Transformation of hazardous lead into aluminosilicate ceramics: structure evolution and lead leaching

This study investigated crystallization mechanisms for the formation of lead aluminosilicate by sintering lead stabilization with kaolin-based precursors. PbAl₂Si₂O₈ was found to be the only stable lead aluminosilicate in low-PbO system and demonstrates its highly intrinsic resistance to acid attack in leaching test. A three-stage PbAl₂Si₂O₈ formation mechanism was supported by the results of the changing temperature in the system. Amorphization of sintered products was observed in both PbO/kaolinite and PbO/mullite systems at 600-700°C. When the temperature was increased to 750-900°C, the crystallochemical formation of lead aluminosilicates (i.e., Pb₄Al₄Si₃O₁₆, Pb₆Al₆Si₂O₂₁, and PbAl₂Si₂O₈) was observed. Pb₄Al₄Si₃O₁₆ and Pb₆Al₆Si₂O₂₁ were found to be the intermediate phases at 700-900°C. Finally, PbAl₂Si₂O₈ was found to be the only crystallite phase to host Pb at above 950°C. A maximum of 80% and 96.7% Pb can be incorporated into PbAl₂Si₂O₈ in PbO/kaolinite and PbO/mullite systems, respectively, but the final products exhibited different microstructures. To reduce environmental hazard of lead, this strategy demonstrated a preferred mechanism of immobilizing lead into PbAl₂Si₂O₈ structure via kaolin-based precursors.