Some studies on the extraction of gold and silver from lead-zinc sulfide flotation tailings through non-cyanide leachants

Gold and silver extractions from a low-grade lead-zinc sulphide flotation tailings has been investigated; using thiourea and thiosulphate as the lixiviants. Since the precious metals were finely disseminated in the matrices of the sulphide minerals, bioleaching of the flotation tailings was also carried out prior to the thiourea leaching. Biological preoxidation has been found to be very effective in releasing these precious metals by dissolving, albeit in part, the base metal sulphides. Direct thiourea leaching has yielded gold and silver recoveries of 23% and 45% whereas thiourea leaching of the bacterial leach residues resulted in enhanced gold and silver recoveries of 92% and 78% respectively. Thiosulphate leaching of the tailings at 50-degrees-C resulted in the highest gold extraction of about 95%.