Flotation of a Copper Oxide–Sulfide Ore Using NaHS-Assisted Sulfidization and 2,5-Dimercapto-1,3,4-Thiadiazole (DMTD) as a Collector: Experimental and DFT Insights

Flotation of mixed copper oxide–sulfide ores remains challenging due to low natural floatability of oxide minerals and complex interplay between sulfidization and collector adsorption. This study investigated the combined effect of NaHS-assisted sulfidization and 2,5-dimercapto-1,3,4-thiadiazole (DMTD), an azole-based collector, in terms of enhancing copper recovery from a mixed oxide–sulfide ore. The effects of pulp pH, DMTD, NaHS, and sodium metasilicate dosages, together with pulp solid concentration, were evaluated using response surface methodology. The quadratic model showed high predictive capability (R2 = 0.9361), identifying NaHS dosage as the most influential factor. Optimum operating conditions (pH 9.50, DMTD 200 g/t, NaHS 750 g/t, sodium metasilicate 500 g/t, and 25% solids) yielded 64.03% copper recovery. Compared with the plant collector (PAX, Potassium Amyl Xanthate), DMTD increased recovery by 12.6% for highly oxidized ore while producing a higher concentrate grade. Density Functional Theory (DFT) calculations provided molecular insights into the experimental observations, confirming DMTD’s high affinity for sulfidized surfaces. Hybrid solvation models revealed greater thermodynamic stability (ΔEads = −6.74 eV) than PAX due to hydrogen bonding with explicit water molecules, while the smaller HOMO–LUMO gap (ΔEgap = 0.86 eV) supported its superior electron transfer capability and reactivity. These findings demonstrate that NaHS-assisted sulfidization with DMTD is an effective strategy for improving flotation of copper oxide–sulfide ores.