initial concentration of 15N at room temperature for 1 hour at an initial ratio of liquid and solid 18 (compared to the closest analogue, the ratio of liquid and solid at the stage of ammonia leaching was increased to obtain stable solutions), filtration , washing;

4. Distillation of ammonia from the filtered solution during evaporation until the temperature stabilizes at 100°C, filtering the silver chloride pulp;

5. Recovery in an alkaline solution with dextrose at an initial concentration of sodium hydroxide 115 g/DM ³ at 80-90°C for 2 hours, filtering, washing;

6. Melting into ingots.

The results of the experiments are presented in table 2.

Example 2 (according to the claimed method)

The initial middling product of precious metal production, containing silver in the form of chloride, was processed, according to the claimed method, as follows:

1. Reduced in an alkaline solution at pH 12 with sodium formate at a temperature of 70-80°C for 2 hours at a reducing agent consumption of 6.7% of the stoichiometrically required for the reduction of silver chloride to metal while maintaining the ORP of the system at a level of 200 mV relative to the silver chloride electrode; the precipitate was filtered, washed with water;

2. Leached in an ammonia solution with a concentration of 25% at room temperature for 1 hour, the pulp was filtered, the precipitate was washed with water;

3. The ammonia solution was evaporated with the absorption of the gas-vapor phase by an ammonia solution with a concentration of 15%; the resulting pulp of silver chloride was filtered, washed with water;

4. The precipitate of silver chloride was leached with a hydrochloric acid solution with a concentration of 50 g/DM ³ at a temperature of 70-80°C for 1 hour; the resulting pulp was filtered, the precipitate was washed with water;

5. The washed precipitate of silver chloride was divided into two parts, which were processed as follows:

a. the first part was reduced in an alkaline solution with hydrazine hydrate at a temperature of 70-80°C, pH ~ 12 for 2 hours; the resulting pulp was filtered, the precipitate was washed with water, and then melted with the addition of sodium hydroxide;

b. the second part was redissolved in an ammonia solution (the material was completely dissolved), the solution was filtered to control the content of the suspension in it, and then evaporated. The resulting gas-vapor phase was absorbed with an ammonia solution with a concentration of 15%, the distillation pulp was filtered, the precipitate was washed with water, and then leached in a hydrochloric acid solution with a concentration of 50 g/DM ³ at a temperature of 70-80°C for 1 hour; the resulting pulp was filtered, the precipitate was washed with water, then metallized in an alkaline solution with hydrazine hydrate at a temperature of 70-80°C, pH ~ 12 for 2 hours; the resulting pulp was filtered, the precipitate was washed with water, and then melted with the addition of sodium hydroxide. The results of the experiments are presented in table 3.

From tables 2 and 3, the claimed method provides the possibility of stable production of refined silver of the highest grades from intermediate products of precious metal production, containing, along with silver in the form of chloride, platinum metals.

The second undoubted advantage of the proposed method is the possibility of regeneration of the main amount of ammonia due to the absorption of the vapor-gas mixture formed during the evaporation of ammonia solutions with circulating ammonia solutions. This circumstance will allow not only to reduce the cost of purchasing reagents, but also to increase the environmental friendliness of production due to the reuse of ammonia in the technological scheme.

With regard to the extraction of silver into solution at the stage of ammonia leaching, both methods provide comparable performance at a level of more than 98%. The remaining amount of silver is not lost, but is returned along with the sediment of other precious metals to the technological cycle and is additionally recovered during its processing.

Thus, the proposed method allows the processing of silver concentrates containing silver in the form of chloride, due to reduction processing, two successive cycles of hydrometallurgical processing, each of which includes ammonia leaching, decomposition of an ammonia solution and hydrochloric acid leaching of the formed precipitate of silver chloride, and also auxiliary operations - filtration (centrifugation), washing of precipitates and obtaining refined silver in ingots.

Claims (6)

1. A method for obtaining refined silver from intermediate products of precious metal production containing silver in the form of chloride, including ammonia leaching, filtration, washing of the precipitate, stripping of ammonia into the gas phase with the formation of a precipitate of silver chloride, its metallization and smelting into ingots, characterized in that the original intermediate product precious metal production, containing silver in the form of chloride, is subjected to reduction treatment in a hot alkaline solution at a temperature of 70-90 ° C and pH = 7-12 at a reducing agent consumption of 3-7% of the stoichiometrically necessary for the reduction of silver chloride while ensuring the redox potential of the system at a level of 100-300 mV relative to the silver chloride electrode, then two cycles of hydrometallurgical treatment are sequentially carried out, each of which consists of ammonia leaching at a temperature of 20-40 ° C, a free ammonia concentration of 15-25%, a duration of 1-4 hours, ammonia stripping at evaporation of the solution under vacuum or at the boiling point of the solution with absorption of the resulting gas-vapor phase by circulating ammonia solutions, hydrochloric acid leaching of the precipitate of silver chloride formed at the stage of ammonia distillation in solution at a concentration of HCl=10-150 g/dm ³ , at a temperature of 40-90°C for 1- 3 hours, after which the filtered and washed silver chloride is metallized at a temperature of 40-90 ° C, pH = 7-12, initial W: T 2-5 for 2-4 hours using an organic reducing agent, and then melted into ingots of refined silver with the addition of a fluxing agent, which is sodium hydroxide. 2. The method according to p. 1, characterized in that sodium formate, formic acid, hydrazine hydrate are used as a reducing agent. 3. The method according to claim 1, characterized in that water or a circulating solution from the stage of metallization of pure silver chloride is used as an alkaline solution for the reduction treatment. 4. The method according to p. 1, characterized in that as a leaching solution for ammonia leaching, a circulating ammonia solution from the ammonia stripping stage is used. 5. The method according to claim 1, characterized in that as a leaching solution for hydrochloric acid leaching of the first cycle, a solution from hydrochloric acid leaching of the second cycle is used with the necessary replenishment of water and hydrochloric acid. 6. The method according to p. 1, characterized in that as an additional source of alkali at the stage of metallization of silver chloride, slag is used for melting metallized silver chloride into ingots.

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