Understanding the factors that drive and limit heap bioleaching

Heap bioleaching is a low cost process option for the extraction of base metals from sulphide minerals (such as chalcocite, chalcopyrite and sphalerite) and for the oxidation of refractory gold ores. Although simple in principle - ore is stacked on a pile, solution is sprinkled from the top and the pregnant solution is collected at the base for metal extraction - the underlying sub-processes in terms of macro and micro transport, mineral kinetics and bio-dynamics are extremely complex. There is large scope for improving the rates of extraction currently experienced in heap leach operations by developing fundamental insights about the process dynamics.

Research during my stay at the University of British Columbia (2000- 2002), and now at UCT, has followed a two-pronged approach. Experimental work is focussed on the characterisation of ores in terms of leaching kinetics, and micro-organisms in terms of their growth and oxidation behaviour as well as colonisation characteristics. Simultaneously, a comprehensive heap modelling tool, HeapSim, has been developed, which, in an ongoing collaboration with Prof. David Dixon at UBC, continues to evolve. Both research directions are currently sponsored through the AMIRA P768 series of projects.

Leach mechanisms at the particulate and aggregate scale

Leaching of whole ores and complex concentrates is strongly governed by the types, concentrations and location of the different mineral phases within the ore or concentrate particle under leach. A new research direction is focussed on developing quantitative links between the mineralogy, particle topology, particle size distribution and packing and key leaching reactions, which would allow a more systematic understanding of leaching behaviour of a given ore or concentrate sample.

Process hydrometallurgy

In more general terms my interests cover the entire field of process hydrometallurgy, i.e. leaching in general, solvent extraction and electro-winning, and the development of teaching modules around this. An emerging special interest here is process development with a view to finding novel ways of metal recovery from minerals, wastes and recycled consumer goods.

Current and past projects

Current postgraduate projects

Tunde Ojumu (PhD): Kinetics of ferrous iron oxidation by Leptospirillum ferriphillum under conditions typical of heap bioleach environments

Thierry Kamunga Kazadi (PhD): Electrochemical measurement of biological ferrous iron oxidation kinetics on the surface of sulphide minerals

Jean Baptiste Kasongo wa Kasongo(MSc): Investigation of mechanisms and kinetics of ferric leaching in large ore particles

James Mwase (MSc): A preliminary investigation of PGM leaching using organic and inorganic complexing agents

Nomonde Solomon (MSc, co-supervision with Dr Aubrey Mainza): A comparative investigation of the effect of High Pressure Grinding Rollers on mineral liberation

Linus Naik (MSc, co-supervision with Prof. Sue Harrison): Investigation of the mechanisms and kinetics of CO2 uptake during ferrous iron bio-oxidation with Leptospirillum ferriphilum

Jeff Kuhn (MSc, part-time): A comparative study on the kinetics and thermodynamics of Sn chemistry during an acid sulphate leach

Ronnie de Beer (MSc, part-time): Optimisation of a oxidative copper polishing leach

Diane Meintjes (MSc, part-time): Optimisation of Co cementation from a Zn refinery leach liquor

Recently completed theses

Craig Sheridan (PhD, 2007): Constructed Wetlands for the Primary Treatment of Winery Effluent

Thierry Kamunga Kazadi (MSc, 2007): Evaluation of the Redostat™ Device for the Study of Ferrous Iron Biological Oxidation Kinetics

Nneoma Ogbonna (MSc, 2006): Mathematical Modelling of Agglomerate Scale Phenomena in Heap Bioleaching

Recent publications

J. Petersen and D.G.Dixon: 'Modelling Zinc Heap Bioleaching'; Hydrometallurgy Vol. 85 (2-4), 2007, pp 127-143.

J. Petersen and D.G. Dixon: 'Principles, Mechanisms and Dynamics of Chalcocite Heap Bioleaching', in Microbial Processing of Metal Sulfides, E.Donati, W. Sand (eds.), Springer Verlag, Berlin, 2007, ISBN 978-1-4020-5588-1, pp 193-218.

J. Petersen and D.G. Dixon: 'Modeling and Optimisation of Heap Bioleach Processes'; in Biomining, D.E. Rawlings, D.B. Johnson (Eds.), Springer Verlag, Berlin, 2006, ISBN 978-3-540-34909-9, pp 153-176.

T. Ojumu, J. Petersen, G.E. Searby and G.S. Hansford: 'A review of rate equations proposed for microbial ferrous-iron oxidation with a view to application to heap bioleaching', Hydrometallurgy, Vol. 83, No. 1-4, 2006, pp 21-28.

J. Petersen and D.G. Dixon: 'Competitive Bioleaching of Pyrite and Chalcopyrite', Hydrometallurgy, Vol. 83, No. 1-4, 2006, pp 40-49.

N. Ogbonna, J. Petersen and H. Laurie: 'An agglomerate scale model for the heap bioleaching of chaclocite'; Transactions, Journal of the South African Institute of Mining and Metallurgy, Vol. 106, No. 6, June 2006, pp 433-442.

J. Petersen, H. Watling, D. Dixon, P. Franzmann, J. Plumb, J. Johnson, S. Harrison and G. Hansford: 'Progress On The Development Of Comprehensive Understanding And A Model Of Copper Heap Bioleaching Â- The Amira P768 Project'; in Hydrocopper 2005, J.M.Menacho, J.M. Casas de Prada (Eds.), ISBN 956-19-0492-6, Santiago, Chile (2005), pp 333-342.