Formation of Lead Ferrites for Immobilizing Hazardous Lead into Iron-Rich Ceramic Matrix

Abstract

A strategy of immobilizing lead in the framework of ferrite-ceramic matrix, to reduce its environmental hazard was explored in this study. The mechanisms of incorporating lead into lead ferrites (delta-phase (2PbO center dot Fe2O3), gamma-phase (PbO center dot(2-2.5)Fe2O3) and beta-phase (PbO center dot(5-6)Fe2O3)) was revealed by observing the phase transformation in the products. The beta-phase was dominantly formed at low temperature of 700-800 degrees C at Pb/Fe of 1/1 -1/3. The significant growth of gamma-phase was observed at 750-850 degrees C and Pb/Fe of 1/4-1/7. The beta-phase substantially formed at 900-1000 degrees C with Pb/Fe of 1/7-1/12. The transformation of delta-phase to gamma-phase and/or beta-phase indicated the destruction of delta-phase unit and reconstruction of gamma-phase and beta-phase units during sintering process. However, the transformation of gamma-phase into beta-phase suggested a structure conversion process, local structural changes arose as a consequence of the addition of Fe2O3. When comparing the leaching ability of delta-, gamma- and beta-phase, the results showed the superiority of beta-phase for lead immobilization over the longer leaching period. (C) 2018 Elsevier Ltd. All rights reserved.