Gold recovery from a refractory pyrrhotite ore by biooxidation

The aim of the present investigation was to study the biooxidation of a ref ractory gold-bearing pyrrhotite, in order to increase the gold recovery dur ing the subsequent conventional cyanidation. Bacterial cultures utilised in the biological test consisted predominantly of Thiobacillus genus. Tests were conducted at laboratory scale. The gold c ontent of the ore sample, coming from Bolivia, was of 10 g t(-1) Au. After 24 h leaching time by direct cyanidation, low gold recovery was obtai ned (< 20% Au), with a high reagent consumption. On the other hand, a high gold recovery was achieved for the biooxidated samples: after 24 h cyanidat ion gold dissolution reached about 91% Au. Experimental results have shown the technical feasibility of the biooxidati ve pretreatment prior to conventional leaching and a complete circuit of tr eatment, on laboratory scale, has been developed considering also the subse quent gold recovery by carbon adsorption/desorption and electrowinning. A gold extraction yield of about 86% was determined in the whole process fo r gold extraction from pyrrhotite (biooxidation, solid-liquid separation, c yanidation, adsorption, desorption, electrowinning). (C) 2000 Elsevier Scie nce B.V. All rights reserved.