Leaching of a silver bearing sulphide by-product with cyanide, thiourea and chloride solutions

Abstract

The aim of this research was to increase the value of sulphide tailings assaying 1000-1500 g/ton Ag per tonne and high arsenic (about 13%) content. The sulphides were characterized and it was verified that silver occurs both as mathildite, AgBiS2, and in solid solution in galena. Three alternative routes were assessed: cyanidation, thiourea leaching and chloride leaching. The cyanidation route showed that there was a high consumption of cyanide and led to the formation of an insoluble compound of silver thiocyanate. The leaching with thiourea was achieved without the introduction of Fe 3+ but it is not an economically viable route. Chloride leaching of the product in its original particle grain size showed very good extraction even without addition of Fe 3+. Operating under [Cl-_.3 M at 80-90°C for at least 3 h it was possible to dissolve 60-80% of the total silver, and higher recoveries of lead and bismuth were also achieved.