LEACHING OF A SILVER BEARING SULFIDE BY-PRODUCT WITH CYANIDE, THIOUREA AND CHLORIDE SOLUTIONS

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 Fe3+ 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 Fe3+. Operating under [Cl-]greater-than-or-equal-to3 M at 80-90-degrees-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.