Recycling of silver-plated brass for production of high purity copper and ultrafine silver powder for electric contacts

Abstract

The paper presents an improved process for recycling of silver-plate brass housing. Silver and copper are recovered with a purity of 99.99 % and 99.90 %, respectively, with the aim of obtaining materials of higher value using additional procedures based on the same process and equipment. The novel approach with subsequent electrorefining yields copper of 99.99 % purity with BS EN 1978:1998 (Cu-CATH-1) quality and is referred to as LME grade A. Additional processing of silver results in superfine, micro-sized Ag powder with partie size from 0.14 to 1.13 mu m and purity of 99.999 %. Copper electrorefining tests were performed using 1.50 dm(3) of synthetic electrolyte in a 2 dm(3) electrolytic cell. Effects of current density and electrolyte composition were investigated. Optimal current density for the first and second refining was 120 A/m(2) and 200 A/m(2), respectively. Additional refining of silver was performed by chemical reduction from an aqueous solution. Optimal results were obtained with ascorbic acid as a reduction agent in concentration of 0.1 mol/dm(3) and polyvinylpyrrolidon as a protective agent in concentration of 2 % by mass. The investigation results could be adopted into production.