Preliminary studies on improving gold leaching efficiency of Wiluna biooxidized residue

In this thesis, the leaching characteristics of biooxidized residue from the Wiluna gold mine are studied. The Wiluna BIOX residue was leached in bottle roll tests conducted at varying pulp densities and cyanide concentrations with the aim of studying the real leach characteristics of gold from the residue and determining which conditions result in the most profitable extraction of gold. The leaching in test 4 was conducted at a pulp density of 30% solids with 20 g/L of activated carbon in the pulp at an initial sodium cyanide concentration of 1500 mg/L which was maintained at 1000 mg/L. The gold leaching efficiency was found to achieve a recovery of 91.1% after 48 hours and 92.3% after 72 hours in test 4 and 93.2% after 48 hours of leaching in test 9 with a NaCN consumption of 12.25 and 12.69 kg NaCN, respectively, per tonne of concentrate treated. If the results from the bottle roll tests could be reproduced in the Wiluna plant, a reduction in pulp density from 40% to 30% solids in the carbon-in-leach would translate into an increase in revenue from the recovery of an additional 4 400 oz. p.a. The highest leaching efficiency of gold (96.2%) was obtained in test 21, which was conducted at an initial sodium cyanide concentration of 2825 mg/L which was maintained at 1883 mg/L NaCN and conducted at a pulp density of 10% solids w/w. The results of the bottle roll tests also showed that cyanide consumption increases as the mass percentage of solids in the pulp is reduced. The tests also illustrated that improvements in recovery and the rate of leaching were achieved as the mass percentage of solids in the pulp was reduced. The residue was observed to contain fast leaching and slow leaching gold as is illustrated by the initial large increases in gold concentration in the leach liquors and from the results of test 12 in which gold leaching was occurring even after 72 hours of cyanide leaching. Key words: Gold, Cyanidation, Leaching, Biooxidation, Refractory, Pulp Rheology, Bottle Rol