RU2103396C1 - Method of reprocessing middlings-solutions of platinum group metal affinage processes - Google Patents

Abstract

FIELD: precious metal metallurgy. SUBSTANCE: method can be used in affinage production of platinum group metals involving simultaneously occurring palladium and rhodium conversions. Method utilizes side product obtained in preparation of palladium from tetraamminopalladium chloride, mother solution from ammonia-mediated palladosammine precipitation step, to form reagent replacing ammonium chloride when precipitating rhodium ammonium-sodium hexanitrite in the process of rhodium affinage. Ammonium chloride solution substitute is prepared by treating above-mentioned mother solution to achieve pH value within the range from 1 to 5, separating salt precipitate, and optional evaporation of solution. When using reagent of invention, quality of final product does not worsen. EFFECT: reduced cost of affinage process. 2 cl, 2 tbl

Description

 A method of processing solutions - industrial products of refining production relates to the field of metallurgy, in particular noble metals. The method can be used in the refining production of metals of the platinum group (PGM), which has at the same time operating limits for the production of palladium and rhodium.

 The technological schemes for the refining of metals of the platinum group (PGM) include the operations of obtaining and processing various solutions - intermediate products of the refining production of PGM from raw materials containing palladium and rhodium, are the following two.

1. At the stage of obtaining rhodium - a solution containing rhodium in the form of sodium hexanitrite rhodium Na ₃ Rh (NO ₂ ).

2. At the stage of obtaining palladium - a solution containing a water-soluble palladium salt - tetramine palladochloride (NH ₃ ) ₄ PdCl ₄ .

 Processing of these two types of solutions according to the literature. Metallurgy of precious metals. / Ed. Chugaeva L.V., - M.1987 (p. 408-415) includes the solid separation of those compounds from which purified individual metals of the platinum group can be obtained.

As precipitated forms (compounds) use:
for the isolation of palladium palladosammine (PZA) - (NH ₃ ) ₂ PdCl ₂ , hydrochloric acid is used as a reagent for the PZA precipitator [p. 415],
to isolate rhodium, ammonium sodium hexanitrite rhodium (rhodium ANG) - (NH ₄ ) ₂ NaRh (NO ₂ ) ₆ ; ammonium chloride is used as a precipitating agent of rhodium ANG (p. 412).

 The mother liquors from the precipitation of PZA and ANG of rhodium go through the stage of additional extraction of residual PGM using the cementation process with base elements (p. 415).

 The specified method of processing solutions of industrial products of refining production is the closest to the claimed.

The disadvantages of the prototype method of processing varieties of solutions of refining production are:
high consumption of ammonium chloride reagent for the deposition of angium rhodium,
the formation in the redistribution of obtaining palladium and rhodium a large volume of uterine solutions subjected to cementation,
the formation of a large volume of industrial stocks with which a certain amount of PGM and ammonium chloride is irretrievably lost.

 The alleged invention is aimed at solving the problems of reducing the consumption of ammonium chloride, reducing the formation of industrial waste and reducing the loss of PGM.

 The problem is solved in that the acidic mother liquor obtained by precipitation of palladosammine from a solution of tetramine palladochloride is neutralized with ammonia until a pH of 1-5 is established, the neutralized solution is filtered off from the precipitate, the filtrate is used as ammonium chloride for precipitation of rhodium angiamine.

 The essence of the alleged invention is as follows.

During the precipitation of palladosammine from a solution of tetramine palladochloride by treatment with hydrochloric acid in the mother liquor, ammonium chloride is generated by the reaction:
[Pd (NH ₃ ) ₄ ] Cl ₂ + HCl = (NH ₃ ) ₂ Cl ₂ Pd + 2 NH ₄ Cl. (1)
Thus, in the process of refining palladium, a solution is formed containing the reagent necessary for use in the deposition of rhodium. However, this solution contains, in addition to ammonium chloride, also hydrochloric acid, since the completeness of precipitation and the required purity of palladosmine from a solution of tetramine palladochloride are ensured by using an excess of hydrochloric acid in addition to stoichiometry of reaction (1). As experimental studies have shown, due to the presence of hydrochloric acid, platinum and palladium compounds, as well as base elements in an acidic mother liquor, the use of it as a reagent for the precipitation of ANG would lead to a decrease in the extraction of rhodium in the precipitate by contamination of the resulting rhodium salt with impurities.

The introduction according to the invention of additional operations of processing the mother liquor of PZA with ammonia until the establishment of a ZR in the range from 1 to 5 and filtering the precipitate formed allows:
neutralize hydrochloric acid while increasing the concentration of ammonium chloride in the solution,
isolate a significant part of platinum, palladium and a certain amount of base elements in the sediment, and the impurities remaining in the filtrate should be in the form of such complexes that are not coprecipitated with ANG.

