A density functional based tight binding (DFTB+) study on the sulfidization-xanthate flotation mechanism of cerussite

Abstract

Cerussite (PbCO3) has now attracted increasing attention due to the increasing demand of Pb metal and rapid depletion of Pb−S minerals. Sulfidization-xanthate method is effective to recover PbCO3. In this paper, density functional based tight binding (DFTB+) method was employed to discuss microscopic mechanism of cerussite sulfidization. Sulfidization model of a PbS film forming on PbCO3 surface was established based on coordination chemistry of mineral flotation, changing ligand type of Pb from O ligand to S ligand. The results showed that after sulfidization surface Pb exhibited significant surface relaxation, leading to enhanced activity of Pb4f and Pb5f 6p orbitals. Density of state (DOS) analysis indicated that S ligand strengths nephelauxetic effect of Pb atoms, resulting in stronger covalent effect of Pb−S bonding compared with Pb−O bonding. Sulfidization turned Pb2+ from hard acid in PbCO3 to soft acid in PbS, making it easier to interact with butyl xanthate (soft base) but harder to interact with water (hard base). Calculation results showed that adsorption energy of water becomes less negative after sulfidization, whereas formation energy of water and xanthate co-adsorbed on sulfidized surface becomes more negative, suggesting calculation results agree with the prediction of hard and soft acids and bases (HSAB) theory.