Effect of curing temperatures on geopolymerization and heavy metal solidification in alkali-activated zeolite/MSWI fly ash specimens

Admixtures of pozzolanic materials or solid wastes with municipal solid waste incineration fly ash (MSWIFA) can improve heavy metal stabilization/solidification (S/S) properties in alkali-activated MSWIFA specimens. In this work, the compressive strength of MSWIFA admixes with zeolite activated by Na2O center dot 1.7SiO(2)center dot nH(2)O (FZNS) specimens with different curing times (3, 7, 14, and 28 d) and temperatures (20, 50, and 80 degrees C) is investigated. The results reveal that a 40 wt% zeolite replacement of MSWIFA in FZNS specimens (FZNS40) not only increases the early compressive strength by 129% but also reduces strength loss during continuous high-temperature (50 or 80 degrees C) curing. Moreover, zeolite addition promotes the creation of geopolymers at 28.5 degrees C-30.5 degrees C in X-ray diffraction (XRD) curves. During 50 or 80 degrees C curing, the NaCl peak disappears and a marginal Friedel's salt peak can be detected at 11.4 degrees C. The gel contents are more concentrated on C-S-H in FZNS0 and C-(A)-S-H/N-A-S-H in FZNS40, as demonstrated by differential thermogravimetry (DTG) and magic angle spinning nuclear magnetic resonance (MAS NMR) analysis. With zeolite addition, long-time and high-temperature curing can improve the heavy metal solidification ratio in FZNS specimens. After high-temperature curing, the honeycomb or cluster morphologies of the gel products, visible by scanning electron microscopy (SEM) in the FZNS specimens, reveal high heavy metal stabilization properties. It is easier to form the fibrous C-(A)-S-H/N-A-S-H gel near zeolite owing to the high content of SiO2 and Al2O3. Zeolite modifies the compressive strength, high-temperature stability, and heavy-metal S/S efficiency in FZNS specimens, which promotes the utilization of MSWIFA as an ecological resource in the future.

Automated summary

The addition of admixtures of pozzolanic materials or solid wastes with municipal solid waste incineration fly ash (MSWIFA) can enhance the stability and solidification properties of alkali-activated MSWIFA specimens. By replacing 40% of MSWIFA with zeolite activated by Na2O center dot 1.7SiO(2)center dot nH(2)O (FZNS), the compressive strength of FZNS specimens can be increased by 129% and strength loss during high-temperature curing can be reduced. Zeolite addition also facilitates the formation of geopolymers and improves heavy metal solidification in FZNS specimens. The modification of compressive strength, high-temperature stability, and heavy-metal stabilization efficiency by zeolite promotes the future utilization of MSWIFA as an ecological resource.