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Development and testing of a 2D axisymmetric water flow and solute transport model for heap leaching Afewu, Kodjo Isaac

Abstract

Heap leaching is an industrially relevant process for extracting metal values from marginal ores and/or pretreating ores for subsequent extraction of valuable metals. Its advantages include low capital and operating costs, rapid construction times, and relatively low environmental impact. The movement of water and solutes through a heap of ore has serious implications for efficiency of heap leach operations. Solutes (whether introduced into or generated within a heap) move with the water and tend to mix with the bulk solution by the mechanisms of advection and dispersion. Though it is well known that ore-water characteristics influence water flow and solute transport properties during heap leaching, these properties have not been adequately incorporated into the design and operation strategies of heap leaching. In this work, a mathematical model and the results of special laboratory experiments are used to study the reaction and/or transport of solutes during heap leaching. The model is 2D axisymmetric, comprising transport of solutes by advection and dispersion in a bed of broken ore under a point source of solution representing a single drip emitter. The ore hydraulic parameters characterize the water retention and permeability properties, while the transport and chemical parameters affect the distribution of water and solutes, and the rates and extents of reactions of solutes in the heap. The close agreement between the observed data and the predicted results lends credence to the modeling approach and its solution methodology. It was observed that, within the limited water content range relevant to safe and successful operation of a heap leach facility, dispersivity increased with increasing irrigation flux and hence water content. The model captured the trends in water and lixiviant distribution, and solute transport in heaps, clearly demonstrating the importance of incorporating ore hydraulic parameters in modeling heap leaching. It was also found that transport of solutes is slower than leaching and hence the former is the rate limiting step in the process. The model can be used to simulate various process enhancement strategies for efficient operation and optimal design, as well as economic evaluations and potential environmental impact assessment of heap leaching operations.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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