Effectively immobilizing lead through a melanotekite structure using low-temperature glass-ceramic sintering.

This work evaluated the feasibility of using low-temperature thermal immobilization based on the reaction mechanism forming the melanotekite (Pb2Fe2Si2O9) crystal phase to stabilize lead (Pb) containing waste. X-ray diffraction demonstrated that Pb could be incorporated into the melanotekite structure at easily attainable treatment temperatures (less than 500 °C) by magnetite and SiO2 precursors. The γ-Fe2O3 intermediate was found to play a key role in initializing melanotekite crystallization at a much lower temperature than that in traditional thermal immobilization techniques. Although a higher sintering temperature may increase Pb incorporation efficiency, amorphization occurred at temperatures higher than 950 °C. In addition, Pb was found to partition more in the amorphous phase of the SiO2-rich matrix. The results of the prolonged toxicity characteristic leaching procedure revealed a substantial improvement in the acid resistance of the targeted crystallized product sintered at 850 °C compared with the amorphous product and the other oxide products. The results of batch adsorption and subsequent thermal treatment verified the possibility of using the melanotekite structure to stabilize aqueous Pb with the Fe3O4@SiO2 residue. The study demonstrated that the melanotekite structure can be used to immobilize both solid and aqueous Pb through low-temperature thermal stabilization.