The interaction of sodium-di-isobutyl dithiophosphinate (DTPINa) with galena and pyrite in alkaline media (pH 9) was examined using cyclic voltammetry, open circuit potential and contact angle techniques. Analysis of results suggests that the collector interacts with the minerals by chemical and electrochemical mechanisms according to the following steps: a chemisorption process (without electron transfer) that takes place when the collector interacts with metal species (e.g., of lead) that shows chemical affinity towards the collector; an electrochemical-chemical process developed by the galena that involves two steps: the oxidation of the mineral (electrochemical step) and the formation of a metal-collector precipitate (chemical step); and an electrochemical process (adsorption of collector and dimer formation) that occurs when pyrite is held at a redox potential sufficiently anodic to produce oxidation of the collector. (C) 2005 Elsevier Ltd. All rights reserved.