Thermophilic Bioheap Leaching of
extraction of copper from chalcopyrite has for centuries been limited to pyrometallurgical
methods. Smelting of chalcopyrite is an efficient process but costly both in terms of
capital investment, operating costs and environmental compliance. Biological extraction
appeared as an appealing alternative. Unfortunately, traditional mesophilic biological
extraction methods have met with little success. The chalcopyrite quickly becomes
passivated and unacceptable copper extractions are achieved. It was not until the adoption
of thermophilic systems that the biological leaching of chalcopyrite became a reality.
Several questions remain as to the applicability of the thermophilic system for
chalcopyrite; can the system operate auto-thermally; can high extraction rates be
achieved; is the process sensitive to mineralogy or grade; and can the precious metals be
recovered? GeoBiotics, LLC has embarked on an extensive program to develop the GEOCOAT®
bioleaching system to chalcopyrite ores. This program encompasses mathematical heap
modeling, laboratory amenability and column tests, and large scale field trials. The
GEOCOAT® process involves the coating of concentrates onto a suitable
substrate, usually barren rock, then stacking the coated material in a conventional heap
fashion. The heap is irrigated with acidic solutions containing iron and nutrients while
low pressure ambient air is applied at the heap base. To-date, copper extractions in
excess of 97% have been achieved in approximately 140 days. Excellent gold extractions
have been achieved from the biooxidation residue by cyanidation. Modeling indicates that
obtaining thermophilic temperatures within the GEOCOAT® heap is not a problem.
Development is continuing, focusing on the heap design parameters and additional copper
concentrates including enargite. Plans are now underway for the first large scale field
test in the fall of 2002.