A DFT study on the structure-reactivity relationship of thiophosphorus acids as flotation collectors with sulfide minerals: Implication of surface adsorption

Abstract

Thiophosphorous compounds: diisobutyl dithiophosphate (DIBDTPA), diisobutyl dithiophosphinate (DIBDTPI), diisobutyl monothiophosphate (DIBMTPA) and diisobutyl monothiophosphinate (DIBMTPI) are widely used as flotation collectors and corrosion inhibitors, though the true nature of their bonding mechanisms to solid surfaces is still unclear. Using density functional theory (DFT) calculations, this study investigates the structure-reactivity relationship of these thiophosphorus molecules as flotation collectors with sulfide minerals. The results indicate that the O atom(s) bonded to the P atom in thiophosphorus molecules can significantly impact the chemical reactivity of the S atom(s) in the four reagents, and for DIBMTPA and DIBMTPI, they could even attend the chemical bond formation with metal atoms. The reactive power of the four compounds to mineral surfaces of Cu, Au, Ag and Pb sulfides is predicted to be DIBDTPI≫DIBMTPI≥DIBDTPA>DIBMTPA, and their flotation selectivity against pyrite and sphalerite is suggested as DIBDTPA<DIBDTPI<DIBMTPI<DIBMTPA. Moreover, the thione form of acid or ion species of DIBMTPA or DIBMTPI is more stable than its thiol form, and in aqueous phases, the ionized thione of the four thiophosphorus collectors exhibits the strongest affinity to mineral surfaces. The theoretical results provide an atomic level understanding of the adsorption activity and selectivity of the four thiophosphorus molecules to metal sulfide minerals and a potential approach to molecular design of new thiophosphorous compounds for improving the flotation recovery of them.