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

This investigation was designed to characterize three lead ferrites obtained from the 'ferrite process' for lead removal from wastewater. The three different 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 PbxFe3-xO4. Fe3O4. PbO . nH(2)O as the most probable structure. Electrochemical analysis of the solid lead ferrites was performed using a carbon paste electrode in HClO4 and HCl medium. In each case, the first cyclic-voltammogram showed the participation of solid species in the electrochemical transformation process since the shape of the spectra could be related to the structure and stoichiometry of the ferrites. In second and successive scans, the 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 degrees (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 mechanisms 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.