Improving the performance of incineration fly ash as cement admixture by high-temperature sintering and its toxic leaching characteristics

During the incineration disposal of municipal solid waste, a large quantity of incineration fly ash (IFA) will be produced. IFA contains many heavy metals and dioxins; It is a hazardous solid waste. High-temperature disposal plays a vital role in harmless and resource recovery. In this paper, the direct sintering IFA (D-IFA) is prepared without adding any other substance, the composite sintering IFA (C-IFA) is prepared with adding a certain quantity of fly ash (FA) from coal-fired power plants, while un-sintering IFA is called U-IFA. The effects of direct and composite sintering on the physicochemical properties of incineration fly ash, and the properties of cement prepared with C-IFA, D-IFA and U-IFA, are comparatively investigated. The results show that after composite sintering (IFA: FA = 9:1), the pozzolanic activity of C-IFA increased from 67.95% of U-IFA to 80.57%, forming two new minerals - Larnite and Ye'elimite; The decomposition rate of chloride and dioxin is 88.06% and 99.94%. However, after direct sintering, the pozzolanic activity of D-IFA is only 58.74%, lower than that of U-IFA, only forming one new mineral – Larnite; The decomposition rate of chloride and dioxin is 22.39% and 99.56%. The cement with C-IFA at 20% dosage, has water requirement of 26.61%, the 3 d and 28 d compressive strength cement of 33.3 MPa and 46.7 MPa. The cement with D-IFA at 20% dosage, has water requirement of 27.83%, the 3 d and 28 d compressive strength cement of 30.5 MPa and 38.2 MPa. There are not much differences among the water requirements of cements prepared with C-IFA, D-IFA and U-IFA. Compared with 3 d and 28 d compressive strength of cement prepared with U-IFA of 32.8 MPa and 43.2 MPa, the 3 d compressive strength of cement with C-IFA little changes, the 28 d the compressive strength significantly increases, but both 3 d and 28 d compressive strengths of cement prepared with D-IFA decrease. However, according to the limits of Cl− and dioxins in cement of Chinese national standards, the allowed dosages of C-IFA and D-IFA in cement can reach up to 12.50% and 1.92%, while U-IFA is not allowed as admixture to add in cement. Composite sintering consumes excessive CaO, improves pozzolanic activity, significantly reduces chlorine and dioxin content, increases the dosage of IFA in cement, and contributes to the harmless and resource utilization of IFA.