Effects on high content of MSWI fly ash for the deterioration and immobilization performance of blast furnace slag-desulfurization gypsum-based binder

The high concentrations of heavy metals, dioxins, and soluble salts in municipal solid waste incineration fly ash (MSWI FA) posed significant environmental challenges. This study introduced a novel MSWI FA-blast furnace slag-desulfurization gypsum-based binder (FBCM) as an innovative solution for hazardous waste immobilization and sustainable waste management. The results revealed that a high MSWI FA content (40 similar to 60 %) reduced the compressive strength of FBCM, while still effectively immobilizing heavy metals and toxic dioxins, with no leaching risk. Microscopic analyses revealed that increasing the MSWI FA content raised the Ca/Si ratio and reduced the crystallinity of C-(A)-S-H gels. After 360 days of hydration, at 60 % MSWI FA content (pH = 9.90), hexa-coordinated Al preferentially reacted with SO42- to form ettringite, with the highest content of ettringite (56 %). Strip-shaped ettringite occupied the main microscopic voids, leading to a loss of strength in the FBCM due to the absence of C-(A)-S-H gel cementation. In contrast, at 40 % MSWI FA content (pH = 11.01), the presence of various heavy metals and anions caused the cracking of ettringite, with a length of 6 similar to 8 mu m and a width of 3 similar to 5 mu m. X-ray absorption fine structure (XAFS) analyses indicated that increasing MSWI FA content increased the structural disorder (sigma(2)) and the Zn-O coordination bond length of Zn2SiO4 in FBCM. This study presented a sustainable approach for the harmless disposal of MSWI FA and offered theoretical support for its application in waste management and resource recovery.