The effect of the alkyl chain length and ligand type of thiol collectors on the heat of adsorption and floatability of sulphide minerals

Collector performance in the base metal sulphide (BMS) and platinum group mineral (PGM) flotation industry depends on both the polar head group and the non-polar hydrocarbon chain length of the collector. These affect the strength of the collector-mineral bond, as well as the extent of hydrophobicity imparted. This study investigated the effect of alkyl chain length and ligand type on both the heat of adsorption of thiol collectors onto sulphide minerals and the hydrophobicity which these imparted. Isothermal titration calorimetry (ITC) and microflotation techniques were employed to measure the heat of adsorption and recoveries, respectively. Sulphide minerals investigated were chalcopyrite, pyrite and pyrrhotite. Thiol collectors investigated were xanthates of varying chain length (ethyl, isobutyl, n-butyl and amyl xanthate); dithiocarbamates (diethyl DTC and n-butyl DTC) as well as diethyl dithiophosphate. Both the heat of adsorption and microflotation recoveries increased with increasing collector chain length for xanthate homologues on all mineral types. There was a positive linear correlation between the heats of adsorption and microflotation recoveries. However, this relationship was not sustained for collectors with different ligand types. The heat of adsorption of diethyl-DTC was always higher than that of diethyl-DTP for all the minerals. In fact, diethyl-DTP barely interacted with any of the sulphide minerals although it produced unexpectedly high chalcopyrite recoveries. It was found that the heat of adsorption is not a robust indicator of hydrophobicity for collectors of different ligand types. However, for collectors of the same ligand type, but differing alkyl chain lengths, it is a strong predictor of hydrophobicity.