An increase in the concentration of ammonium chloride in a neutralized solution occurs due to the reaction:
HCl + NH ₃ = NH ₄ Cl. (2).

 Base metals, as a result of neutralization of the acidic uterine PZA, until a PH is established in the range of 1--5, precipitate hydroxides, palladium in this case precipitates mainly in the form of chlorammiamic compounds of the type (NH3) 2 PdCl2, and platinum, apparently, in the form of chloramonium compounds.

 The proposed pH range is optimal in terms of the purity of rhodium obtained from ANG in the subsequent stages of salt treatment, as well as saving ammonia and reagents required for processing mother liquors from ANG deposition.

 The lower PH limit provides an increase in the extraction of rhodium in ANH from 80.3 (experiment without neutralization) to more than 99.6% with a minimum consumption of ammonia for neutralization (Table 2).

 The increase in pH in the range from 1 to 3 - 5, as can be seen from the table. 2, leads to a decrease in the residual content of rhodium in the mother liquor of ANG, as well as to a certain increase in the content of ammonium chloride in the filtrate of the neutralized mother liquor PZA. The latter allows, together with a solution - an industrial product of refining palladium, to process a slightly larger amount of a solution - an industrial product of refining rhodium.

 The increase in PH in the range of 1 to 5 does not contribute to the deterioration of the quality of rhodium obtained from ANG.

 An increase in PH of more than 5 is undesirable, since residual platinum is converted into the form of amine complexes in the filtrate, which contributes to an increase in the platinum content in refined rhodium at the final stages of rhodium refining. In addition, the concentration of ammonium chloride in the filtrate after neutralization of the mother liquor of PZA does not increase, therefore, ammonia is consumed uselessly.

 If it is necessary to increase the concentration of ammonium chloride in the filtrate of the neutralized solution, it can be evaporated. The most appropriate multiplicity of reducing the volume of the solution during evaporation is in the range of 1.5-2. As shown by production experiments using evaporated filtrate for precipitation of ANG, evaporation, cooling, and subsequent filtration are accompanied by the precipitation of an additional amount of platinum and palladium, which improves the quality of rhodium and at the same time improves the recovery of other PGMs to the corresponding commercial products.

 Examples of the method.

 Examples 1. As the starting products, solutions of tetramine palladochloride and a solution of nitro complexes containing sodium hexanitro-rhodiate were typical for refining production of PGM. The pH of the tetramine palladochloride solution was about 9.0; the pH of the solution containing sodium hexanitro-rhodiate was about 5.0. The chemical composition of the solutions taken is given in table 1.

 The tetramine palladochloride solution was treated (titrated) with hydrochloric acid to control the completeness of the deposition of palladosmin and the completeness of the transfer of non-precious elements into the mother liquor. The completeness of the deposition of PZA was judged by the cessation of precipitation. The completeness of the transfer to the mother liquor of base elements was determined according to x-ray spectral analysis. The completeness of the deposition with a minimum content in the PZA of impurities of base elements was recorded upon reaching PH -0.35. Further rushing of hydrochloric acid did not increase the amount of PZA precipitate and did not increase the content of base elements in the PZA mother liquor. PZA precipitate was separated from the mother liquor by filtration. The mother liquor was cooled to room temperature and the precipitated suspension of palladosammine was again filtered.

The cooled filtrate of the PZA stock solution had a density of 1.061 g / cm ³ , pH -0.35 and contained, in g / l: 130.8 NH ₄ Cl; 43.5 free HCl; 0.108 Pt; 0.448 Pd; 0.010 Rh; 0.004 Ru; traces of Ir, Au and Ag; 0.267 Cu; 0.246 Se; 0.027 Sb; 0.008 Ni.

Equal volumes of the acidic mother liquor (filtrate) were neutralized with ammonia water until various pH values were established in the range from 1 to 7. (Ammonia water had a density of 0–905 g / cm ³ and contained 231.9 g / l NH ₃ ). Received 5 samples of solutions containing ammonium chloride having a pH of from 1 to 7.

 In the process of neutralizing the acidic mother liquor in a small amount (in the form of a suspension), precipitates formed, the content of mixed salts of platinum and palladium. The neutralized solutions were again filtered from the precipitated suspension.

 All filtrates of neutralized PZA mother liquors contained approximately equal contents, in g / l: 0.087 Pt; 0.251 Pd; 0.007 Rh; 0.003 Ru; traces of Ir, Au and Ag; 0.242 Cu; 0.240 Se; 0.023 Sb; 0.008 Ni.

