Dithiophosphate-induced hydrophobicity of chalcopyrite and pyrite: coupling adsorption with mineral–specific oxidation

Froth flotation separates chalcopyrite from pyrite based on the difference in surface hydrophobicity, yet chalcopyrite’s intrinsic hydrophobicity is often insufficient for efficient separation without collectors. Dithiophosphate (DTP) collectors are highly selective for chalcopyrite, but microscale comparisons of their effects on chalcopyrite and pyrite remain limited. In this study, chalcopyrite and pyrite were treated with sodium O,O–bis(methylphenyl) dithiophosphate under neutral conditions, and their surface hydrophobicity, topography, and chemistry were characterised using captive–bubble contact angle measurements, Atomic Force Microscopy (AFM), X–ray Photoelectron Spectroscopy (XPS), and Time–of–Flight Secondary Ion Mass Spectrometry (ToF–SIMS). ToF–SIMS detected DTP–derived C 7 H 7 O - fragments on both minerals, and AFM revealed patch–like surface features with heights up to > 100 nm, indicating non–uniform and non–monolayer surface modification by DTP. However, a pronounced increase in hydrophobicity was observed only for chalcopyrite, reaching a maximum at 6 mg/L DTP; higher DTP concentrations produced stronger C 7 H 7 O - signals but lower hydrophobicity, demonstrating that increased collector loading does not necessarily translate into higher hydrophobicity. In contrast, pyrite’s hydrophobicity remained essentially unchanged at all DTP dosages, although ToF–SIMS and AFM confirmed DTP–related species and surface patches. Oxidation analysis showed that DTP treatment induced moderate oxidation on chalcopyrite, accompanied by an increase in metal–deficient polysulphide and elemental sulphur species associated with enhanced hydrophobicity, whereas pyrite experienced more extensive oxidation at both Fe and S sites, forming hydrophilic sulphate/sulphite species. These findings demonstrate that mineral hydrophobicity is not governed by collector adsorption alone; rather, the combined effects of DTP adsorption, mineral specific oxidation pathways, and the structure of the resulting surface layers must be considered.