SU975821A1 - Method for recovering silver from palladium-containing alloys - Google Patents

Description

The invention relates to hydrometal-: lurgii non-ferrous metals and can be used in the refining of precious metals.

One of the tasks of metallurgy is to quickly return to industry with minimal losses of valuable metals from products that have completed their life. In particular, large amounts of recycled metals (scrap) containing palladium and silver in ratios of 1.5: 1 - 1: 2, often containing up to 20% copper, come into refining from the electronics industry enterprises. but

At a refining enterprise, silver ^{15 is} extracted from this type of raw material by the following method; the scrap is dissolved by heating in aqua regia and the silver chloride precipitate is separated from the solution. The silver chloride precipitate is "eametallic", i.e. reduced by iron. The recovered silver contains a significant amount of impurities, from which ciao?

2

They are naturally released during remelting, but most of the dirt remains in it.

A known method of extracting silver, which consists in the fact that the original product is chlorinated in a medium of hydrochloric acid, while the components forming soluble chlorides, go into solution, and silver is deposited in the form of chloride. The silver-rich precipitate is filtered off, washed with hot acidified water and leached silver with ammonia solution when heated. Silver chloride is precipitated from the ammonia solution with sulfuric or hydrochloric acid and is separated from the mother liquor. Silver chloride is expanded and, in aqueous pulp, silver £ 1, ^ is precipitated with an organic reducing agent or an electronegative element (iron or zinc).

This method has significant

disadvantages, the main of which are: the duration of the process, many 3, 975821 4

operational, high consumption of reagents, relatively low direct extraction of silver in the finished product.

The closest in technical essence is the method of extracting silver from palladium-containing alloys.

By a known method, the original alloy is dissolved in nitric acid. At the same time silver and other metals forming soluble nitrates, 10 for example palladium, copper, pigs, go into solution. Hydrochloric acid is introduced into the resulting solution until the release of silver chloride stops. The precipitate is separated, washed with hot acidified water, pulverized 15 in hydrochloric acid and, when heated, silver is reduced with metallic iron or zinc; the separated elemental silver is separated, washed, suc2iat [2 20

This method is also not free from drawbacks, among which it should be noted: the duration due to the presence of a significant number of operations, the need for heating during the precipitation stages. 25 In addition, the amount of hydrochloric acid injected should be approximately stoiometric, since its lack leads to incomplete extraction of silver chloride, and the excess leads to the transition of silver chloride 30 to the soluble complex and, consequently, to a decrease in the direct extraction of silver.

The aim of the invention is to intensify the process and increase the degree

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silver extraction.

This goal is achieved by the fact that according to the method of extracting silver from palladium-containing alloys, including the dissolution of the alloy in nitric acid and the isolation of silver solution by reducing ^, sodium hydroxide to pH 1-2 is introduced into the solution, ethylenediaminetetrauxonic acid disodium salt in a molar ratio to papa -,

-Gladium 1.1-1.5 and sulfuric acid to a concentration of 2-3-3M, and reduction is carried out by ferrocene, taken in a 1.5-2-fold excess of stoichiometry.

And also by the fact that the reduction leads to ferrocene in an organic solution, for example, in acetone or ethanol.

The essence of the method lies in the fact that ferrocene easily restores silver from „its nitrate:.

Α2 ·% + (Ο ^ ίς) ReС _b ⁵⁵

Studies have shown that the reaction rate (1) is very low, but it increases dramatically when sulfuric acid is introduced into the solution. Thus, when conducting the silver reduction process with a stoichiometric amount of ferrocene for 30 min, the degree of silver extraction was 6.6% at a concentration of sulfuric acid '(C _{M2% O4} ) = 0.01 M; 48.2% at = 0.1 M; 64.1% with Sc ^ SI "

= 1.0; 85.2% at C _{H (r9gch} = 2.0; 85.7% at C _{H / 2 о} -3.0; 85.5% at C = 4.0 and и86% at C _{AND (1} £ _O4 = 6.0.

As follows from the above data, _{Λ the} most optimal concentration of hydrochloric acid is 2-3 M.

Significantly affects the completeness of the extraction of silver and the amount of reducing agent - ferrocene. At the optimum concentration of the solution in sulfuric acid (2-ZM) with a molar ratio of ferrocent to silver equal to the stoichiometric in reaction (1), the degree of silver extraction is 85.7%; at 1.5: 1, the silver recovery rate is 99.3%; at 2.0: 1, the degree of extraction of silver is 99.5; at 3.0: 1, the silver recovery rate is 99.5%. Based on these experimental data, it is recommended that silver be reduced. 1.5-2.0 times the amount of ferrocene.

To prevent contamination of the precipitate of elemental silver with palladium, the nitrate solution is treated with a solution of sodium hydroxide before pH is set to pH 1-2 and the disodium EDTA is added in a molar ratio before precipitation of silver.

1.1-1.5 per palladium amount in solution. It was experimentally shown that with this acidity, palladium is part of a strong complex with EDTA, of 1: 1 composition, while silver is in solution in the form of nitrate.

Example 1. Palladium-silver alloy containing 20% palladium and 80% silver, weighing 100 g was dissolved in 0.3 l of 40% nitric acid. Crystalline caustic soda brought the acidity of the solution to a pH of 1.0 and introduced 105 g 'di-sodium salt of EDTA (ί, 5Μ EDTA / 1M

35 ml of 98% acid was added to the solution and 2.2 l of a 0.5 M solution of ferrocene in acetone (1.5 M of ferrocene / 1 M of silver) were introduced. After 30 minutes of stirring, the precipitate was filtered, washed with acetone, dried. The weight of the sediment was 76.2 g; according to the spectral analysis, it is represented by 95.3% Αβ ;.

Example 2. Palladium-silver alloy containing 30% palladium, 50%

975821

silver and 20% copper, weighing 100 g dissolved in 0.5 l of 30% nitric acid. Crystalline caustic soda brought the pH of the solution to 2.0 and introduced 116 g of disodium EDTA (1DMEDTA / 1M 5 Pc1). 82 ml of 98% sulfuric acid was added to the solution and 1.9 l of a 0.5 M solution of ferrocene in acetone (2, OM of ferrocene / 1 M silver) were introduced. After 30 minutes of stirring, the precipitate was filtered, washed with acetone, dried. The sediment weight was 49.6 g and, according to spectral analysis, it contains 99.9% silver. Thus, the extraction of silver amounted to 99.5%.

A comparison of the known method and the proposed one allows to conclude that the invention increases the direct extraction of silver from solution by 1.5-2%; reduces the duration of the process of 20 silver refining approximately 2.5 times; improves the quality of the target product; carried out at room temperature and does not require special equipment. 25

Claims (2)

Claim 1. The method of extracting silver from palladium-containing alloys, including dissolution of the alloy in nitric acid and the release of silver from solution by reduction, different hem, that, in order to intensify the process and increase the degree of silver recovery, sodium hydroxide is introduced into the solution to pH 1-2, ethylene diamine tetra acid disodium salt in a molar ratio to palladium 1.1-1.5 and sulfuric acid to a concentration of 2-ZM, and the reduction is carried out by ferrocene, taken in a 1.5-2 fold excess of stoichiometry. 2. The way pop. 1, characterized in that the recovery lead ferrocene in an organic solvent, for example in acetone or ethanol.