The ability of static secondary ion mass spectrometry to discriminate submonolayer from multilayer adsorption of thiol collectors

Abstract

Experiments have been carried out to establish whether static time-of-flight secondary ion mass spectrometry (ToF-SIMS) alone is able to differentiate monolayer and multilayer coverage of thiol collectors on sulfide minerals. The systems investigated were those for which X-ray photoelectron spectroscopy is able to provide an independent determination of the extent of coverage, and included diethyldithiophosphate (DTP) and 2-mercaptobenzothiazole (MBT) on chalcocite, DTP on Ag 2+ ∂ S, and iso-butyl xanthate (BX) and MBT on galena. For adsorption of a thiol collector (TC) on copper and silver sulfides, TC and metal(TC)H ions were detected for both monolayer and multilayer coverage. For multilayer coverage only, metal(TC) 2 ions were evident, notwithstanding the fact that other spectroscopic measurements had revealed the stoichiometry of the principal multilayer species to be metal(TC). For adsorption on galena, TC and metal(TC) ions were observed for both monolayer and multilayer coverage, whereas for multilayer coverage only, fragment ions from Pb(TC) 2 and (TC) 2 species were evident. Indeed, for all the systems studied, static ToF-SIMS was able to distinguish monolayer from multilayer coverage. However, differentiation was reliable only when both positive and negative secondary ion spectra were determined, and possible only because the multilayer species on copper and silver sulfides included a low concentration of metal dithiolate. In light of those findings, unequivocal differentiation by means of static SIMS is expected to be possible for all thiol collector/sulfide systems.