Comprehensive assessment of thermal characteristics, kinetics and environmental impacts of municipal solid waste incineration fly ash during thermal treatment

Abstract

The volatilization of heavy metals and the release of harmful gases during the thermal treatment of municipal solid waste incineration (MSWI) fly ash (FA) can cause secondary pollution. Understanding the thermal characteristics, heavy metal behaviors and environmental emissions in FA roasting is significant for pollution control and heavy metal elimination. In this work, the thermodynamics, kinetics, environmental impacts, carbon emission, phase transition, leaching toxicity, transition behavior of chlorine and heavy metals in FA thermal treatment were investigated comprehensively for the first time through TG-FTIR, XRD, ICP-OES and IC. The apparent activation energy and thermodynamic parameters were obtained according to the kinetic modeling method. The average apparent activation energy values of the first, second, third, and fourth stages were 60.21, 114.91, 190.23, and 226.67 kJ/mol, respectively, and the reaction control models were chemical reaction model (No.3), assumed random nucleation and subsequent growth model (No.21), assumed random nucleation and subsequent growth model (No.14), and nucleation model (No.10). The environmental impacts illustrate that large amounts of gaseous products, including CO2, H2O, NO and SO2, are released during the thermal treatment of FA, and the emission of CO2 sharply increases as the temperature exceeds 550 °C. When treating 1 kg of FA at 1000 °C, the release of CO2 in stages I, II, III and IV is 0.18, 7.06, 116.34 and 177.21 g, respectively, and the total carbon emission is approximately 300 g. The leaching toxicity of heavy metals in FA is higher below 800 °C, and it is mainly caused by Pb. In addition, the volatilization rate of heavy metals and chlorine increased significantly as the calcination temperature exceeded 800 °C, among which, the volatilization rates of Pb, Cu, and Cl can reach 99.87%, 90.25% and 73.85%, respectively. At high temperatures, heavy metals in FA exist primarily in oxidizable and residual states. The obtained findings can provide theoretical guidance for pollution control and process optimization of FA thermal treatment.