Effects of curing pathways and thermal-treatment temperatures on the solidification of heavy metal in fly ash by CaCO3 oligomers polymerization

Abstract

The solidification of the heavy metals (HMs) of municipal solid waste incineration fly ash (MSWI FA) by a calcium carbonate polymer is a novel approach. The effects of different curing pathways and thermal-treatment temperatures on the leaching concentrations of the HMs were investigated by conducting different leaching tests and performing an overall pollution toxicity indices (OPTI) analysis of the leaching data, respectively. The results showed that the solidification efficiencies of the Pb and Zn of FA samples, which could form carbonate-bound states, from the fly ash-CaCl 2 ▪2H 2 O wet carbonation pathway were above 99.5%. The samples from the pathway that involved mixing FA with calcium carbonate oligomers (CCOs) had lower leaching concentrations of Cd and Cr (0 and 0.1112 mg▪L −1 ). With the thermal treatment temperature increasing from 105 °C to 500 °C, the treated FA samples had larger particle sizes, fewer pores, and more compact surface structures covering much more calcite , and the solidification efficiencies of Pb and Zn increased from 64.3% to 98.8% and from 60.2% to 98.9%, respectively. The calcium carbonate structure was decomposed in an acidic leaching agent, so the solidification effects were weakened and even negative. In contrast, the treated FA samples achieved effective solidification of HMs by physical packaging and chemical precipitation in the HT/J 557–2010 standard and the OPTI decreased from 8126.39 to 44.88. Therefore, a nonacidic environment is suitable for the storage or resource utilization of FA samples prepared by this method. • Two different curing methods of MSWI fly ash using CaCO 3 polymer were studied. • Inhibition on heavy metals leaching of 500 °C heat treatment was better than 105 °C. • The leaching characteristics of the samples were evaluated by different standards. • Fly ash samples were subjected to comprehensive heavy metal toxicity assessments.