Selective Kinetic Separation of Chalcopyrite from Complex Iron Sulfide Gangue: Synergistic Impacts of Pulp pH, Green Depressants, and Sulfhydryl Collectors

The selective separation of chalcopyrite from pyritic ores represents a major industrial challenge due to inadvertent copper activation. This study systematically investigates the batch flotation kinetics of a complex sulfide ore (Draa Sfar North, Morocco) using a first-order kinetic model (R2>0.916). The impacts of pulp pH, chemical depressants, and specialized collectors were evaluated to optimize the copper/iron selectivity index (SICu/Fe). The results reveal a high-alkalinity paradox: At pH 11.0, chalcopyrite kinetics experience a severe passivation bottleneck (Ki,Cu=0.1330 min−1). At pH 11.5, selectivity collapses (SI=2.64) due to persistent iron sulfide floatability (Ki,Fe=0.2066 min−1). Conversely, natural pH (≈6.0) provides a superior baseline (SI=3.32), where 40 g/t sodium cyanide (NaCN) yielded a peak index of SICu/Fe=10.25. As an eco-friendly substitute, sodium lignosulfonate (LSNa) achieved outstanding performance (SICu/Fe=5.30), reducing iron kinetics to their lowest level (Ki,Fe=0.0356 min−1) via ferric–anionic complexation. Furthermore, Danafloat 271 secured the highest collector-driven selectivity (SICu/Fe=5.03) by suppressing the iron matrix (Ki,Fe=0.0306 min−1) following Hard–Soft Acid–Base principles. This study clarifies specific aspects of selective copper–iron flotation, demonstrating that natural pH circuits with green depressants or selective collectors offer a sustainable alternative.