Mechanism of mixed dithiophosphate and mercaptobenzothiazole collectors for Cu sulfide ore minerals

Abstract

The species adsorbed on Cu sulfide ore minerals from alkaline or near neutral solutions of blends of the flotation collectors dibutyl dithiophosphate (BDTP) and 2-mercaptobenzothiazole (MBT) have been established by X-ray photoelectron spectroscopy. Adsorption on air-exposed Cu metal, cuprite, chalcocite, covellite, chalcopyrite and pyrite was investigated from relatively high concentration solutions to simulate processing of variably oxidised ores or slug addition of collector under plant conditions, as well as from solutions of lower concentration. For air-exposed Cu metal, it was found that for a typical BDTP-MBT blend in which di-n-butyl DTP predominated, negligible BDTP was adsorbed at high concentration unless the pH was below 7. By contrast, at low concentrations but under non-starvation conditions, BDTP adsorption predominated even in the alkaline pH range. Both BDTP and MBT species were adsorbed following sequential conditioning in the two collectors. The dithiolate (MBT)2 was not adsorbed from high concentrations of the blend, whereas it was adsorbed from similar concentrations of MBT collector alone. Most of the observed behaviour can be explained by collector solution species reactivity with Cu decreasing in the order MBT− > BDTP− > HMBT. There was no evidence to suggest any surface chemical synergism between the two collectors. For the minerals, competitive chemisorption broadly similar to that for Cu metal was observed, but the formation and adsorption of multilayer molecular CuBDTP or CuMBT was lower, and that of (MBT)2 and HMBT was higher, when the surface availability of Cu was lower than at a native oxide layer. Open circuit potentials for Cu metal, chalcocite and covellite electrodes in 10−3 M solution of the collector blend were lower than for the corresponding values in MBT collector alone. For all concentrations in the alkaline pH range, surfaces conditioned in either BDTP alone or the blend were obviously hydrophobic, whereas surfaces conditioned in high concentrations of MBT were not obviously hydrophobic. Some surfaces conditioned sequentially in the two collectors, or in high concentrations of the blend at a pH below 7, were only moderately hydrophobic. Thus, depending on the collector concentration and pH, direct (albeit ex-situ) surface chemical characterisation established the adsorption of different species from a BDTP-MBT blend compared with sequential conditioning in the individual collectors, and hence potentially different hydrophobicities.