PROCESS OF EXTRACTING GOLD AND SILVER FROM ORES AND MINING BY-PRODUCTS

Abstract

The invention relates to a process for the extraction of gold and silver from ores and mining by-products. The process according to invention consists in treating ores and mining residues having a content of 0.5 . . . 12 ppm Au with a solution of ammonium thiosulphate, recycled at a temperature of 15-25 C.; the filtrate resulting after solubilization is subjected to an electrolytic extraction with high-alloy electrodes with a current density of 200 . . . 250 A/m.sup.2, until the electrolyte reach a concentration of 5-15 ppm Au, 1-100 ppm Ag and 0.1-1.0 g/1 Cu; afterwards, the separated cement is filtered off and dissolved in aqueous ammonia, dried at a temperature of 105 C. and melted at a temperature of 1200 C., resulting a Au-Ag alloy, which is processed by electrochemical and thermal refining operations, from which there are obtained Au and Ag of high purity.

Claims

1. Process of extracting gold and silver from gold ores and mining by-products, which comprises treating gold ores, pyrite concentrates or mining by-products consisting of mining and metallurgical residues, characterized in that: solubilizing the raw material in a solution of ammonium thiosulphate, recycled from the process, with a content of 10 to 25 g/l (NH.sub.4).sub.2S.sub.2O.sub.3; 0.1 to 1.0 g/l Cu; 0.3 to 0.4 g/l NH.sub.4OH at a solid:liquid ratio of 1:1 . . . 1:1.5, at a temperature of 15-25 C. for 2-4 hours; the filtrate obtained after dissolution, with a content of 10 to 25 g/l (NH.sub.4).sub.2S.sub.2O.sub.3, 6-20 ppm Au, 2-150 ppm Ag, 0.12-1,2 g/l Cu, 0.3-0.4 g/l NH.sub.4OH, is subjected to an electrolysis with high-alloy steel electrodes with a current density of 200-250 A/m.sup.2, until the electrolyte has a concentration of 5-15 ppm Au, 1-100 ppm Ag and 0.1-1.0 g/l Cu; the cementum separated in electrolysis cells, after a total of 20 cycles, is filtered off and dissolved in aqueous ammonia having a concentration of 20% NH 3 at a solid:liquid ratio of 1:5 1:10 for 3-5 hours; after which it is filtered, washed with water, dried at a temperature of 105 C. and melted in a alkaline-reducing medium at a temperature of 1,200 C., resulting a AuAg alloy, from which, by electrochemical and thermal refining, there are obtained gold and silver 99.9%, and the filtered solution copper ammineis recycled to process, in order to correct the copper content of the electrolyte used in the leaching of raw materials.

Description

EXAMPLE 1

[0014] In a reactor made of alloy steel or enamelled cast iron with a capacity of 2 m.sup.3, equipped with a stirring system, are introduced 1.5 m.sup.3 of solution from the alkaline electrolysis operation, comprising: 10 to 25 g/l (NH.sub.4).sub.2S.sub.2O.sub.3; 13-15 ppm Au; 50-60 ppm Ag; 0.1 to 0.12 g/l Cu, adjusted to 0.12-0.15 g/l Cu, by addition of copper ammine, derived from the dissolution of the CuAuAg cementum in aqueous ammonia at pH 10-11 and 1,500 kg of silica residue resulting from the flotation of complex ores, containing 0.7 ppm Au and 10.5 ppm Ag. The suspension was stirred for 4 hours with air bubbling 30 m.sup.3/h, and filtered on a vacuum rotary drum filter with a filter area of 1 m.sup.2. The slurry resulting after filteringa quartz residueis washed with 100-150 litres of water, is free of impurities, has a moisture content of 8-10% and can be used as a construction filler material. The filtered solution with a volume of 1.5-1.6 m.sup.3, which contains 10 to 25 g/l (NH.sub.4).sub.2S.sub.2O.sub.3, 13.2-15.5 ppm Au, 51-65 ppm Ag and 0.12 to 0.15 g/l Cu (pH 10-11) is subjected to electrolysis with anodes made of high-alloy steel, the electric current density of 200-250 A/m.sup.2. The electrolytical cell, having a capacity of 2 m.sup.3, is equipped with two electrodes of equal surfaces of 1 m.sup.2. The electrolyte is internally recycled at a rate of 2 m.sup.3/h. The operation takes about 2 hours and is considered finished when the electrolyte that leaves the cell contains 13.0 to 15.0 ppm Au, 50-60 ppm Ag and 0.10 to 0.12 g/l Cu. After a total of about 20 cycles of electrolysis, the cementum separated in the conical part of the cell, in an amount of 1.0-1.5 kg, with a content of 0.9 to 1.0% Au, 17-19% Ag and 35-45% Cu, is filtered and washed with water. The leaching of the copper cementum in the filtrate is carried out in a reactor made of enamelled iron of 100 litres, ammonia water having a concentration of 20% NH.sup.3 at a solid:liquid ratio of 1:3 . . . 1:5, under stirring, with the absorption of ammonia removed from the reactor into a tower with packing, sprayed with water. The operation takes 3-5 hours.The suspension is filtered on a nuce filter under vacuum. Decoppered cement, after washing with water, with a content of maximum 5% Cu, 3-3.5% Au and 50-60% Ag is dried, mixed with sodium carbonate and carbon at a ratio of 1:3:0.5 is melted in a graphite crucible, at a temperature of 1200 C. The AuAg alloythe dor alloyis cast into anodes and subjected to known-per-se operations of electrochemical and thermal refining, in order to obtain pure gold and silver. The slag obtained by smelting cementum is ground and recycled to the leaching operation of the raw material. The overall yield of the operation oremetal is 70% to 86% for Au and Ag.

EXAMPLE 2

[0015] Under similar operations as in Example 1, with the difference that the raw material is a pyrite concentrate refractive to the dissolution in an alkaline cyanide solution, containing 12 ppm Au, 50 ppm Ag, and after dissolving results a pyrite with 0.95 ppm Au and 2.5 ppm Ag. The overall yield of the operation pyrite concentratesmetal is 86.2% to 89.7% for Au and Ag.