Surface modification of hemimorphite via ammonium chloride and its response to flotation

[Display omitted] This paper focused on the catalytic sulfidation of hemimorphite to examine the promotional effect of NH4Cl on surface sulfidation and its impact on the flotation performance. The interaction mechanism between NH4Cl and the hemimorphite surface in the sulfidation flotation system was clarified. Micro-flotation tests were conducted using the sulfidation-xanthate flotation method. Compared with direct sulfidation, adding 2.5 × 10−4 M ammonium chloride to the flotation system increased the maximum flotation recovery of hemimorphite by about 18 %. AFM and SEM-EDS analysis revealed that NH4Cl dissolved the hemimorphite surface and destroyed its structure. This exposed more Zn sites and enhanced the sulfidation of the hemimorphite surface. FTIR spectroscopy indicated that adding NH4Cl promoted the adsorption of xanthate components on the hemimorphite surface, which formed more hydrophobic substances. XPS analysis of the hemimorphite surface suggested that NH4Cl complexed with Zn species on the hemimorphite surface, which enhanced the reactivity of HS− and S2−, thus improving the floatability. Further ToF-SIMS analysis confirmed that catalytic sulfidation produced a thicker and denser ZnS layer on the hemimorphite surface. Its surface activity was superior to that obtained by direct sulfidation, showing that NH4Cl improved sulfidation flotation performance of hemimorphite. DFT results confirmed that catalytic sulfidation can occur spontaneously·NH3 species separated from the hemimorphite surface and returned to the solution, and stable Zn-S covalent bonds were formed on the hemimorphite surface. These results provide a potential method for promoting the recovery of zinc oxide minerals.