Abstract
Heap leach operations typically employ some form of modelling and forecasting tools to predict cash flow margins and project viability. However, these vary from simple spreadsheets to phenomenological models, with more complex models not commonly employed as they require the greatest amount of time and effort. Yet, accurate production modelling and forecasting are essential for managing production and potentially critical for successful operation of a complex heap, time and effort spent in setting up modelling tools initially may increase profitability in the long term. A brief overview of various modelling approaches is presented, but this paper focuses on the capabilities of a computational fluid dynamics (CFD) model. Advances in computational capability allow for complex CFD models, coupled with leach kinetic models, to be applied to complex ore bodies. In this paper a comprehensive hydrodynamic CFD model is described and applied to chalcopyrite dissolution under heap operating conditions. The model is parameterized against experimental data and validated against a range of experimental leach tests under different thermal conditions. A three-dimensional ‘virtual’ heap, under fluctuating meteorological conditions, is simulated. Continuous and intermittent irrigation is investigated, showing copper recovery per unit volume of applied leach solution to be slightly increased for pulse irrigation.
Highlights
World ore deposits of copper are becoming lower in head grade with copper sulphides, chalcopyrite being the predominant mineralogy [1]
The method of heap leaching is a low-cost technique that can often achieve high recoveries from oxide ores, typically greater than 70% depending upon the kinetics of reaction
Heap leaching requires balancing operational parameters to optimise a complex suite of interacting gas- solid-liquid-thermal physics that cannot be captured with simplistic models
Summary
World ore deposits of copper are becoming lower in head grade with copper sulphides, chalcopyrite being the predominant mineralogy [1]. Capturing the dynamics of a large heap leach operation, with width and depth of hundreds of meters and time scales of months and years is very challenging due to the complex interactions between the ore particles, fluid, thermal, bacterial and oxygen activity. There are considerable differences in the various heap leach models, and the modelling method employed to predict the heap leach operation very much depends on functionality requirements, together with cost, accuracy and time constraints. Providing a true representative ‘virtual heap’ which dynamically responds to operational and environmental changes requires all the complex interacting physics of the gas-solid-liquid-thermal heap matrix to be accounted for, arguably making the additional time and cost of a phenomenological model, setup and calibration, profitable for any long-term heap operation. In the micro-scale model, the mineral dissolution rate is dependent upon the current concentrations in the local fluid, where the macro models (fluid matrix, air matrix and thermal conditions) provide the inputs to the particle dissolution models
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