Impact of mineral dissolution-precipitation on pore geometry during copper sulphide heap leaching

Heap leaching of copper sulphide ores involves complex dissolution and secondary precipitation reactions that alter pore geometry and influence extraction efficiency. This study employed micro-CT (5.5 mu m resolution) and pore network modelling to rigorously quantify these changes, examining the effects of flow rate, lixiviant composition (acid-only, NaCl, AlCl3), and particle size. Proton-promoted dissolution in acid-only media at low flow rates significantly increased macroporosity by dissolving siliclastic gangue yet yielded only similar to 10 % copper extraction due to proton depletion and limited sulphide dissolution. In contrast, combined ferric-iron and proton-promoted dissolution in NaCl and AlCl3 media enhanced chalcopyrite dissolution within gangue fissures, achieving 25-95 % copper recovery, with AlCl3 leaching of coarse particles at high flow rates proving most effective. However, high ferric iron concentrations triggered jarosite precipitation via hydrolysis, reducing pore connectivity. Homogeneous precipitation gradually decreased permeability across the heap, while heterogeneous precipitation on mineral surfaces created preferential flow paths or short-circuits, complicating lixiviant distribution. Particle size further modulated these dynamics such that fine particles reduced tortuosity, prolonging lixiviant-ore contact and enhanced recovery, whereas coarse particles increased tortuosity and channelling, limiting effective leaching area. Though the micro-CT resolution constrained detection of thin passivation layers, these findings elucidate pore structure evolution and its impact on leaching efficiency. Overall, the study offers strategies to optimize copper yields by tailoring lixiviant and flow rate to mitigate hydrological inefficiencies and precipitation-induced changes through staged irrigation and ore blending, offering a framework for efficient, ore-specific heap leaching operations.