Coal fly ash (CFA)

bentonite

kaolin and diatomite were selected as silicon-aluminium additives and tobermorite crystal were synthesized as seed added. Synergistic effect of silicon-aluminium addition and seed-induced on stabilization of heavy metals including Pb

Zn

Cu

Cd

and Cr in municipal solid waste (MSW) incineration fly ash (FA) during hydrothermal process under 150℃ was studied. Zeolites could not be formed by hydrothermal treatment (HT) mainly due to the high content of Ca but low content of Si

Al in FA

which led to the leaching toxicity of Pb (5.45 mg·L-1) beyond the limited value of non-hazardous waste. Hibschite or katoite were found in HT products with 10% mass of additives solely or combined added. Tobermorite could be successfully synthesized with higher 30% mass of additives solely or combined added

which was attributed to the proper element of Ca/(Al+Si) adjusted near 0.67-1.20. Leaching toxicity of Pb in HT products decreased to 0.30 mg·L-1 with 30% mass of combined additives including CFA and diatomite(1:1)

and it decreased to lowest level (0.28 mg·L-1) with more 3% mass of seed added which owing to the effective synthesis of tobermorite from first 6 h. Furthermore

seed-induced hydrothermal treatment of FA with combined silicon-aluminium additives could cause the inhibition of heavy metals migration into liquid during hydrothermal process. The decrease of heavy metals in liquid phase

and the decrease of leaching toxicity of heavy metals in solid phase (HT products) were observed

which indicated that heavy metals were really stabled in solid phase.