DFT study of sulfidization mechanism of cerussite (PbCO3) and smithsonite (ZnCO3)

The differences in the sulfidization mechanism of cerussite (PbCO₃) and smithsonite (ZnCO₃) were comparatively studied by the density functional theory (DFT) method. Pb−S/Zn−S layers over PbCO₃/ZnCO₃ surfaces are constructed to simulate the sulfidization structure. The results of layer distance and Mulliken charge suggest that Pb−S layer formed over PbCO₃ is stable but Zn−S layer formed over ZnCO₃ is unstable. Because of the high covalency of Pb−S layer and the high ionicity of Zn−S layer, the sulfidization−xanthate method is effective for cerussite but ineffective for smithsonite flotation. To recover smithsonite, strong ionicity collectors are required, and hence the sulfidization−amine method is applied more to smithsonite flotation. These differences in the sulfide layer structure and flotation behavior of PbCO₃ and ZnCO₃ surfaces are mainly attributed to the different polarizabilities of the metal ions (Pb²⁺ and Zn²⁺) and the ligands (O ligand and S ligand) and the inertness of Zn²⁺ 3d¹⁰ orbital.