RU2751202C1 - Method for processing gold-silver alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the metallurgy of precious metals and can be used in the refining processing of silver-containing raw materials (Dore alloys) with a gold content of up to 45%. Gold-silver alloys are leached in a nitric acid solution in the presence of oxygen supplied under pressure. Leaching is carried out at a temperature of 60-100°C and at vigorous stirring. The initial concentration of nitric acid in the solution is determined by calculation, with the provision of the final concentration of nitric acid in the solution from 50 to not less than 750 g / dm³, depending on the content of gold in the alloy.

EFFECT: invention provides the dissolution of silver over 95% of the original weight in the alloy, in which the gold content can reach 45%, at a maximum rate.

9 cl, 1 tbl, 15 ex

Description

The invention relates to the metallurgy of precious metals, in particular to methods of opening raw materials, and can be used in the refining processing of silver-containing raw materials (Dore alloys) with a content of up to 45% gold.

Dore alloys can be obtained both as the end result of processing ore raw materials and remelting secondary products - jewelry or technical scrap. The presence of more than 10% gold in them significantly complicates the refining of silver by the method of electrolytic refining in a nitric acid medium due to a significant drop in the rate of the process and the current efficiency. It is possible to carry out the separation of silver from gold by direct opening of the alloy in solutions of nitric acid. There is no description of specific dissolution conditions depending on the gold content in alloys in the technical and patent literature. It is known that the main technological disadvantage of the processes of dissolution of metals (including silver) in solutions of nitric acid is the release of significant volumes of nitrogen oxides that require disposal. To prevent their formation, there are methods based on the use of oxygen-containing oxidants.

In particular, the known "Method for the production of silver nitrate" [A.S. USSR No. 120327, class 40a 20 ₀₁ , "40a 22. Method for the production of silver nitrate / A.P. Amaryan, I.I. Galkin, V.I.Plyarpa, A.A. Remizova - No. 614499/22 dated 20.12.1958 ; publ. bulletin No. 11 for 1959 g -1 s.], including nitric acid dissolution of silver, in which, in order to increase the degree of use of nitric acid and prevent the release of nitrogen oxides, it is proposed to carry out the process in the presence of gaseous oxygen, ozone, or oxidants that do not introduce pollution into the system, for example, hydrogen peroxide The main disadvantage of this invention is that it has a narrow field of application - for the production of silver nitrate, and it does not consider the possibility of using the process in the processing of silver-containing raw materials containing gold.

Known "Process for refining silver bullion with gold separation" [2. Pat. US No. 6773487 B2 C01B 21/48. Process for refining silver bullion with gold separation / D. Vanhoutte, S. Brouver, UMICORE, Brussels - priority from 08.21.2003 No. 2003/0154821; publ. 08/10/2004 - 6 p.], Including the melting of a metal alloy with a flux in the form of silicon dioxide and borax, during which selenium and lead are removed from it; granulating the alloy in water; leaching the pellets in HNO ₃ , preferably in an atmosphere enriched in O ₂ ; filtration of the pulp with separation of the gold-containing base and its subsequent processing in a known manner, evaporation of the solution, followed by melting of the residue at a temperature of 220-350 ° C and denitration, which results in the formation of AgNO ₃ melt and denitration residue containing impurities mainly in the form of oxides; separation of the AgNO ₃ melt from the denitration residue. The disadvantage of the described process is the ability to use it to process alloys in which the permissible gold content is limited to 10%.

The closest in terms of the totality of features to the proposed solution is the "Method for producing nitric acid metal salt" [US Pat. RF No. 2038292, С01В 21/48; C01G 1/08. - Method of obtaining nitrate metal salt / R.I. Novoselov, E.V. Makotchenko - 5012265/26, announced on July 22, 1991; publ. 06/27/1995], including the dissolution of metal in a sealed container at an oxygen pressure of at least 0.15 atm when heated in nitric acid while passing oxygen and the subsequent isolation of the resulting salt. In this case, the metal can be: bismuth, cadmium, manganese, lead, iron, mercury, silver, etc. The main disadvantage of this method is the narrow scope of its applicability - for the production of nitric acid salts from metals (including silver) taken in pure form. To carry out the dissolution of any target component (for example, silver) from alloys, it is additionally required to find out the optimal conditions for the process, ensuring the most complete transfer of this component into solution.

