Characteristics of the cement-solidified municipal solid waste incineration fly ash

Cement solidification is an important pre-treatment technology for municipal solid waste incineration (MSWI) fly ash into landfill. The physicochemical properties and leaching characteristics are the foundation for assessing the long-term stability of the fly ash solidified with benchmark cement in landfills. The leaching performances of bulk components (Na, K, Ca, Cl, CO₃^2-, and SO₄^2-) and heavy metals (Cu, Zn, Cr, Pb, and Zn) were analyzed based on the percolation column test and pH dependent test respectively. The research showed that in the cement-solidified fly ash, Na and K were mainly in the form of soluble chloride salts and would be washed out severely at the initial leaching stage due to the weak fixation effect of cement. Moreover, a considerable amount of Ca was washed out simultaneously with Na and K, causing a temporary increase in pH value, and then Ca leaching was controlled by the solubility of minerals, mainly calcium carbonate, ettringite formed with CO₃^2- and SO₄^2-. Cement solidification reduced the cumulative release of mobile Cu, Zn, Cr, Pb, and Cd contained in MSWI fly ash. In the cement-solidified fly ash, the leaching of Cu and Zn was controlled by mineral solubility under alkaline conditions, Cr was dependent on the redox conditions, and Pb was related to the complex structures formed with Si-O bonds of silicates. A further research on the long-term stability of the cement-solidified fly ash in landfills was needed.