Development of silica-modified biochar for sustainable and efficient stabilization of heavy metals in municipal solid...

Municipal solid waste incineration fly ash (MSWI FA) is a hazardous solid waste, and its safe disposal is a global concern. Solidification and stabilization are promising treatment solutions, but there is an urgent need to develop efficient and economical chemical stabilizers to address this major challenge. Herein, we developed a layered silicon-modified biochar (Si-BC) as a chemical stabilizer for immobilizing heavy metals in MSWI FA. Stabilization experiments were conducted by adding 1.0-10.0 wt% Si-BC to evaluate its effect on metal leaching behavior. It was found that adding 2.0 % Si-BC effectively reduced the leaching concentrations of Pb and Cd to meet the GB16889-2008 standard within a wide pH range (7.0-13.0). Species analysis indicated that Si-BC obviously transformed the lead in MSWI FA from a leachable state to a stable state, outperforming commercial stabilizers such as DDTC and Na₂S. BCR analysis revealed that Si-BC exhibits reducing properties, enabling the conversion of metal cations into more stable low-valent states. XPS and FT-IR confirmed that redox reactions and surface complexation contribute to the stabilization of heavy metals. In addition, Si-BC can promote precipitation and physical encapsulation by promoting particle aggregation. This study offers new insights for developing effective MSWI FA stabilizers and highlights the potential of chemical stabilization in solid waste treatment.