Abstract

This study investigates the effect of chemical pre-treatment on the electrochemical behaviour and leaching performance of low-grade chalcopyrite ore. Pre-treatment with H?SO?, with or without NaCl, followed by up to 30 days of wetting, promoted copper polysulphide formation and suppressed elemental sulphur, reducing surface passivation. Chloride ions enhanced charge transfer and facilitated the transformation of chalcopyrite into more soluble intermediates. XRD and SEM-EPMA analyses showed structural degradation and rod-like morphologies that improved acid diffusion. Leaching tests at 25 °C demonstrated that NaCl pre-treatment increased copper extraction from 28 % to 51 %, highlighting its potential to improve recovery from refractory ores, while reducing energy consumption and operational costs in heap leaching operations. © 2025 Canadian Institute of Mining, Metallurgy and Petroleum.