Recycling of red mud to Fe/C-based composite microwave absorbents by coal gasification semi-coke

Fe/C-based composite microwave absorption (MA) materials were prepared by high temperature solid phase reaction between coal hydrogasification semi-coke (SC for short) and solid waste red mud (RM). In order to optimize MA performance, initial system composition was changed. It was found that, under an argon atmosphere and reaction temperature of 900 ℃, the composites obtained from systems with mass ratio of SC to RM (MR_SR) at 0.4∶1−0.7∶1 all showed excellent performance, and that corresponding to MR_SR of 0.6∶1 was the best. At a coating thickness of 1.5 mm, the simulated minimum reflection loss and effective absorption bandwidth could reach −48.3 dB and 4.6 GHz, respectively. The strong intrinsic attenuation ability mainly resulted from the dielectric loss due to the presence of graphite carbon as well as a large number of phase boundaries and defects. And the impedance matching between material and free space was attributed to the effective regulation on electromagnetic parameters of the initial system composition. Moreover, the solid phase combination reaction among Na₂O, Al₂O₃ and SiO₂ could weaken the strong alkalinity caused by RM.