Recovery of pure silver from spent silver electroplating solutions via electrochemical process and zinc cementation

Abstract

Recycling of spent silver electroplating solutions has been investigated via electrowinning and electrorefining in comparison to zinc cementation technique in this research. Two different compositions of transparent and dark waste solutions were used having the remaining silver contents of 17.71 g⸳L-1 and 33.36 g⸳L-1 respectively. The waste solutions were used as an electrolyte in the first step of electrowinning at low current density of 0.015 A⸳cm-2. It was found that increasing electrowinning time from 4 h to 24 h increased the recovery of silver cathode for both types of waste solutions. The optimum electrowinning time was higher than 8 h, giving the recovery of higher than 97.5% and 98.5% purity for 24 h electrowinning. Through the subsequent electrorefining, the electrowon silver cathode was set as the anode, while HNO3 + AgNO3 electrolyte containing high silver content of 120 g Ag/L was used. By controlling the potential at 0.8 V, silver crystal of high purity > 99.9% was obtained. The highest recovery was 99.11% when using silver cathode obtained from electrowinning of the transparent waste solution. Zinc cementation however led to loss of silver in the precipitate form on the zinc metal surface, giving only 86.16% recovery.