RU2351667C1 - Treatment method of zinc-bearing golden-silver cyanic sediments - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: invention is related to noble metals metallurgy and can be used for technology of desilverisation and gold extraction from zinc-bearing golden-silver cyanic sediments with increased content of silver. Initial zinc-bearing golden-silver cyanic sediment is leached, at first, in nitric acid solution and then into received pulp excluding filtration it is added caustic soda solution till achieving the concentration NaOH, equal to 100-140 g/l. After it alkaline solution is separated from non-solved sediment. The latter is washed by alkaline solution, dried, molten with fluxes on golden-silver alloy. Received alloy is settled, slag is separated from silver gold-bearing alloy, which is directed to silver refining by means of electrolysis in nitro-acid electrolyte. Electrolysis products are refined cathodic silver and golden sludge, which is refined by well-known methods. ^ EFFECT: removing of detrimental impurities, essentially, zinc, selenium and tellurium made of initial cyanic sediment. ^ 1 ex

Description

The invention relates to the metallurgy of noble metals (BM) and can be used in the technology of extracting silver and gold from zinc-containing gold-silver cyanide deposits with a high content of silver.

One of the most common methods for extracting silver and gold from ore is cyanidation.

The essence of this process is the leaching of precious metals using cyanide salts of alkali or alkaline earth metals in the presence of atmospheric oxygen. The silver and gold that transferred to the solution are then precipitated with metal zinc cementation. The resulting zinc-containing gold-silver cyanide deposits after separation from cyanide solutions are processed to extract silver and gold.

As a result of the deposition of precious metals by zinc dust, cyanide precipitates of a very complex material composition are obtained. Along with silver and gold, they contain an excess of metallic zinc, metallic lead, zinc hydroxide and carbonate, simple zinc cyanide, calcium carbonate and sulfate, compounds of copper, iron, arsenic, selenium, tellurium. In addition, oxides of silicon, calcium, aluminum, etc. are present in the sediments [I.N. Maslenitsky, L.V. Chugaev, V.F. Borbat and others. Metallurgy of noble metals. - 2nd ed., - M .: Metallurgy, 1987, p.180].

The compositions of cyanide sediments obtained at various gold-mining plants vary significantly, which is associated both with different types of mineral raw materials and with the peculiarities of the cyanization and cementation technologies used.

So, cyanide zinc-containing precipitates obtained at gold mining enterprises of the Magadan Region are characterized by extremely high silver (30-80%), relatively low gold (0.2-4%) and zinc (5-15%), and selenium and tellurium (up to 2%), lead (up to 30%), copper (0.1-5.0%), oxides of silicon, calcium, aluminum.

The choice of methods for processing cyanide sediments is determined by the composition of the sediments, their amount and requirements for the degree of extraction of precious metals.

A known method of processing gold-silver cyanide sediments, which consists in the direct smelting of sediments in a crucible with fluxes without any preliminary treatment. Soda, borax, quartz sand and fluorspar are used as fluxes. In direct smelting of zinc-containing cyanide sediments, the resulting slag contains oxides that strongly corrode the crucible. During smelting, a significant amount of zinc oxides, cyanides and other substances is released. As a result of melting, a highly contaminated low-grade gold-silver alloy is often obtained. The slag obtained during this operation contains a significant amount of precious metals and must be specially treated. [I.N. Plaksin. Metallurgy of precious metals. Textbook for technical colleges. - M., Metallurgizdat, 1943, p. 297-304].

This method is rarely used and only for the processing of very pure sediments that do not contain harmful impurities. In particular, this method cannot be used for processing cyanide sediments with a high content of silver contaminated with selenium and tellurium obtained at enterprises of the Magadan region, since the presence of these impurities in the gold-silver alloy complicates its subsequent refining and makes it difficult to use electrolysis in nitric acid for this media (chalcogens contained in the anode alloy pollute cathode silver).

The most widely used method of processing zinc-containing gold-silver cyanide sediments, which consists in acid treatment of the precipitate, separation of the solution from insoluble precipitate, washing the precipitate with water, drying and subsequent melting with fluxes in order to obtain a silver-silver alloy suitable for further refining [I.N. Maslenitsky, L.V. Chugaev, V.F. Borbat et al. Metallurgy of precious metals. - 2nd ed., - M.: Metallurgy, 1987, S. 180-188 and S. 315-327].

