Novel insight of the thermal degradation kinetics, environmental impact and transformation behavior of heavy metals and chlorine of municipal solid waste incineration fly ash in nitrogen

Abstract

Thermal treatment is an effective method to dispose of municipal solid waste incineration (MSWI) fly ash (FA), however, present research mainly focuses on the thermal behavior of FA in air, neglecting the investigation of FA pyrolysis characteristic in inert gases. The weight loss, phase transition, environmental impact, and conversion behavior of heavy metals and chlorine during the FA pyrolysis in N2 were measured using TG-FTIR-XRD-ICP-IC to increase understanding of the transformation process and decomposition features of FA in inert gas. The results demonstrated that CO2, NO, C-O(H), HCl, SO2, and H2O are emitted during FA pyrolysis due to the decomposition of inorganic salts and organic compounds. After being roasted at 1200 °C, the volatilization rates of As, Cr, Cd, Cu, Pb, and Zn were 56.71%, 34.75%, 99.56%, 83.41%, 96.22%, and 97.19%, respectively. However, the removal rate of Cl was only 51.43%, owing mostly to the formation of Ca2SiO4CaCl2 at high temperatures, which hampered chlorine volatilization. The kinetic of FA pyrolysis was investigated using FWO, KAS, and CR methods at heating rates of 10, 20, 30, and 40 °C/min, which suited the experimental data of each stage well. Chemical reaction (No. 2), assumed random nucleation and its subsequent growth (No. 11), and three-dimensional diffusion and spherical symmetry (No. 21) were the reaction control procedures of stages I, III and IV, with activation energies of 54.04, 213.03 and 280.85 kJ/mol, respectively. The degradation kinetics, environmental emissions, and reaction mechanisms of FA pyrolysis in the N2 atmosphere can provide a novel insight for pollution reduction and process optimization.