Formation of lead ferrites for immobilizing hazardous lead into iron-rich ceramic matrix

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 (δ-phase (2PbO·Fe2O3), γ-phase (PbO·(2-2.5)Fe2O3) and β-phase (PbO·(5-6)Fe2O3)) was revealed by observing the phase transformation in the products. The δ-phase was dominantly formed at low temperature of 700-800 °C at Pb/Fe of 1/1-1/3. The significant growth of γ-phase was observed at 750-850 °C and Pb/Fe of 1/4-1/7. The β-phase substantially formed at 900-1000 °C with Pb/Fe of 1/7-1/12. The transformation of δ-phase to γ-phase and/or β-phase indicated the destruction of δ-phase unit and reconstruction of γ-phase and β-phase units during sintering process. However, the transformation of γ-phase into β-phase suggested a structure conversion process, local structural changes arose as a consequence of the addition of Fe2O3. When comparing the leaching ability of δ-, γ- and β-phase, the results showed the superiority of β-phase for lead immobilization over the longer leaching period.