Mechanism of di-isobutyl dithiophosphinate adsorption onto galena and pyrite E.T. Pecina a, * , A. Uribe b , J.A. Finch c , F. Nava b a CIMAV, SC (Centro de Investigacion en Materiales), Quimica de Materiales, Miguel de Cervantes 120, Compl. Ind. Chihuahua, C.P. 31109, Chihuahua, Chih., Mexico b CINVESTAV-IPN, Unidad Saltillo, A.P. 663, C.P. 25900, Ramos Arizpe, Coah., Mexico c McGill University, Montreal, Canada H3A2B2 Received 13 May 2005; accepted 7 October 2005 Available online 21 November 2005 Abstract 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. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Mineral Processing; Flotation collectors; Sulphide ores; Redox reactions 1. Introduction Non-conventional collectors (i.e., collectors different to xanthates) are more frequently used in the Mexican sul- phide flotation practice (Uribe-Salas et al., 2000), mainly due to both the presence of silver values and pyrite or pyrrhotite as sulfide gangue minerals. An example of non-conventional collectors is sodium-di-isobutyl dith- iophosphinate (DTPINa), known under the trademark of Aerophine 3418A of Cytec Industries (Fig. 1). DTPINa is mainly recommended to float lead, copper and precious metals from minerals containing high levels of pyrite, as is the case of polymetallic ores. Research works on froth flotation of sulfides in the pres- ence of non-conventional collectors (e.g., dithiophosphi- nates, thionocarbamates, etc.) have demonstrated that the selective activation of the mineral species, is substantially affected by the electrochemical conditions (pulp potential) of the flotation slurry (Gorken et al., 1992; Uribe-Salas et al., 2000). In spite of this, very little fundamental data are available on the electrochemical response of sulfides in presence of DTPINa. It is known that the interaction mechanism of thiol col- lectors and sulfides is essentially the same. Nevertheless, examinations of non-conventional collectors such as thio- nocarbamates (Basilio and Yoon, 1992), MBT (Maier and Dobia ´s, 1997), etc., have revealed some differences with regard to the xanthates. For example, a chemisorption process (with no electron transfer) that proceeds at lower potentials compared with the potentials at which the elec- trochemical adsorption of xanthates occurs. According to Basilio and Yoon (1992), this behavior is due to the small pK of the corresponding metal–collector compound. Although it is believed that DTPI  interacts with sulfides through mechanisms analogous to those accepted for 0892-6875/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2005.10.004 * Corresponding author. Tel.: +52 614 4394845; fax: +52 614 4391112. E-mail address: teresa.pecina@cimav.edu.mx (E.T. Pecina). This article is also available online at: www.elsevier.com/locate/mineng Minerals Engineering 19 (2006) 904–911