Influence of localized thermal effect of microwave heating on the carbothermic reduction process of ZnFe2O4

As an environmentally efficient method, microwave heating has been proposed to recover Zn from electric arc furnace dust (EAFD) recently. During the process, microwave irradiation has been shown to promote the reaction by lowering the reaction temperature and activation energy, in addition to providing efficient heat. However, the mechanism by which microwave heating promotes the zinc removal reaction of EAFD remains unclear. Thus, this study focused on ZnFe2O4, the primary component of EAFD, and developed an electromagnetic-thermal-chemical reaction coupling model to investigate the factors influencing the carbothermic reduction process of ZnFe2O4 and analyze the promoting mechanism of the microwave on the reaction. The main results indicate that the localized thermal effect, determined by the microwave distribution, exacerbates temperature differences and leads to nonuniform reaction behavior inside the sample. Increasing microwave power and graphite addition enhances the localized thermal effect, worsening field uniformity. In the simulation, the localized thermal effect of microwave heating reduced the activation energy of the zinc removal reaction to 252.97 kJ/mol, with an R2 reaction model. The assistance of the non-thermal effect in enhancing ion diffusion leads to a significant decrease in the activation energy observed in the actual microwave heating experiments.