The technical result, the achievement of which the present invention is directed, is the dissolution of more than 95% of silver from the original mass in the alloy, in which the gold content can reach 45%, at a maximum rate. In addition to silver and gold, the alloy may contain other components, in particular copper.

The achievement of the technical result is ensured by the fact that leaching in a nitric acid solution is carried out in the presence of oxygen supplied under pressure; intensive stirring, ensuring the absence of "dead zones" in the apparatus, while controlling the concentration of nitric acid in the solution, the final content of which should depend on the gold content in the original alloy. The dependence of the final concentration of nitric acid in the solution on the initial content of gold in the alloy, which ensures the extraction of more than 95% of silver into the solution, is presented in Table 1. The initial concentration of nitric acid in the solution is determined by calculation, based on the concentration of silver in the solution required by the technological conditions, and the reaction equations for the dissolution of silver:

The essence of the invention lies in the fact that in the method of processing silver-containing materials, the crushed (dispersed) gold-silver alloy is loaded into the reactor, water and non-concentrated nitric acid are fed in the proportions calculated according to Table 1 and equation 1, then the reactor is sealed, stirring is turned on and oxygen is supplied under pressure. The oxygen flow through the reactor is maintained throughout the entire process. The reactor is heated to a temperature of 60-100 ° C, kept until oxygen consumption stops, then cooled, and the gold-containing insoluble residue is separated from the solution. Refining of gold from the residue and silver from solution is carried out by known methods.

The need to supply oxygen under pressure and flow it through the reactor is due to the fact that the stable flow of dissolution according to equations (2-4) without the formation of nitrogen oxides:

possible only with constant direct contact of intermediate reaction products with oxygen. If, for some reason, the dissolution proceeded predominantly according to reaction (2), an increased pressure of nitrogen oxides can be created in the apparatus, which will block the flow of oxygen and the course of reactions 3 and 4.

The need for the presence of final concentrations of nitric acid, depending on the initial content of gold in the alloy to achieve high degrees of silver recovery, is due to the conditions for achieving thermodynamic equilibrium of the processes. When the gold content in the alloys is more than 45%, equilibrium is achieved even at low concentrations of silver in solutions, and the process stops.

The upper temperature limit (100 ° C) is due to the fact that at higher values, the partial pressure of water and nitric acid vapors over the solution increases significantly. In view of this, a higher oxygen pressure is required for the implementation of the process, which leads to a complication of the design of the apparatus in which the process is carried out.

The lower temperature limit (60 ° C) is due to the fact that the dissolution rate of silver, especially from alloys with a high gold content, decreases, which leads to incomplete transition of it into solution.

The method is carried out as follows: a solution of nitric acid with a concentration calculated according to table 1 and equation 1 is poured into the reactor and a crushed (dispersed) alloy containing silver and gold with a particle size of less than 500 microns is loaded. Then the reactor is sealed, stirring is turned on, oxygen is supplied. For alloys with a gold content of less than 20%, in order to avoid a premature start of the dissolution process, the dissolved alloy and water are initially charged into the reactor, and nitric acid is introduced last, after the oxygen supply has begun. Oxygen delivery rate is measured throughout the process. Maintaining a constant flow of oxygen through the solution (by means of a small discharge of off-gas), the reactor is heated to operating temperature. As soon as an increase in oxygen consumption associated with the onset of active dissolution of silver begins to be noted, the discharge of abgas is stopped. The dissolution is considered complete after the oxygen consumption in the reactor ceases. The resulting pulp is cooled, the gold-containing insoluble residue is separated from the solution. Refining of gold from the residue and silver from solution is carried out by known methods.

Below are examples of the implementation of the method.

Example 1.

80 g of an alloy of silver and gold (hereinafter referred to as an alloy) with a gold content of 45% was loaded into the reactor, 600 cm ³ of a nitric acid solution with a concentration of 800 g / dm ^{3 was} added, the reactor was sealed, stirring was turned on, and oxygen was supplied under a pressure of 0.5- 0.7 bar, the heating of the reactor was started. During heating, a small flow of oxygen through the reactor was maintained by venting off gas. At a temperature of 80-85 ° C, active dissolution of silver and absorption of oxygen began to occur, after which the discharge of abgas was stopped. After reaching the operating temperature of 90-100 ° C, the process was carried out until the cessation of oxygen consumption. The final concentration of HNO ₃ was 755 g / dm ³ , the extraction of silver into solution was 98.4%.

Example 2.

