Selective Passivation Mechanisms of Chalcocite during Cu–Mo Flotation Separation: Experimental Analysis and Interfacial Reaction

The effect of the Fenton reagent, an environmentally compatible oxidant, on the separation of chalcocite and molybdenite was systematically investigated in this study. Microflotation tests revealed that the Fenton reagent exerts a significantly stronger depressive effect on chalcocite than on molybdenite, enabling efficient separation of the two minerals. At fixed sodium butyl xanthate (SBX) concentration and kerosene concentration of 5 × 10^-5 mol/L and Fenton reagent concentration ([FeSO₄]/[H₂O₂] = 1:1) of 1 × 10^-4 mol/L, under pH = 6, the separation was further enhanced, with chalcocite recovery dropping to 0.05% and molybdenite recovery reaching 95.03%. In the artificial mixed mineral system, both SBX concentration and kerosene concentration of ([SBX]/[kerosene] = 1:1) 5 × 10^-5 mol/L and Fenton reagent concentration ([FeSO₄]/[H₂O₂] = 1:1) of 1 × 10^-4 mol/L, under pH = 6, Cu recovery declined substantially from 89.42 to 12.76%, while Mo recovery remained at 87.24%, yielding a recovery differential of 74.48%. Surface characterization through LEIS, AFM, SEM-EDS, and contact angle measurements revealed that Fenton reagent treatment selectively increased the hydrophilicity of chalcocite. Chalcocite exhibited significantly higher increases in impedance, roughness, and surface oxygen content compared to molybdenite, indicating more extensive surface oxidation. ToF-SIMS analyses and XPS further confirmed strong oxidation on chalcocite surfaces, in contrast with only mild oxidation on molybdenite. This differential oxidation facilitated the formation of Cu(OH)₂, which acts as the primary depressant on chalcocite, thereby effectively depressing its floatability. The DFT results indicate that the adsorption energy of ^•OH molecules on the Cu sites on the surface of chalcocite is -144.79 kJ/mol and the bond length of Cu-O is 2.187 Å, with a population of 0.28. The adsorption energy of ^•OH molecules on the S sites on the surface of molybdenite is -7.85 kJ/mol, the bond length of S-O is 3.541 Å, and the population is close to zero. This suggests that ^•OH molecules are more likely to interact with the copper sites on the surface of chalcocite (001). Overall, as a stable, effective, and environmentally compatible oxidant, the Fenton reagent demonstrated strong potential for the industrial separation of copper-molybdenum sulfides.