Enhanced flotation recovery of malachite via mechanical intensification in a high-Mg2+ system: Microstructural evolution and interfacial electrochemical behavior

In high-Mg 2+ wastewater systems, the sulfidization flotation of malachite is severely inhibited. This study systematically investigated the effect of mechanical sulfidization on the flotation behavior of malachite in comparison with conventional stirring sulfidization. Pure mineral flotation tests showed that in a 100 mmol/L Mg 2+ solution, mechanical sulfidization achieved a maximum malachite recovery of 83.77%, significantly superior to stirring sulfidization. Actual ore flotation further confirmed that the copper recovery increased from 74.16% to 84.33% using mechanical sulfidization. Characterization results indicated that mechanical sulfidization effectively reduced magnesium ion adsorption on the malachite surface, promoted the rapid formation of Cu S hydrophobic species with a higher Cu(I) proportion, suppressed hydrophilic Cu–SO species, and generated a denser sulfidization layer. Electrochemical measurements revealed that mechanical sulfidization facilitated xanthate oxidation and constructed a stable hydrophobic barrier. DFT calculations further demonstrated that the mechanically sulfidized surface exhibited a higher Cu S bond population and a significantly lower activation energy barrier for xanthate oxidation than stirring sulfidization. In summary, mechanical sulfidization constructs a highly covalent Cu S network enriched with Cu(I) that lowers the kinetic barrier for xanthate oxidation, effectively alleviating the interference of high Mg 2+ ions. This study fills the gap in understanding the surface chemical states and electronic structure mechanisms underlying mechanical activation in malachite sulfidization flotation, providing a theoretical basis for high-Mg 2+ wastewater recycling in copper oxide ore flotation.