An Environmentally Friendly Method for Producing α-Fe₂O₃ Pigment from Low-Grade Hematite Residue

This study employed low-grade hematite acquired from zinc hydrometallurgy to synthesize α-Fe₂O₃ pigment via high-temperature hydrothermal treatment. This study investigated the effects of hydrothermal conditions on α-Fe₂O₃ pigment. The results indicate that hydrothermal treatment causes the internal rearrangement of Fe (oxyhydr)oxides into Fe oxides. A high-quality α-Fe₂O₃ pigment with a Fe content > 69% and Zn and S content < 0.15% and 0.25% was successfully synthesized using the HCl-H₂O medium at > 260°C. The average crystal size of α-Fe₂O₃ pigment was found to be between 45 nm and 80 nm. The α-Fe₂O₃ pigment consists of prismatic crystals with a smooth surface and distinct edges. The UV-VIS-NIR spectra demonstrated that the α-Fe₂O₃ pigment strongly absorbs light in the wavelength range of 200–420 nm, and its absorption edge falls between 420 nm and 550 nm. Additionally, the α-Fe₂O₃ pigment has chromatic values of L* = 37.27–38.69, a* = 5.07–6.26, and b* = 1.70–2.49. All α-Fe₂O₃ products show similar colors. This work introduces an environmentally friendly method for synthesis of high-quality α-Fe₂O₃ pigment using iron removal residue in zinc hydrometallurgy.