Variation of PCDD/Fs and Their Monomer Components During Low-Temperature Thermal Decomposition (250–500 °C) of Municipal Solid Waste Incineration Fly Ash
This study investigates the variation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and their monomer components during low-temperature thermal decomposition (250–500 °C) of municipal solid waste incineration fly ash from a typical mechanical grate furnace. Results demonstrate that pyrolysis temperature and time significantly affect the solid-phase removal rates of PCDD/F mass concentration and toxic equivalent (TEQ) concentration. The influence weights of temperature on mass and TEQ removal rates are 20.86 and 21.41, respectively, while those of time are 4.27 and 3.36. Response surface analysis identifies optimal conditions at 380 °C for 1.0 h. At 250–300 °C, both PCDFs and PCDDs concentrations increase synchronously, indicating enhanced formation. At 300 °C for 2.0 h, high-chlorinated congeners undergo dechlorination to low-chlorinated ones, notably increasing 2,3,7,8-T4CDD (I-TEF=1.0) and 1,2,3,7,8-P5CDD (I-TEF=0.5). From 350 °C upward, significant degradation occurs; at 380 °C (1.0 h), degradation rates for PCDDs and PCDFs reach 97.8% and 97.6%, respectively, effectively reducing TEQ-contributing congeners. The process proceeds in two stages: initial dechlorination, followed by destruction of dioxin-like compounds at higher temperatures. 2,3,7,8-T4CDD emerges as a critical component for detoxification. These findings provide a scientific basis for optimizing thermal treatment of fly ash to minimize environmental and health risks.