Voltammetric investigations show that chemisorption is the thermodynamically favoured process in the interaction of thiol collectors with sulphide minerals, The potential dependence of chemisorption coverage is in accordance with the Frumkin adsorption isotherm, Chemisorbed thiols render sulphide mineral surfaces hydrophobic and induce efficient flotation of mineral particles. W-Visible, Fourier transform infrared, surface-enhanced Raman scattering, and electron spectroscopic studies provide complementary information on the nature of the adsorbed species, X-ray photoelectron spectroscopic (XPS) studies of xanthate on galena reveal sulphur environments associated with chemisorbed xanthate and lead xanthate but no oxidised sulphur derived from the galena substrate, This finding is explained by electrochemical studies that have shown the surface composition of oxidized galena to relax, Discrepancies between the results of conventional and synchrotron radiation excited XPS studies of the oxidation of galena are discussed.