A new insight into PCDD/Fs degradation from MSWI fly ash during CaCO₃ oligomer crystallization via low-temperature...

This study investigates the effects of thermal induction on the degradation of PCDD/Fs in municipal solid waste incineration fly ash (MSWI FA) using CaCO₃ oligomer technology, alongside synergistic carbon sequestration. MSWI FA was first treated with CO₂ to prepare CaCO₃ oligomers, achieving a significant carbonation efficiency of 19.1% and stabilizing heavy metals. To promote the orderly crystallization of CaCO₃ and the degradation of PCDD/Fs, CaCO₃ oligomer fly ash (COFA) was thermally treated from 200 to 400 °C under air or nitrogen atmospheres. Thermal induction effectively degraded PCDD/Fs in COFA, with degradation rates positively correlated to temperature based on mass concentration. Under static atmospheric air, degradation rates reached 51.50%, 56.34%, and 92.40% at 200 °C, 300 °C, and 400 °C, respectively. However, elevated temperatures in air might promote the conversion of high-chlorinated PCDD/Fs into more toxic low-chlorinated isomers, increasing the toxicity equivalent concentration. Degradation was more efficient under a nitrogen atmosphere. At 300 °C in nitrogen, over 95% degradation was achieved-approximately three times higher than in air-with minimal gas-phase residues. The solid-phase concentration of PCDD/Fs was reduced to 17.43 ng-TEQ/kg, meeting China's resource utilization standard (HJ 1134-2020), while maintaining a relatively high carbonation rate of 17.2%. This work demonstrates a novel, efficient approach that integrates heavy metal stabilization, PCDD/Fs degradation, and CO₂ sequestration with significantly lower energy consumption compared to conventional high-temperature (>1000 °C) sintering or melting technologies, offering a practical solution for the safe management and resource recovery of MSWI fly ash.