Mathematical modelling of agglomerate scale phenomena in heap bioleaching
Bioleaching is a naturally occurring process that has been harnessed in metal recovery from low grade ores. The heap bioleaching technique involves complex interactions between chemical reactions, microbial processes and transport processes. The need for efficient heap operations has led to the scientific investigation of heap bioleaching and the development of mathematical models for the process. Over time, the focus of heap leach modelling has moved from models that emphasize particle scale processes to models that emph8size bulk scale processes. In many cases however, the particle scale effects in these bulk scale models are quite simplified. This thesis aims to provide a means for the systematic integration of particle (or micro-) scale processes into bulk (or macro-) scale models for heap bioleaching, by the development of an intermediate (or meso-) scale "agglomerate" model. The agglomerate is defined as a unit volume of a heap that comprises a solid phase (a size distribution of ore particles), a liquid phase (stagnant and flowing leaching solution, which contains dissolved solutes, attached and planktonic microbes) and a gas phase (flowing air and air pockets). The processes incorporated into the proposed model include reagent diffusion and ree1ction in a s.ze distribution of ore particles, microbial attachment, detachment and oxidation processes, and the transport of chemical and microbial species to and from the agglomerate. Isothermal agglomerate conditions, and a uniform distribution of reagents in the stagnant liquid phase, are among the modelling assumptions made. The agglomerate model is applied to investigate the meso-scale bioleaching of a theoretical case study ore that contains mainly chalcocite and pyrite, in the presence of iron oxidizing microbes. The numerical implementation of the model is done in the Python programming language. The integrity of the numerical results is confirmed by performing mass balance checks at the end of each simulation.
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Centre for Bioprocess Engineering Research