A thermochemical study of thiol collector surface reactions on galena

Abstract

The mechanism whereby thiol collectors adsorb onto a mineral surface has been widely studied. Most of these studies examine the mineral surface at equilibrium state and, often, well above monolayer coverage. However, the formation of species at the mineral surface is a complex process that is both kinetically and thermodynamically controlled. This study uses isothermal titration microcalorimetry to measure the heat evolved during the reaction of a variety of different thiol collectors and collector mixtures with a galena mineral surface.It was observed that, for ethyl xanthate (SEX) and isobutyl xanthate (SIBX), there are sequential reactions occurring at the mineral surface at sub-monolayer coverages. A proposal is put forward for the reactions based on literature and the microcalorimetric, dissolution and pH data from this investigation. DTC (isobutyl dithiocarbamate) had very similar heats of reaction to the xanthates. The major difference was that there was no secondary reaction noticed in the case of DTC. This led to the postulation that the reaction mechanism was different in the case of DTC, with DTC reacting directly with the galena surface. DTP (diethyl dithiophosphate) showed no reaction with the galena surface at all and this was confirmed with adsorption isotherm studies. Enthalpies of reaction of mixtures of SEX with DTP were an additive effect of the enthalpies of each of the pure collectors, meaning that addition of DTP lowered the enthalpy of the SEX reaction proportionally to the amount of DTP added. There was no evidence of a synergistic reaction occurring between the xanthate and the DTP as suggested by previous flotation experiments. This suggests that there is an alternative reaction mechanism occurring to explain improved flotation performance when using SEX-DTP mixtures with galena.