Investigating variables affecting heap (bio)leaching through determining access to sub-surface mineral grains by micro-scale X-ray tomography

Heap bioleaching is a hydrometallurgical technology used to facilitate the extraction of valuable metals such as copper, gold, nickel, and uranium from low-grade, typically sulphidic, ores. This process is highly complex due to the interactions of various sub-processes, including the flow of leaching solution around ore particles, mass and heat transfer, chemical reactions, and microbially-mediated reactions. Critical to the efficiency of the bioleaching process is the contact between the leaching solution and mineral grains, which is necessary for the oxidation of sulphide minerals. Nevertheless, many mineral grains are located beneath the surfaces of ore particles, and interaction with the leaching solution occurs primarily through micro-scale cracks and pores. This study aims to investigate the factors that affect access to these sub-surface mineral grains, utilizing micro-scale X-ray tomography to analyze the exposed surface area of these grains. Initial findings indicate that the slow leaching rates and constrained recovery of metals in heap systems can largely be attributed to the challenges presented by these non-surface mineral grains, highlighting the need for improved strategies in heap bioleaching to enhance metal recovery rates.