As near-surface oxide orebodies are depleted, mines are having to process deeper sulfide ores that are lower in metal grade and metallurgically more complex. Modern technologies that are simple, cost effective and environmentally sound are required for their extraction. In many cases, bioleaching is the most suitable process.

Process Design and Costing

Mintek’s Biotechnology Division has developed desk-top flowsheeting, production and costing models for both heap leach and tank bioleach processes, which can be used to provide an initial estimate of project viability. Models have been applied to copper and uranium heap leach projects, as well as bacterial tank leaching of refractory gold and nickel-copper sulfide concentrates. The model uses published information, in-house data and data derived from metallurgical test work. Inputs to the model include parameters such as head grade, leach recovery, leach cycle time or residence time, and the production rate. The model calculates stream flows, equipment or pad/pond sizes, capital cost, operating cost, IRR, NPV and sensitivities. A combination of factored costs and cost indices is used to derive the costs of capital items. Operating costs are calculated from reagent and power consumptions, which are calculated or determined from test work. Reagent, labour and power costs are obtained from published data, vendor quotes, or in-house data.

The Division also provides process design packages for pre-feasibility, feasibility and commercial design of bacterial heap or tank leach operations. Equipment selection, design and costing is performed in conjunction with engineering companies or contractors. Mintek provides process design parameters and operating schedules based on data derived from laboratory and pilot-scale test work. Deliverables include design criteria, capital and operating costs, equipment lists, equipment specifications, piping and instrumentation diagrams, process flow diagrams, and detailed engineering drawings.

Process flow diagram for a nickel-copper bioleach circuit