A novel anaerobic bioprocess for liberating precious metals like gold and silver from sulfidic ores. As near-surface, oxidized ore reserves are depleted, gold producers are increasingly faced with the challenge of extracting gold and other metal values from sulfidic ores that are refractory to conventional processing techniques. At present, when the demand is high for more cost-effective and environmentally-friendly ore processing options, bioprocessing is considered impractical for large-scale application for three reasons: (1) slurry cooling requirements on the order of megawatts, (2) difficulties in delivering oxygen into slurries at very high rates, and (3) excessive neutralization reagent costs and sludge production. This research has employed the tools of the bioprocess engineering discipline (including analysis of reaction energetics, recognition of microbial capabilities and a reactor engineering approach) to overcome these issues.
The results of the proof-of-concept experiment conducted during this project indicate that the proposed process is technically feasible. Metal sulfide dissolution rates achieved by the anaerobic process were equal to or greater than those achieved by the conventional, aerobic (control) process. The mean extent of gold liberation was greater in the anaerobic process during one (the final) run. In two other runs, more gold was liberated in the aerobic control, but not significantly more, statistically. Preliminary cost estimates indicate that the cost of the proposed anaerobic process is equal to that of the conventional aerobic process within the accuracy of the estimates. The proposed process has other advantages in that it has the potential to substantially reduce the environmental impacts of mining activities.
Examples of Applications and Markets:
International gold producers spend over $10 billion annually to process gold ores. Recent interest in biotechnologies has been sparked by a change in the mineralogy of the ores being processed and severe cost and environmental pressures. This innovative anaerobic bioprocess for liberating gold and silver from sulfidic ores presents an appealing alternative.
Our studies in Phase I revealed no theoretical or practical reasons why an optimized YES process cannot achieve the efficiency and efficacy on par with the conventional, aerobic process. Additional R&D funding is being sought to expand research on specific steps critical to the process.
"Method and Apparatus for Extracting Precious Metals from Their Ores and the Product Thereof,"
"Biocatalyzed Partial Demineralization of Acidic Metal Sulfate Solutions," U.S. Patent No. 5,076,927, issued December 31, 1991.
"Biocatalyzed Anaerobic Oxidation of Metal Sulfides for Recovery of Metal Values,"
Phase I Final Report -- Anaerobic Bioprocess for Liberating Gold and Silver from Sulfidic Ores (research sponsored by U.S. Department of Agriculture), December 1997, pp.27 plus appendices.