Conversion of waste incineration fly ash into Al-substituted tobermorite by hydrothermal treatment

Al-substituted tobermorite has been successfully synthesized by hydrothermal treatment at 180°C in the presence of NaOH solution, using waste incineration fly ash as a starting material, pretreated with repeatedly washing and heating at 800°C. The relation between Al-substituted tobermorite yield and synthetic conditions has been also examined. The pretreatment was essential to convert fly ash into Al-substituted tobermorite with reproducibility, and the Al-substituted tobermorite yield was found to reach a maximum in the fly ash treated with 2 M (mol·dm^-3) NaOH for 20-30 h. The order of Al-substituted tobermorite yield was 2 M≫3.5 M≅1 M>0.5 M≫6 M, with respect to NaOH concentration. With increasing the NaOH concentration and extending the reaction time, sodalite and cancrinite generated as minor phases. The fly ash treated with 2 M NaOH for 30 h showed the best removal characteristics and took up about 0.5 mmol·g^-1 for both Cs⁺ and NH₄⁺ ions. The uptake amounts of resulting products were found to depend on the Al-substituted tobermorite yield.