In this work, both the density functional theory (DFT) calculation and X-ray photoelectron spectroscopy (XPS) were conducted to investigate the depression mechanisms of cyanide on the flotation performance of chalcopyrite. The density functional theory calculation results showed that cyanide could be adsorbed on a chalcopyrite (112) surface spontaneously, which preferably occurred on the surface Fe–Fe hollow site. Both C and N atoms of cyanide could bond with Fe atoms of the chalcopyrite (112) surface, while the interaction of Fe–C bond was more intense, where the Fe 3d orbital donated electrons to the hybrid sp orbital of a C atom forming a back-donating bond. XPS analysis indicated that the chemical interaction between cyanide and surface Fe atoms occurred, resulting in the generation of a hydrophilic iron–cyanide complex on the chalcopyrite surface, which deteriorated the flotation performance of chalcopyrite.

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Ammonium salt is a common collector in coal reverse flotation. This study compared the difference of adsorption behavior on ammonium salt Lilaflot D817M between sub-bituminous coal and silica as well as the surface characteristic change after being processed by ammonium salt. The results indicate that the adsorption capacity of sub-bituminous coal is always higher than that of silica under different experimental conditions, such as different initial concentrations of ammonium salt, different adsorption times, different concentrations of the depressant dextrin, and different pH values. Ammonium salt could increase the isoelectric point of both silica and sub-bituminous coal greatly. However, the hydrophobicity of silica enhances much more significantly than that of sub-bituminous coal after being treated by Lilaflot D817M. This indicates that the surface wettability change degrees of sub-bituminous coal and silica after being treated by ammonium salt are not proportional to the adsorption capacity because of their different surface structures. The reverse flotation test result shows that 2 kg/t Lilaflot D817M dosage could help obtain relatively good flotation indexes.