Efficient Production of Ferrous Sulfate from Steel Mill Scale Waste

Waste utilized for material development is increasingly under scrutiny in the pursuit of sustainability. Particularly, steel mill scale, a solid waste generated in the metallurgical industry through the oxidation of steel dowels, is a focus of study. In this investigation, X-ray diffraction (XRD) analysis identified wustite, magnetite, and hematite as crystalline phases, while X-ray fluorescence analysis revealed that iron oxides comprised 97% of the weight, with approximately 67% being elemental iron. Due to this composition, mill scale served as a precursor for ferrous sulfate heptahydrate (FeSO₄·7H₂O) via a process involving sulfuric acid aqueous solution leaching, ethanol filtration, and a final crystallization step. A factorial experimental design was employed to optimize the production of FeSO₄·7H₂O, assessing the influence of each variable parameter (reagents) and their interactions. Finally, the potential of mill scale in the production of FeSO₄·7H₂O, process efficiency, and quality of the resulting material were evaluated. Compared to a sample of commercial FeSO₄·7H₂O, the obtained material exhibited higher peak intensity in XRD, increased purity (reaching 99.83%), and similar thermal behavior in both differential thermal analysis and thermogravimetry. The yield of the FeSO₄·7H₂O production process from mill scale exceeded 70%.