The most commonly used collectors for sulfide minerals in the mining industry are the thiol collectors for the recovery of these minerals from their associated gangues by froth flotation. For this reason, a great deal of attention has been paid to understand the attachment mechanism of thiol collectors to metal sulfide surfaces. The density functional theory (DFT) calculations at the B3LYP/3-21G* and B3LYP/6-31++G** levels were employed to propose the flotation responses of these thiol collectors, namely, diethyl dithiocarbamate, ethyl dithiocarbamate, ethyl dithiocarbonate, ethyl trithiocarbonate and ethyl dithiophosphate ions, and to study the interaction energies of these collectors with Ag (+1) ion in connection to acanthite (Ag2S) mineral. The calculated interaction energies, DeltaE, were interpreted in terms of the highest occupied molecular orbital (HOMO) energies of the isolated collector ions. The results show that the HOMOs are strongly localized to the sulfur atoms and the HOMO energies can be used as a reactivity descriptor for the flotation ability of the thiol collectors. Using the HOMO and DeltaE energies, the reactivity order of the collectors is found to be (C2H5)(2)NCS2- > C2H5NHCS2- > C2H5OCS2- > CH5SCS2- > (C2H5O)(OH)PS2-. The theoretically obtained results are in good agreement with the experimental data reported. (C) 2004 Elsevier B.V. All rights reserved.