80 g of an alloy with a gold content of 40% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 500 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 90-100 ° C. The final concentration of HNO ₃ was 460 g / dm ³ , the extraction of silver into solution was 85.6%.

Example 3.

75 g of an alloy with a gold content of 32% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 550 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 85-90 ° C. The final concentration of HNO ₃ was 502 g / dm ³ , the extraction of silver into solution was 96.1%.

Example 4.

75 g of an alloy with a gold content of 32% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 330 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 85-90 ° C. The final concentration of HNO ₃ was 280 g / dm ³ , the extraction of silver into solution was 44.44%.

Example 5.

75 g of an alloy with a gold content of 28% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 250 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 80-85 ° C. The final concentration of HNO ₃ was 205 g / dm ³ , the extraction of silver into solution was 95.66%.

Example 6.

75 g of an alloy with a gold content of 23% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 230 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 75-80 ° C. The final concentration of HNO ₃ was 160 g / dm ³ , the extraction of silver into solution was 97.4%.

Example 7.

75 g of an alloy with a gold content of 23% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 180 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 75-80 ° C. The final concentration of HNO ₃ was 121 g / dm ³ , the extraction of silver into solution was 89.3%.

Example 8.

75 g of alloy with a gold content of 19% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 150 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 70-75 ° C. The final concentration of HNO ₃ was 105 g / dm ³ , the extraction of silver into solution was 96.3%.

Example 9.

75 g of alloy with a gold content of 19% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 100 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 70-75 ° C. The final concentration of HNO ₃ was 50 g / dm ³ , the extraction of silver into solution was 90.25%.

Example 10.

80 g of an alloy with a gold content of 13% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 90 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 60-70 ° C. The final concentration of HNO ₃ was 55 g / dm ³ , the extraction of silver into solution was 98.8%.

Example 11.

75 g of an alloy with a gold content of 13% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 50 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 60-70 ° C. The final concentration of HNO ₃ was 5 g / dm ³ , the extraction of silver into solution was 86.15%.

Example 12.

75 g of an alloy with a gold content of 28% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 210 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 90-100 ° C. The final concentration of HNO ₃ was 153 g / dm ³ , the extraction of silver into solution was 88.5%.

Example 13.

75 g of an alloy with a gold content of 40% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 700 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 90-100 ° C. The final concentration of HNO ₃ was 570 g / dm ³ , the extraction of silver into solution was 70.4%.

Example 14.

80 g of an alloy with a gold content of 28% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 250 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 50-55 ° C. The final concentration of HNO ₃ was 230 g / dm ³ , the extraction of silver into solution was 69.3%.

Example 15.

75 g of an alloy with a gold content of 40% was subjected to dissolution in 600 cm ³ of a nitric acid solution with a concentration of 800 g / dm ³ in the presence of oxygen supplied at a pressure of 0.5-0.7 bar in accordance with the above description. The operating temperature of the process was 50-55 ° C. The final concentration of HNO ₃ was 770 g / dm ³ , the extraction of silver into solution was 46.35%.

Claims (9)

1. A method of processing gold-silver alloys, including leaching in a solution of nitric acid in the presence of oxygen supplied under pressure, characterized in that the leaching is carried out at a temperature of 60-100 ° C and intensive stirring, and the initial concentration of nitric acid in the solution is determined by calculation , ensuring the final concentration of nitric acid in the solution from 50 to not less than 750 g / dm ³ , depending on the content of gold in the alloy. 2. The method according to claim 1, characterized in that the alloy is ground before leaching. 3. The method according to claim 1, characterized in that the oxygen supply is carried out at a pressure of 0.5-0.7 bar. 4. The method according to claim 1, characterized in that when the gold content is from 35 to 45%, the final concentration of nitric acid must be at least 750 g / dm ³ . 5. The method according to claim 1, characterized in that when the gold content is from 30 to 35%, the final concentration of nitric acid must be at least 500 g / dm ³ . 6. The method according to claim 1, characterized in that when the gold content is from 25 to 30%, the final concentration of nitric acid must be at least 200 g / dm ³ . 7. The method according to claim 1, characterized in that when the gold content is from 20 to 25%, the final concentration of nitric acid must be at least 150 g / dm ³ . 8. The method according to claim 1, characterized in that when the gold content is from 15 to 20%, the final concentration of nitric acid must be at least 100 g / dm ³ . 9. The method according to claim 1, characterized in that when the gold content is from 10 to 15%, the final concentration of nitric acid must be at least 50 g / dm ³ .