In Situ Catalytic Pyrolysis of Municipal Sewage Sludge under Calcined Copper Slag: Thermokinetic Analysis and Real-Time Monitoring of Evolved Gases

Copper slag (CS) is a solid waste from the copper pyrometallurgical process. Calcined CS is rich in Fe2O3 and Fe3O4 and has micro amounts of CaO, MgO, Al2O3, ZnO, and CuO, which can be used as catalysts in the thermochemical conversion of municipal sewage sludge (SS). This work aimed to study the in situ catalytic pyrolysis of SS under Calcined CS, including thermal degradation characteristics, pyrolysis kinetics, thermodynamics, and evolution of gaseous products. The results showed that devolatilization of organic substances in SS mainly happened at 150-600 degrees C. The addition of Calcined CS caused the thermal decomposition rate of SS to accelerate and the mass loss to increase. The kinetics of SS pyrolysis with and without Calcined CS were calculated by deconvolution, the Friedman method, and the generalized master plots method, and the results showed that Calcined CS led to a decrease in the apparent activation energy (E alpha) and pre-exponential factor (A), while there was no significant influence on the pyrolysis reaction mechanism (f(alpha)). Online monitoring of SS pyrolysis gases revealed that Calcined CS promoted the formation of CO2, CO, CH4, NH3, C=O, and C=C. However, it had a negative impact on C-O. This study provides insights into coprocessing of the two solid wastes and promotes integrated resource recycling of CS and SS.