This study presents the utilization of mill scale waste, which has attracted much attention due to its high content of magnetite (Fe₃O₄). This work focuses on the extraction of Fe₃O₄ from mill scale waste via magnetic separation, and ball milling was used to fabricate a microwave absorber. The extracted magnetic powder was ground-milled using two different techniques: (i) a conventional milling technique (CM) and (ii) mechanical alloying (MM) process. The Fe₃O₄/CM samples were prepared by a conventional milling process using steel pot ball milling, while the Fe₃O₄/MM samples were prepared using a high-energy ball milling (HEBM) method. The effect of milling time on the structural, phase composition, and electromagnetic properties were examined using X-ray diffraction (XRD) and a vector network analyzer (VNA). XRD confirmed the formation of magnetite after both the magnetic separation and milling processes. The results revealed that Fe₃O₄ exhibited excellent microwave absorption properties because of the synergistic characteristics of its dielectric and magnetic loss. The results showed that the Fe₃O₄/CM particle powder had a greater absorption power (reflection loss: <-10 dB) with 99.9% absorption, a minimum reflection loss of -30.83 dB, and an effective bandwidth of 2.30 GHz for 2 mm thick samples. The results revealed the Fe₃O₄/MM powders had higher absorption properties, including a higher RL of -20.59 dB and a broader bandwidth of 2.43 GHz at a matching thickness of only 1 mm. The higher microwave absorption performance was attributed to the better impedance matching property caused by the porous microstructure. Furthermore, the magnetite, Fe₃O₄ showed superior microwave absorption characteristics because of the lower value of permittivity, which resulted in better impedance matching. This study presents a low-cost approach method by reutilizing mill scale waste to fabricate a high purity crystalline Fe₃O₄ with the best potential for designing magnetic nano-sized based microwave absorbers.

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