 Obtaining after neutralization, samples of PZA mother liquors with various ph values in the range from 1 to 7, as well as directly the initial acidic mother liquor having PH -0.35, were used as solutions of ammonium chloride for precipitation of ammonium sodium hexanitrite (ANH) of rhodium from a nitrated solution PGM, the composition of which is given in table. one.

For this purpose, mother liquors from PZA were mixed with about five times the volume of a solution of PGM nitro complexes containing rhodium hexanitrite, the reaction masses were moved for 1 h, after which the released salts were filtered off. The results of the analysis showed that in all cases, the precipitate was represented by the salt (NH ₄ ) ₂ NaRh (NO ₂ ) ₆ - ANG of rhodium.

 The data on the residual content of rhodium in the mother liquors and its extraction into salt, as well as the total content of certain impurities in the rhodium ANG (in percent relative to the content of rhodium) are presented in table. 2. As can be seen from the data presented, the use of uterine solutions not acidic but pre-neutralized with ammonia water in the precipitation of ANG of rhodium can increase the extraction of rhodium into salt from 80.3 to 99.7–99.8%. At the same time, the content of impurities in the rhodium ANG decreases from 16.28 to 12.68 - 14.72% (by 1.5 - 3.6%).

 The deposition rates of rhodium in ANG from the nitrated solution with filtrates obtained from the mother liquor from PZA were no worse than when using pure commercial ammonium chloride.

 The obtained ANG samples were processed to produce rhodium using a known technology, including dissolution in hydrochloric acid, extraction purification of the chloride solution and electrolysis. The purity of the obtained metal required by GOST-12342-81 was achieved when using neutralized uterine PZA samples ranging from 1 to 5 as ammonium chloride for precipitation of ANG. A sample of rhodium obtained by using PZA stock solution in the deposition of ANG as ammonium chloride having PH 7, characterized by a high content of platinum.

 The mother liquors from the deposition of ANG were processed according to the existing technology, including the process of cementing PGM with iron, while no complications of the process were noted.

 Example 2. During production tests, which lasted from May to December 1997, the mother liquors from precipitation of PZA from solutions of tetramine palladochloride were neutralized with ammonia water until pH 4.5-5 was established, and the released salts were filtered off.

 Salts weighing 75.3 kg with a content of 3.61% platinum and 23.87% palladium were processed using the existing technology in the refining workshop of platinum and palladium to produce refined metals.

The filtrates of the neutralized solutions had a density of 1.02 to 1.06 g / cm ³ and contained ammonium chloride from 50 to 165 g / l. These filtrates were evaporated in a vacuum evaporation apparatus to obtain the density of the evaporated solution of 1.075 - 1.085 g / cm ³ . One stripped off solution was defended in a collecting tank. The settled evaporated solution was used to precipitate ANG from nitrite solutions containing rhodium hexanitrite.

 During the tests, a sediment weighing about 20 kg was formed at the bottom of the collection tank. Sludge containing,%: platinum - 7.8 and palladium - 22.0 transferred to the refining workshop of platinum and palladium.

 In the course of production testing of joint processing of solutions - intermediate products of refining palladium and rhodium, 14 samples of rhodium were obtained. All 14 samples met the requirements of GOST 12342-81 (powder-bound rhodium).

As can be seen from example 2, the proposed method for the joint processing of solutions-intermediate products of the refining of palladium and rhodium allows:
avoid the consumption of purchased ammonium chloride in the concentration of rhodium in the ANG,
reduce the yield of stock solutions of refining production,
return to the refining cycles of platinum and palladium according to the reduced scheme an additional amount of these metals.

 Replacing purchased ammonium chloride upon receipt of rhodium with a refining solution of industrial product does not impair the quality of marketable products.

Claims (2)

 1. A method of processing solutions of industrial products of the refining production of platinum group metals, including the precipitation of palladium from a solution of tetraammine palladochloride in the form of palladosammine (PZA) with hydrochloric acid, the precipitation of rhodium from a solution of its sodium hexanitrite with ammonium chloride in the form of ammonium-sodium precipitate of rhodium nitrite (ANN) PZA and ANG of rhodium by filtration, additional extraction of precious metals from mother liquors of refining of PGM by cementation methods with base elements, characterized in that the uterine thief from deposition palladozammine neutralized with ammonia until a pH in the range from 1 to 5, the neutralized solution is filtered off from the precipitate, and used as ammonium chloride during the deposition of rhodium ENG.  2. The method according to p. 1, characterized in that the neutralized mother liquor from the deposition of PZA before use is evaporated, the evaporated solution is cooled and an additional precipitate is separated.

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