Transformation of hazardous lead into lead ferrite ceramics: Crystal structures and their role in lead leaching.

This study quantitatively determined the transformation of lead into lead ferrite ceramics and examined the influence of structural defects in lead ferrites (i.e. Pb2Fe2O5, PbFe4O7 and PbFe12O19) on lead leaching. Mechanisms of metal incorporation were examined from quantifying the phase compositions of lead ferrites in the products of sintering lead oxide with hematite. At low-temperature of 700°C, Pb was preferentially incorporated into the Pb2Fe2O5 crystals, and the incorporation efficiency ranged from 25.7 to 97.5% depending on different Pb/Fe molar ratios. By increasing temperatures to 750-850°C, Pb2Fe2O5 was subsequently reacted with hematite for the formation of PbFe4O7 and PbFe12O19 in Pb/Fe of 1/4 and 1/12 systems. PbFe12O19 was found to be the high-temperature (1000°C) stable phase for incorporating lead, and the incorporation efficiency ranged from 28.6 to 92.1% by different Pb/Fe molar ratios. Leaching tests demonstrated that PbFe12O19 was more resistant to acid attack than Pb2Fe2O5 and PbFe4O7. The crystal structural defects in Pb2Fe2O5 and PbFe4O7 were determined to be the factors influencing their intrinsic phase durability. On the other hand, PbFe12O19 was relatively free of structural defects and was found to be the preferred stabilization product to reduce the environmental hazard posed by lead.