Kinetic and electrochemical study of silver leaching in thiosulfate solutions using a closed vessel system

Abstract

Recently, many studies have focused on thiosulfate as one of the promising alternatives to cyanide for gold leaching. However, few studies have evaluated the leaching of silver in thiosulfate solutions. In this study, the leaching of pure silver (99.99% Ag) in thiosulfate solutions containing copper and ammonia is investigated. The effects of various parameters on the silver leaching kinetics were evaluated using a rotating disc technique in open and closed vessels. It was found that the leaching rate of silver in the closed vessel was greater than that obtained in the open vessel. Silver leaching rates were affected positively by increasing ammonia, thiosulfate, and copper(II) concentrations. An electrochemical study showed that increasing thiosulfate and ammonia concentrations has positive effects on the anodic dissolution of silver, however, the presence of thiourea has a negative effect on the anodic dissolution of silver. Finally the study showed that the optimum leaching conditions for silver is: 10 mM Cu(II), 0.8 M NH3 , 0.2 M (S2O3)2-, 30 ºC, 300 rpm, and pH =11.5.