In Situ FTIR−Spectroelectrochemical Study of the Anodic Processes on a Galena (PbS) Electrode under Open-Air Conditions in the Absence and Presence of n-Butyl Xanthate

Abstract

Anodic reactions on a galena (PbS) electrode were studied in situ using attenuated total reflection/Fourier transform infrared spectroscopy within the −0.5 to +0.7 V (standard hydrogen electrode) potential range in air-saturated borate buffer (pH 9.2) in the absence and presence of n-butyl xanthate. Compared to the deaerated conditions, the anodic decomposition of galena is increased by 2−3 times, being accompanied by the enhanced precipitation of Pb(OH)2 both in the absence and presence of xanthate at low concentrations. The increased precipitation rate of Pb(OH)2 is explained by acceleration of the incongruent dissolution of galena (PbS + H2O + 2h+ ⇒ S° + H+ + Pb(OH)+ ) which is caused by an increase in the potential drop in the Helmholtz layer due to the oxygen adsorption. As in the case of the deaerated xanthate solutions, the formation of bulk lead xanthate is preceded by chemisorption of xanthate, and dixanthogen is formed with no overpotential. However, at low concentrations of the reagent, lead xanthate is formed by the precipitation mechanism against the anodic decomposition of galena. At more anodic potentials, this species is substituted by lead hydroxide. At high concentrations of xanthate, xanthate chemisorption inhibits the electrochemical dissolution of galena and the decomposition of adsorbed lead xanthate mediating the formation of lead xanthate and, at higher potentials, that of both lead xanthate and dixanthogen.