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

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.