Chemical and electrochemical characterization of lead ferrites produced inthe purification of lead-bearing wastewater

This investigation was designed to characterize three lead ferrites obtaine d from the 'ferrite process' for lead removal from wastewater. The three di fferent compounds, obtained according to the starting Fe2+/Pb2+ molar ratio ((Pb0.04Fe0.96Fe2O4)-Fe-II-O-III. nH(2)O; (Pb0.07Fe0.93Fe2O4)-Fe-II-O-III. nH(2)O and (Pb0.17Fe0.83Fe2O4)-Fe-II-O-III. nH(2)O for ratios of 15/1, 7/1 or 3/1, respectively) were subjected to XRF and chemical analysis (ICP-AES and potentiometric titrations), and to XRD, DSC and FTIR which indicated P bxFe3-xO4. Fe3O4. PbO . nH(2)O as the most probable structure. Electrochemi cal analysis of the solid lead ferrites was performed using a carbon paste electrode in HClO4 and HCl medium. In each case, the first cyclic-voltammog ram showed the participation of solid species in the electrochemical transf ormation process since the shape of the spectra could be related to the str ucture and stoichiometry of the ferrites. In second and successive scans, t he voltammograms indicated the redox couples Fe-ads(3+) + le(-) double left right arrow Fe-ads(2+) and Pb-ads(2+) + 2e(-) double left right arrow Pb d egrees (s) in HClO4 and FeCl2 (+)(ads) double left right arrow FeClads+ and PbCl2 (s) + 2e(-) double left right arrow Pb (s) + 2Cl(-) in HCl. These me chanisms were confirmed by the half-peak potentials and the displacement of the peaks associated with HCl activity. (C) 1999 Elsevier Science Ltd. All rights reserved.