Bio-oxidation of a refractory gold bearing high arsenic sulphide concentrate: A pilot study

Abstract

A modular mobile bioleach pilot plant has been designed and constructed by Coastech Research Inc. The pilot plant was designed to be transported on two flatbed trucks to any location in North America for on-site piloting. The first bioleach demonstration pilot study was completed on a refractory gold bearing high arsenic (7.5% As) sulphide (28.9% S) flotation concentrate. A production capacity of up to 562 kg per day at a feed solids concentration of approximately 14% (w/w) solids and overall retention time of 115 h was achieved under steady operating conditions. Sulphide oxidation exceeded 75% while almost complete arsenic solubilization was observed for the final bioleached product. Oxygen and carbon dioxide uptake rates were obtained from off gas analyses. Oxygen uptake rates as high as 0.99 kg h−1 m−3 were observed. A critical dissolved oxygen concentration, to maintain chemical oxidation, within the range of 0.7–1.1 ppm was observed. Carbon dioxide uptake ratcs were decreased at dissolved oxygen concentrations below approximately 0.7–0.5 ppm. Gold extraction was enhanced from approximately 5% for the pretreated flotation concentrate, to in excess of 90% for the final bioleached product. A worker environment monitoring program was undertaken during the pilot plant operation. All samples taken for air-borne and urinary monitoring were below their respective time weighted average exposure limits.