Electrochemical recovery of silver from cyanide leaching solutions

Abstract

In the hydrometallurgy industry cyanide solutions are the most common leaching baths used during the extraction of metals such as silver and gold. After extraction, the solution containing various cyanide species, and usually copper cyanide, has a higher concentration than the gold and silver complexes. Higher concentration of copper species may interfere during the selective recovery of precious metals. This work presents a study of the selective recovery of silver from leaching solutions mimicking those used in industry. Chemical speciation and cyclic voltammetry studies showed that copper reduction occurs at more negative potentials than silver in the cyanide leaching solutions. The cyclic voltammetry of cyanide solutions on a vitreous carbon electrode showed that copper cyanide ions modify the interface properties, lowering the overpotential required for silver reduction. A macroelectrolysis study of a simulated leaching solution (10−4 M Ag(I), 0.1 M Cu(I) in 0.5 M CN− at pH 10), was carried out in a filter press electrochemical reactor (ElectroCell AB) with a reticulated vitreous carbon electrode (RVC), nominally having 45 pores per inch and a flow rate of 5 cm3 s−1 at 25 °C. The study showed that the high copper concentration does not interfere in the selective deposition of silver.