This method is the closest in technical essence to the claimed method and adopted as a prototype.

According to the prototype method, the initial precipitate is leached with a (10-15)% solution of sulfuric acid in order to remove the bulk of zinc and other acid-soluble compounds into the solution. At the end of leaching, the solution is separated by filtration from the insoluble precipitate, washed with water, dried and melted with fluxes onto a silver-silver alloy. The fluxes used are soda, borax, quartz sand, fluorspar.

The purpose of the smelting is an additional separation of base substances into the slag and obtaining a gold-silver alloy suitable for subsequent refining. For melting can be used furnaces of various designs. Melting lead to the complete fluidity of the slag. At the end of the smelting, the melt is settled and the resulting slag is separated from the gold-silver alloy. Upon receipt of a sufficiently rich gold-silver alloy (950-980 samples), it is sent for refining (including by electrolysis). If the melted metal is not clean enough, then it is subjected to re-melting with the aim of refining.

The main disadvantages of the prototype method, when it is used for the processing of zinc-containing gold-silver cyanide sediments with a high content of silver (including precipitates obtained at enterprises of the Magadan region), include:

- evolution of explosive hydrogen during the interaction of zinc with sulfuric acid;

- low extraction of selenium and tellurium into the sulfuric acid solution from silver enriched precipitates, which during subsequent melting leads to the production of a silver gold-containing alloy contaminated with chalcogenes and does not allow its refining in one stage of electrolysis in nitric acid electrolyte without the use of additional purification operations;

- the formation of difficult to filter pulp, which requires the use of sophisticated filtering equipment.

The technical result, which is achieved by the proposed method for processing zinc-containing gold-silver cyanide sediments with a high silver content, consists in using a combination of such hydrometallurgical processing methods that allow purifying the initial precipitate from harmful impurities (mainly from zinc and chalcogenes) and, at the same time, do not have the above disadvantages inherent in the prototype method.

The objective of the invention is directed to obtaining from the initial cyanide precipitates such a product which, after washing, drying, smelting with fluxes and separation from slag, would be a silver gold-containing alloy suitable for refining (including electrolytic production of refined silver in nitric acid electrolyte).

The achievement of the technical result is ensured by the fact that the initial zinc-containing gold-silver cyanide precipitate is leached first in a solution of nitric acid, then a solution of caustic soda is added to the resulting pulp (without filtering it), and only then the alkaline solution is separated from the insoluble precipitate. The latter is washed with an alkaline solution, dried, melted with fluxes on a silver-silver alloy. Melting lead to the complete fluidity of the slag. The obtained melt is settled, the slag is separated from the silver gold-containing alloy, which is sent to silver refining by electrolysis in a nitric acid electrolyte.

The essence of the proposed method is as follows. When the starting product is leached in nitric acid, zinc, most of the acid-soluble impurities, and also silver pass into the solution (the formation of an explosive air-hydrogen mixture in this process is excluded). Gold, silicon and aluminum oxides are concentrated in the insoluble residue. The resulting pulp is then, without filtering, treated with a solution of caustic soda. In an alkaline environment, silver nitrate turns into a practically insoluble oxide and precipitates. Impurities of copper and lead are also precipitated in the form of hydroxides. Selenium and tellurium in an alkaline medium form soluble acids (H ₂ SeO ₃ , H ₂ TeO ₃ ) and remain in solution. Zinc is an amphoteric metal. When alkalizing nitrate solutions to pH = (8-10), zinc passes into the precipitate in the form of hydroxide. However, in an excess of alkali, the zinc hydroxide precipitate is dissolved with the formation of sodium zincate (Na ₂ ZnO ₂ · 4H ₂ O). It was experimentally established that the complete dissolution of Zn (OH) _{2 is} achieved when the NaOH concentration in the pulp is more than 100 g / l. It is not advisable to raise the concentration of sodium hydroxide above 140 g / l, since the completeness of the dissolution of zinc compounds does not increase, and the costs increase significantly.

As a result of such a combination of chemical transformations, a pulp is formed, the solid basis of which is well-filtered silver oxide, gold, silica. Subsequent filtration and washing of the precipitate make it possible to achieve the desired degree of separation of the zinc, selenium, and tellurium transferred to the solution from the insoluble precipitate. The residual content of zinc and chalcogenes in the insoluble precipitate is small and does not impair the performance of subsequent smelting.

