XPS and FTIR study of the influence of electrode potential on activation of pyrite by copper or lead

Abstract

Activation of pyrite by either copper or lead ions and subsequent xanthate adsorption on activated surfaces were studied in aqueous solutions of pH 5, 6.5 and 9 under different electrochemical conditions using X-ray Photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). At pH 5, the copper concentration on the surface of pyrite increased strongly when the electrode potential was changed towards cathodic direction. At low activation potentials ( E h≤+100 mV), a change in the chemical state of sulfur on the surface was observed by XPS proposing formation of a copper-containing surface sulfide phase. In electrochemically-controlled xanthate adsorption, the behavior of copper-activated pyrite resembled that of chalcopyrite (CuFeS 2). The results indicate that activation of pyrite by copper at pH 5 can be controlled by the potential of the mineral. At pH 9, the copper content on the surface was independent of the potential of pyrite and no changes were observed in chemical state of sulfur if compared to unactivated pyrite in the potential region −100 to +400 mV (SHE). In the case of pyrite activation by lead, no changes were observed in sulfur spectra at either pH 5 or 9 at different electrode potentials. The concentration of lead on the surface increased at pH 5 when potential was changed towards cathodic direction. All lead present at the surface of pyrite was concluded to be in the form of lead(II)-oxygen species and no evidence of exchange between lead and iron was found. Both adsorbed xanthate and dixanthogen were observed on the surface of Cu-activated pyrite after activation at cathodic potentials (−100 to +50 mV) and subsequent treatment in either ethyl or amyl xanthate solution of pH 5 or 6.5 at potential region +350 to 550 mV (standard hydrogen electrode, SHE). In a similar experiments with Pb-activated pyrite, only a faint indication of the adsorbed collector species was found proposing that lead rather depresses than activates pyrite.