Preparation of ceramicby sintering MSWI fly ash synergistically with silica-aluminum solid waste and heavy metalsolidification mechanism

The high leaching toxicity of heavy metals in MSWI fly ash poses a serious threat to human health and ecological environment. In order to solve the technical bottleneck faced by the traditional fly ash sintering technologies, which is caused by chlorine-promoted reaction leading to the volatilization of heavy metals and the difficulty of ceramics in high-calcium and low-silica-aluminum systems, the synergistic disposal process of ‘membrane concentrate leaching-ceramic formation of multi-source solid wastes’wasdesigned, and the heavy metal solidification system of CaO-SiO₂-Al₂O₃-NaF was constructed. This study showed that: membrane concentrate leaching removed 98.46% of soluble chlorine salts in fly ash; leaching residue (50%), overhaul slag (15%) and waste glass (35%) were sintered at 1050℃ for 20 min to prepare 900-grade high-strength ceramic. The solidification rates of heavy metals Pb, Cd, Cr, Cu and Zn were 40.52%, 70.22%, 88.45%, 76.12% and 90.19% respectively, and the mechanisms were as follows: Pb, Cu and Zn were cured mainly by chemical bonding to form crystals such as (PbF₂)_12.7(PbO)_58.2(SiO₂)_28.4, CuO, Ca₂Zn₂SiO₇, etc., respectively. Cr and Cd were solidified mainly through ion substitution to form crystals such as Na₆Ca₂Cr₆Si₆O₂₄(SO₄)₂, CdMgSi₂O₇, etc. A few of CdS, PbCl₂ and PbS were physically sequestered via ceramic pores and CaF₂-based solid matrix. In summary, the synergistic preparation of ceramic from multi-source wastes expands the new path of ‘waste for waste, synergistic use’, and provides theoretical support and engineering solutions for the safe disposal of hazardous wastes containing heavy metals.