Multiphase iron oxide submicrostructures derived from steel swarf: Synthesis and structural characterization

In this study, iron oxide submicroparticles were synthesized via an alkaline co-precipitation method using steel waste (swarf) as a source of Fe²⁺ and Fe³ ⁺ precursors, containing minor impurities such as minor impurities such as Mn, Cu and Cr, following a circular economy approach. These residues are typically generated during steel pickling and polishing processes and are commonly discarded in landfills despite their high Fe content (>60 wt%). Their recovery reduces environmental impact and supports waste valorization strategies. The as obtained particles were stabilized with citric acid or PEG-PPG-PEG surfactants and characterized using X-ray fluorescence (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. XRF confirmed iron as the predominant component, with minor traces of Mn and Cr. Rietveld refinement of XRD patterns revealed a multiphase composition dominated by magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃), with a minor fraction of hematite (α-Fe₂O₃). Raman spectra were acquired using a sing a 785 nm excitation laser, optimized to minimize thermal and fluorescence effects. Gaussian deconvolution of A₁g, T₂g, and E g modes enabled clear discrimination among the iron oxide phases. This work supports the sustainable valorization and recycling of steel waste as a precursor for magnetic submicroparticles materials.