Anodic processes on a galena (PbS) electrode in the presence of n-butyl xanthate studied FTIR-spectroelectrochemically

Anodic reactions on a galena (PbS) electrode in solutions of n-butyl xanthate (X) were studied in situ using attenuated total reflection/FTIR spectroscopy within the -0.5 to +0.7 V potential range in deaerated borate buffer (pH 9.2). It was confirmed that at the first stage X is adsorbed with charge transfer (chemisorbed). It was found that n-butyl dixanthogen, (X)(2), is formed at the reversible potential for the X-/(X)(2) pair, independently of the X concentration. The appearance of dixanthogen makes the surface most hydrophobic, which can be followed from the changes in the water spectrum. Otherwise, the mechanisms of the X adsorption at high and low concentrations have differences. At a concentration of 10(-3) M, oxidative decomposition of galena and adsorbed xanthate is inhibited by the X chemisorption, which is followed by the formation of lead xanthate, Pb(X)(2), and (X)(2). At 8 x 10(-5) M, bulk Pb(X)(2) is formed by the precipitation mechanism. At higher applied potentials first Pb(X)(2) transforms into Pb(OH)(2). Afterward (X)(2) decomposes into a dimer of monothiocarbonate, while galena decomposes into lead sulfite and lead thiosulfate. The possible reactions for these processes were suggested. The results were correlated with the literature data on galena flotation.