Direct flotation recovery of malachite using a novel N-substituted hydroxamic acid: Adsorption mechanism and DFT calculation

The weak collection ability of conventional benzohydroxamic acid (BHA) impedes its widespread application in the direct flotation of copper oxide minerals. Conversely, octyl hydroxamic acid (OHA) with enhanced hydrophobicity demonstrated superior collecting ability while exhibiting weak selectivity in malachite flotation. In order to achieve a balance between collecting ability and selectivity, we synthesized a novel N-cyclohexyl-N-hydroxyacetamide collector (ECHA) that featured similar structure of hydroxamate compounds and improved selectivity for the direct flotation of malachite. The bench-scale flotation results demonstrated that ECHA exhibited stronger collecting ability and excellent selectivity, 14.66% and 15.17% of copper recoveries increased than sodium butyl xanthate (SBX) and BHA, respectively. Contact angle tests, Zeta potential tests and solution chemistry analysis revealed that the interaction intensity of ECHA with malachite was significantly stronger than that of calcite and quartz. FTIR and XPS analysis showed that the reaction sites of ECHA were primarily located on the [–N(OH)CO–] group, suggesting possible chemisorption on the malachite surface. Additionally, DFT calculations indicated that the ECHA anion could potentially form a five-membered structure chelate complex with a Cu atom on the malachite surface through its [–N(OH)CO–] functional group. ECHA proved to be promising as an attractive collector in the direct flotation of malachite.