Facile Synthesis of Fe x O y /C-Based Microwave Absorption Composites under Elevated-Temperature Heat Treatment for the High-Value Utilization of Red Mud

To achieve the high-value utilization of solid waste red mud and the low-cost preparation of efficient microwave absorbers, we recycled red mud (RM) and coal (C) to economically synthesize FexOy/C-based microwave absorbers (named RMCs) via a one-pot method and carbothermal reduction technology. It was found that the magnetic species and carbon crystallinity are sensitive to the carbothermal temperature. Interestingly, the microwave absorption performances of RMC composites display strong inclusiveness to the variable magnetic components with temperature. Benefiting from the suitable magnetic species and graphitization degree of carbon, excellent microwave absorption properties are achieved in the RMC composites. For RMC-700 composites, all of the minimum reflection loss (RLmin) values are less than -30 dB when the coating thickness is above 1.5 mm, and its maximum efficient absorption bandwidth (EAB(max)) covers five-sixths of the Ku band (5 GHz). For RMC-900 samples with a coating thickness of 1.5 mm, the RLmin value could reach -25 dB with a corresponding EAB of 4.16 GHz. An RLmin value of -34.6 dB and an EAB(max) of 4.08 GHz are also obtained in RMC-1000 composites. The above excellent properties are mainly benefited by the strong dielectric loss, which is derived from Fe and its oxide particles as well as graphitized carbon. Moreover, multiple interface polarization and dipole polarization loss provide a guarantee for the powerful attenuation capability of the RMC composite. Impedance matching is also effectively regulated by the changeable magnetic constituents. More importantly, this work provides a direction for the application of recycled red mud, further reducing the environmental pollution caused by its stacking, and is expected to make certain contributions toward protection against electromagnetic radiation.