The Optimal Design of Bioleaching Processes

Abstract

The development of bioleaching processes has reached the point where the relevant question is not “Do they work?”, but “How can they be made to work at the lowest possible total cost?”. Designers of the next generation of processes must consider not only conventional heap leach and slurry-tank systems, which were developed from non-biological extraction techniques, but also designs that follow logically from the unique, autocatalytic, autotrophic and product inhibited nature of bioleaching kinetics. Such processes are conceptualized here in terms of the residence times distributions of the four phases they contain, water, solids, biomass and air. How should they differ from each other, and how might the optimum configuration be approximated in practice? The economic viability of most large-scale bioprocesses depends on achieving a high mean cell residence time either by cell recycle or immobilization, and this insight must be transferred to bioleaching. Since it takes longer to process a large mineral particle than a small one, the optimum solids RTD is one in which the residence time increases with particle size. The standard bioprocess engineering result that a continuous bioprocess should consist of a completely-mixed section, followed by a plug-flow section, must be modified for the solid nature of the substrate and for cell recycle.

Keywords:

• Bioleaching
• process design
• residence times
• scale up