Anodic oxidation of galena (PbS) studied FTIR-spectroelectrochemically

The attenuated total reflection/FTIR spectra of the (100) galena/electrolyt e interface were measured in situ for the first time in nitrogen-saturated borate buffers (PH 9.2) of two concentrations in the potential region of -0 .5 to +0.7 V (SHE), simultaneously with the voltammograms. The experiments were conducted on the electrode previously reduced at -0.5 V and the nonred uced electrode as well. Not only vibrational bands but also monotonic absor ption of free carriers was analyzed. It was concluded that at the first ste p galena is oxidized by the reaction PbS + 2xh(+) --> Pb1-xS + xPb(2+), whi ch is followed by the reaction PbS + 2h(+) double right arrow Pb2+ + S degr ees . Pb(OH)(2) is formed by the precipitation mechanism. The Pb(OH)(2) yie ld of galena oxidation increases as either the buffer concentration or the time of the galena reduction is increased, which was explained by an increa se in the potential drop in the Helmholtz layer. When a more positive bias potential is applied, lead sulfite and thiosulfate are formed by the reacti ons PbS + 3H(2)O double right arrow PbSO3 + 6H(+) + 6e and PbS + S degrees + 3H(2)O --> PbS2O3 + 6H(+) + 8e, respectively. These processes were correl ated with the galena floatability.