Double roles of sodium hexametaphosphate in the flotation of dolomite from apatite

Abstract

Sodium hexametaphosphate (SHMP), as a common flotation agent, is widely used in various mineral processing. In this study, effects of SHMP on the flotation of fine apatite and dolomite were investigated. It was proved to play a role as depressant for both of the minerals by single and artificially mixed minerals flotation, while the effective improvement of apatite concentrates under low amount SHMP addition demonstrated that it worked as another unknown role. Solution chemistry analyses, zeta potential measurements, X-ray photoelectron spectroscopy (XPS) and DLVO calculation were carried out to systematically investigate the corresponding mechanism of SHMP effect in the flotation process. DLVO theory calculation verified the dispersion function of SHMP for mineral particles. Hence, SHMP played double roles in the flotation process. On the one hand, it worked as a depressant by increasing the hydrophilicity of apatite, through promoting the formation of CaHPO4 and Ca(H2PO4)2 on the apatite surface. On the other hand, it acted as a dispersant by increasing the total interaction energy between apatite and dolomite mineral particles, enhancing the dispersion of dolomite and adhesion of agents and bubbles to the minerals. Both roles were favorable for the separation of mixed minerals in flotation.