Microwave-Assisted Reduction of Electric Arc Furnace Dust with Biochar: An Examination of Transition of Heating Mechanism

This present study aimed to investigate the reduction behavior of hazardous electric arc furnace (EAF) dust in the presence of biochar (reducing agent) based on self-reduction of their composites under microwave irradiation with an emphasis on the microwave heating mechanism. The experimental results showed that after microwave-assisted reduction the iron metallization degree of the product reached 94.7%, much higher than that (67.6%) by conventional heating. It was revealed that the "lens effect" promoted the directional migration of the gangue elements and the newly generated metallic iron component in the microwave field. Further analysis of electromagnetic characteristics of the composite system demonstrated that its self-reduction relied heavily on the microwave heating mechanism, which underwent multiple transitions during the reduction process. The dielectric polarization and magnetic loss dominated the initial stage of microwave heating (stage I, <873 K), promoting volumetric heating. In the following stage (stage II, 873-1073 K), the dielectric polarization intensified as the dielectric parameters kept increasing due to the strong reduction reactions of Fe3O4 and ZnFe2O4. In stage III (>1073 K), the conductive loss became more apparent because of the release of volatiles and increase of the newly generated metallic iron phase, producing enhanced electronic conduction that was expected to speed up the reduction process.