EJMP&EP





Thermophilic Bioheap Leaching of Chalcopyrite Concentrates

T.J. Harvey1*, N. Holder2, T. Stanek2

1 GeoBiotics, LLC, 12211 W. Alameda Pkwy, Suite 101, Lakewood, CO, 80228, USA
2 Lakefield Research Africa (Pty) Ltd, 58 Melvill Street, Booysens, Gauteng, 2091, South Africa

Received 13 June 2002; accepted 15 October 2002



ABSTRACT

The 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.


Keywords: Bacteria; Biooxidation; Chalcopyrite; Hydrometallurgy; Thermophile



* Corresponding Author
   E-mail : tharvey@geobiotics.com