Acid-Gangue Interactions in Heap Leach Operations: A Review of the Role of Mineralogy for Predicting Ore Behaviour

Abstract

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.

Pretreatment to Leaching for a Primary Copper Sulphide Ore in Chloride Media

“…It can be concluded that there was low acid consumption to dissolve the gangue phases in the sample. These results are in accordance with those obtained by Chetty [28], in which species such as quartz and muscovite were considered of low solubility in an acid media. For the tests at 25 • C, the presence of unreacted chalcopyrite was determined.…”

“…According to By et al [27], species such as quartz and biotite are not reactive against the presence of sulphuric acid. Muscovite was also declared to be of low reactivity in acid media [28]. Furthermore, pyrite is an inert sulphide, strong oxidants have to be employed for its efficient dissolution, and no such conditions exist in the proposed treatment [29].…”

Leaching of Copper Concentrate with Iodized Salts in a Saline Acid Medium: Part 1—Effect of Concentrations

“…The slight increase in pH during leaching is due to the dolomite present as well as biotite, which, according to studies, is one of the most acid-reactive silicates [ 67 , 68 ], while to a lesser extent muscovite and albite [ 69 ]. Although the latter is less soluble in acid, grain size plays an important role in reactivity.…”

Gangues and Clays Minerals as Rate-Limiting Factors in Copper Heap Leaching: A Review

“…Silicates are the most common minerals in Earth's crust and mantle, making up 95% of the crust and 97% of the mantle by most estimates. Thus, it is necessary to understand their reactivity under the sulfuric acid regimes used in heap leaching to predict the behavior of the mineral and its impact on operations [60].…”