Biological pre-oxidation to enhance gold and silver recovery from refractory pyritic ores and concentrates

CIM Bulletin, Vol. 76, No. 857, 1983

R.W. LAWRENCE and A. BRUYNESTEYN, Division of Extractive Metallurgy, B.C. Research, Vancouver, B.C.

Pre-oxidation of refractory pyritic concentrates by biological leaching to enhance the recovery of gold and silver in cyanida-tion has been investigated. The results of laboratory tests on three concentrates are presented. In all cases substantial increases in precious metal recoveries were obtained following the pre-treatment. For one concentrate, gold recovery of 81% was achieved following an 87% oxidation of pyrite, compared with 24% recovery by direct cyanidation of non-oxidized concentrate. Gold and silver recoveries from the other concentrates were increased from the range 60-78% to over 90% and from 80-86% to over 98% respectively. Operating parameters are discussed and methods of maintaining high oxidation rates are evaluated. Methods of employing this pre-oxidation technique in commercial practice are described.

Keywords: Gold extraction, Leaching, Biological leaching, Cyanide leaching, Gold recovery, Silver extraction, Silver recovery, Refractory ores, Porgera concentrate, Cinola concentrate, Ore mineralogy.