Abstract
Heap leaching accounts for a fifth of global copper production, sourced primarily from porphyry ores, yet metal recoveries are often not optimal. Gangue, and its interaction with acid, plays an important role in such processes. Thus, a proper understanding of gangue minerals present in the ore, their textural relationships relative to particle size distribution, reactivity with acid under different conditions, and relationship to lithotypes and geological alteration in the orebody, is necessary to predict ore behaviour in the comminution, agglomeration, curing and heap leach unit operations. Mineralogical tools available for characterisation are routine X-ray diffraction, optical microscopy, automated scanning electron microscopy, and electron probe microanalysis, accompanied by more recent advancements in hyperspectral infrared imaging and X-ray computed tomography. Integrated use of these techniques allows mineral abundance, textural relationships and mineral chemistry to be addressed over the range of particle and agglomerate sizes. Additionally, diagnostic leach results can be better interpreted when calibrated against robust mineralogical data. The linkage of ore attributes, metallurgical behaviour and their distribution in the orebody forms an integral part of a geometallurgical approach to predicting, and addressing, changes during the heap leaching process. Further investigation should address the fundamentals of gangue reaction with strong acid, and concomitant structural breakdown during curing and agglomeration processes, and how this differs from gangue-acid reactivity under weaker acid conditions, combined with temperature and fluid flow effects of heap leaching. Pre- and post- characterisation is necessary to understand and quantify the effects of variables for gangue-acid reactivity in these various operations. The characterisation outcomes should lead to a refinement of the hierarchy of gangue mineral reactivity under different conditions of comminution and leaching, and how these in turn relate to identified ore types that are mined.
Highlights
Given the decrease in ore grades with commensurate increase in complexity for processing, heap leaching has, over the last few decades, proven to be an economically viable means to extract such commodities as copper, zinc, nickel uranium and gold [1]
Considering the different unit operations involved in heap leaching, the relative reactivity of these gangue minerals in terms of complete dissolution, the formation of alteration minerals or the precipitation of new minerals from dissolved components needs to be properly understood to enable effective decision-making for optimal copper recovery [6]
This review considers the importance of gangue mineralogy for heap leaching under acid regimes, with a focus on copper porphyry ores
Summary
Given the decrease in ore grades with commensurate increase in complexity for processing, heap leaching has, over the last few decades, proven to be an economically viable means to extract such commodities as copper, zinc, nickel uranium and gold [1]. Considering the different unit operations involved in heap leaching, the relative reactivity of these gangue minerals in terms of complete dissolution, the formation of alteration minerals or the precipitation of new minerals from dissolved components needs to be properly understood to enable effective decision-making for optimal copper recovery [6]. This is especially important given ore variability within and among copper deposits [8,9]. Mineralogical tools are listed and discussed for pre-and-post reaction characterisation that could be conducted as part of an integrated or geometallurgical approach, which is considered essential for predicting ore behaviour during the heap leaching operations
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