P-31 CP/MAS NIVIR spectroscopy was used to study the adsorption of six different O,O '-dialkyldithiophosphate ions on the surface of synthetic galena (PbS). The P-31 CP/MAS NIVIR spectra of the surface lead(II) dithiophosphates were compared with the P-31 CP/MAS NIVIR spectra of polycrystalline lead(II) dithiophosphate complexes of the same ligands. Surface complexation of the dialkyldithiophosphate ions was established on the surface of PbS. A terminal S,S '-chelating coordination is suggested for the surface complexes. The bulkier alkyl groups lead to surface precipitation in addition to the surface adsorption. Derivatives of monothiophosphoric and phosphoric acids were displayed as hydrolysis products of dialkyldithiophosphates on the synthetic PbS, the amount of which depends on the type of alkyl group. (C) 2008 Elsevier Inc. All rights reserved.