Gold and silver extraction technology

Abstract

The present invention relates to a process for chemical extraction of gold and silver from low grade and refractory pyritic concentrates containing minimum 1 ppm Au, by their leaching in enameled cast iron reactors, steel plated lead or plastic coated steel, at room temperature, in ammoniac solutions (pH 8-10) of sodium thiosulfate (50-60 g/l Na2S2O3. 5 H2O) with a divalent copper salt as catalyst (3-4 g/l Cu). The suspension resulting after 2-4 hours of reaction is filtered. The thiosulfate solution containing minimum 5 mg/l undergoes an electrolysis process with insoluble anodes. Copper, gold and silver is deposited in the cell as a sludge, and the electrolyte having a maximum content of Au of 1 mg/l, is recycled to the leaching operation of raw material, after correction of copper content and alkalinity to the baseline values. The copper, gold and silver deposit, separated as a sludge, is purified by leaching copper in a solution of 30-40% sulphuric acid at a solid:liquid ratio of 1:5-1:10, at a temperature of 85-90° C. for 2-4 hours under air bubbling. The suspension is filtered. The copper leached as CuSO4.5H2O returns to the extraction process of gold and silver.

Dependencies are inferred from the claim text.