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Under the background of carbon peak and neutrality, the composite microwave absorbents are prepared using coal‐based solid waste fly ash (FA) as raw material, supporting the implementation of comprehensive utilization for FA and the low‐cost preparation for microwave absorbents. CoNi‐loaded FA composites (CoNi@FA) are prepared via a simple rotary evaporation and sintering process, involving the introduction of Co2+–Ni2+ into FA as well as the subsequent reduction process during which the CoNi alloy transforms from the metallic oxide. As expected, the CoNi@FA800 manifests excellent microwave absorption performance, and the minimum reflection loss (RLmin) value is −39.8 dB. The effective absorption bandwidth (EAB) is extended to 3.4 GHz when the coating thickness is 2.0 mm. These are attributed to the introduction of CoNi alloy, endowing CoNi@FA composites with proper impedance matching and attenuation characteristics. Thus, the CoNi@FA will be a potential candidate in the field of microwave absorbent, which not only realizes the resource utilization of FA efficiently, but also makes a compromise between economic and environmental benefit simultaneously. [ABSTRACT FROM AUTHOR]

To cut the cost of microwave absorption materials (MAMs) and achieve the recycling of semicoke (SC), the by‐product in coal hydrogasification process, SC was applied to prepare composite MAMs. The facile synthesis process involves liquid‐phase impregnation, and then in situ carbothermal reduction treatment. Champion sample prepared under 800 °C (FeSC800) exhibits the minimum reflection loss (RLmin) of −39.3 dB under a coating thickness of 2.5 mm, and the effective absorption bandwidth (EAB) can reach 3.9 GHz (14.1–18 GHz) at a coating thickness of 1.5 mm. The enhancement of interfacial and dipole polarization, as well as the synergistic effect between the dielectric properties of SC matrix and the magnetic properties of Fe particles, can account for the excellent microwave absorption (MA) performance. In view of the source of SC matrix, the prepared FeSC800 was not only expected to become a candidate in the field of MAMs, but also presented a promising approach for the resource utilization of SC. [ABSTRACT FROM AUTHOR]