Preparation of Fe3O4 particles with unique structures from nickel slag for enhancing microwave absorption properties

Abstract Recycling valuable metal elements from metallurgical slags and exploring their functional material applications have attracted more recent attention. In this paper, Fe3O4 particles with unique structures, solid solutions of Mg, Ni, and Co and inlays of silicates in magnetite crystals were extracted from nickel slag by molten oxidation and magnetic separation processes. The microstructure, morphology, magnetic and electromagnetic properties, and microwave absorption performance of the Fe3O4 particles were characterized. The results show that the Fe3O4 crystals oxidized at 1400 °C exhibit granular shapes with a uniform distribution in the silicate matrix, while they change into both dendritic and granular morphology at 1450 °C and finally into dendritic structures at 1500 °C. The Fe3O4 particles prepared at 1400 °C reach an optimal reflection loss value of −29.90 dB under a thickness of 3.5 mm and an effective absorbing frequency band of 3.28 GHz (5.52–8.80 GHz), indicating that their unique structure favours microwave absorption. The joint action of strong magnetic loss and the appropriate dielectric loss were supposed to sustain the absorption mechanism of the Fe3O4 particles.