Utilisation of municipal solid waste incinerator (MSWI) fl y ash with metakaolin for preparation of alkali-activated cementitious material

The proper treatment on hazardous municipal solid waste incineration fly ash (MSWIFA) is important. The application of alkali-activation technology to prepare alkali-activated MSWIFA (AAFA) material provides a potential not only to immobilise the heavy metals, but also to trigger its pozzolanic property in manufacturing building material. In this study, in addition to investigate the feasibility of alkaline activation technology in preparing AAFA with sodium silicate activator, the effect of metakaolin in AAFA (AAFM) was also explored to enhance its performance. The results showed that, compared to the AAFA, blending 10 % metakaolin in AAFA significantly improved both 28-day and 90-days compressive strengths, which was almost 200 % higher than that of AAFA. The compressive strength was increased with increasing the dosage of sodium silicate. The C-S-H gel was observed as the main hydration product of AAFA and AAFM. Moreover, the ettringite was observed in AAFM due to the reaction between the CaSO4 in MSWIFA and aluminate phase from metakaolin. Finally, the 28 and 210-day leaching behaviours of AAFM on Zn, Cu, Pb, Cd, Cr and Ni were successfully suppressed to less than 1 % of that originally from MSWIFA, which can meet the requirement from Chinese standards.

Automated summary

The application of alkali-activation technology to prepare alkali-activated MSWIFA material holds potential to immobilize heavy metals and enhance its pozzolanic property for manufacturing building material. Adding metakaolin in AAFA significantly improves compressive strength, with the addition of sodium silicate increasing strength further. AAFA and AAFM successfully suppress leaching behaviors of certain metals to meet Chinese standards.