Understanding gangue acid consumption in copper sulfide heap leaching: Predicting the impact of carbonates, silicates and secondary precipitates

Abstract

A geometallurgical model, linked to simple ore body characteristics, was established to understand short- and long-term gangue acid consumption (GAC) variability for a new copper sulfide chemical heap leaching process under standard metallurgical conditions, including an acid dose of 12 kg/t sulfuric acid during agglomeration at a particle size of 80% passing ¾”. Carbonate availability, or liberation, defined as a function of feed grade and alteration type, enabled the calculation of short-term GAC when combined with mineral abundance, assuming stoichiometric behavior. An adjustment to the acid balance needed to be applied for jarosite formation, which was made possible via a linear correlation, again related to carbonate feed content. The long-term GAC component of the ore could then be determined by difference, comparing data from the column program to the estimation of the two previous variables, resulting in the identification of biotite and chlorite as key drivers of long-term acid consumption during leaching. Final inputs for the three-stage approach to predict overall GAC were simplified to carbonate (CO3), magnesium (Mg), and iron (Fe), facilitating implementation in the 3D resource block model. Application of this methodology indicated that the magnitude of long-term GAC is reduced when higher levels of acid are consumed during the initial phases of processing. The study clearly shows how a holistic knowledge of the ore body can provide an in-depth understanding of future processing response, enabling key investment decisions to be made appropriately, prior to mine construction.