Ammonia-induced corrosion and modification of chrysocolla surface for enhanced adsorption of sulfide species

The copper content of chrysocolla is an oxidized ore, which has high industrial value in terms of development and utilization. Flotation is generally used to recover such minerals. However, few studies have been conducted on the mechanism of ammonium enhanced flotation in the flotation process of chrysotile asbestos at the atomic level, including the enhanced sulfidation process in solution and mineral surface. This study demonstrated that the presence of NH3 only enhances the reaction between Na2S & sdot;9H2O and Cu ions. The formation of copper-ammonia complexes facilitated the sulfide reaction and led to the generation of more Cu-S species, which can adsorb onto the chrysocolla surface. The NH3 destroys the hydration film of the Cu6[Si6O18]6H2O (1 1 0) surface, creating favorable conditions for sulfidation. The CuS formed in catalytic sulfidation has higher stability compared with CuS formed through direct sulfidation. The NH3 molecule corrosion of the Cu6[Si6O18]6H2O (1 1 0) surface was advantageous in terms of energy, and the formation of Cu(NH3)42+ was -539.32 kJ & sdot;mol-1. After the Cu atom ultimately lost 0.37 e electrons, the Cu-O bond broke, and Cu(NH3)42+ relaxed towards the vacuum layer, which formed a defect at the Cu6[Si6O18]6H2O (1 1 0) surface. The catalytic sulfidation path in the solution was Cu(NH3)4(OH)2 + HS- + 17 H2O + Na+ -> CuS + 4NH3 + OH- + 17 H2O + Na+. The total energy of the reaction was -0.88 kJ center dot mol-1, which indicated that the catalytic sulfidation reaction could spontaneously occur. The CuS generated by catalytic sulfidation was stably adsorbed to the Cu6[Si6O18]6H2O surface of defects through the formation of stable chemical bond between Cu and O. The obtained results revealed the complex interaction between ammonium and minerals, which paves the way for its efficient sulfide flotation.