The resulting insoluble precipitate is dried to remove free moisture and then melted with fluxes in electric or fuel furnaces. In the process of melting, fluxes interact with silica and other components of the mixture, forming a liquid-mobile slag. Silver oxide is reduced due to thermal dissociation and, together with gold, forms a silver gold-containing alloy, which, due to insolubility in slag and higher density, settles to the bottom of the melting furnace. After settling the melt and separating the slag from the silver gold-containing alloy, the latter is subjected to refining.

Due to the high silver content and small amounts of harmful impurities (selenium and tellurium), the alloy is refined by electrolysis of silver in nitric acid solutions. The electrolysis products are refined cathode silver and gold sludge, which is refined by known methods.

Example

400 g of the initial product, a zinc-containing gold-silver cyanide precipitate of one of the gold-mining factories in the Magadan region, was placed in a glass. The initial product (humidity - 5%) had the following content of the analyzed elements,%: gold - 0.25; silver - 78.1; zinc - 6.0; selenium - 0.74; tellurium - 0.2.

400 ml of water was added to the initial product, nitric acid was added to the resulting pulp to pH = 0.5-1.0. The initial product was leached in a nitric acid solution, for which the resulting pulp was stirred at a temperature of 70 ° C for 30 minutes.

After that, a solution of caustic soda in an amount of 500 ml (solution density - 1.46 g / cm ³ ) was added to the pulp and kept with stirring for 60 minutes. It was determined by titration that the concentration of free NaOH in solution was 120 g / l. Then, the alkaline solution was separated by filtration from the insoluble precipitate. The volume of alkaline solution was 1000 ml at the following concentration of the analyzed elements, g / l: Zn - 16.1; Se - 2.14; Those are 0, 6; Ag - 0.003; Au - less than 0.002 g / l.

The insoluble precipitate was washed on the filter with a NaOH solution, as a result of which 600 ml of wash water were obtained, which contained, g / l: Zn - 7.9; Se - 1.03; Those are 0.2; Ag - no; Au - no, and also - 593 g of wet insoluble sediment. The latter was placed in a drying oven and dried for 4 hours at a temperature of 110 ° C. The result was 374.9 g of dry insoluble precipitate, which according to the results of the analysis contained,%: Ag - 79.16; Au 0.25; Zn - 0.51; Se - 0.013; Those are not.

The insoluble precipitate obtained after drying was melted with fluxes in order to obtain a silver gold-containing alloy. For this, 360.0 g of dry insoluble precipitate (the rest of the precipitate was used up for analysis) was mixed with 30.0 g of quicklime (CaO) and 60.0 g of crushed silicate glass. All components of the charge were thoroughly mixed and placed in a chamotte melting crucible, which was loaded into a resistance shaft furnace. After isothermal aging in a furnace at a temperature of 1250 ° C for 60 minutes, the melt crucible was unloaded from the furnace and allowed to settle and cool to room temperature. Then the melting products were extracted from the crucible, the slag was separated from the silver gold-containing alloy at the natural phase boundary. 90.5 g of slag and 287.04 g of a silver gold-containing alloy were obtained. According to the results of the analysis, the alloy contained,%: Ag - 98.80; Au - 0.31; Zn - 0.0020; Se - 0.0032; Those are not.

Anodes were made from the obtained alloy and silver was successfully refined by electrolysis in a nitric acid electrolyte. As a result, cathode refined silver was obtained that corresponds in chemical composition to the requirements of GOST 28595-90, and gold slurry, which can be refined by known methods.

Claims (1)

A method for processing zinc-containing gold-silver cyanide sediments, including leaching the initial product in an acid solution, separating the solution from an insoluble precipitate, washing the insoluble precipitate, drying and melting it with fluxes, settling the melt, separating the resulting slag from a silver gold-containing alloy and refining the latter with electrolysis in an electrolyte, characterized in that nitric acid is used as the acid for leaching the starting material into the pulp obtained Adds caustic soda NaOH solution to achieve a concentration of 100-140 g / l, and then carried out the separation by an alkali solution undissolved precipitate, which is subjected to washing, drying and melting with fluxes.