Study on Hematite Reduction via Wheat Bran Alkaline Thermal and Its Application Potential in the Bayer Process

The Bayer process primarily focuses on the extraction of alumina, yet it insufficiently addresses the comprehensive recovery of other valuable elements, resulting in significant environmental threats due to the discharge of large quantities of red mud. By converting iron-bearing phases such as aluminum goethite, andradite, and hematite into magnetite, the dissolution efficiency of alumina can be significantly enhanced, while also achieving an efficient recovery of iron-containing resources. This study employs the theory of mineral phase reconstruction to achieve the directional transformation of hematite into magnetite by utilizing the reducing properties of wheat bran under alkaline thermal conditions. A systematic investigation was conducted to evaluate the effects of various parameters on the conversion efficiency during the alkaline thermal reduction of hematite with wheat bran, utilizing X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and chemical analysis for assessment. Furthermore, the surface characteristics of hematite, magnetite, and desilication product (DSP) were characterized in conjunction with Zeta potential, wettability, and solvation trends. The findings indicate that the conversion efficiency of hematite significantly improves with increasing temperature, wheat bran dosage, and sodium oxide concentration. Under simulated Bayer process dissolution conditions, with a sodium oxide concentration of 240 g/L, a molecular ratio of 3.1, a temperature of 270 °C, a liquid-to-solid ratio(L/S) of 4:1, and a mass ratio of wheat bran to hematite (W/H) of 0.5, the reduction rate of iron oxide reached 95.52% after 60 min of dissolution. Compared to hematite, magnetite exhibits significant differences in surface properties with DSP, which facilitates the agglomeration, growth, and dissociation of hematite from DSP during the transformation process. Moreover, the addition of wheat bran during the high-temperature Bayer digestion process of high-iron bauxite promoted the transformation and dissociation of iron-containing mineral phases, achieving hematite reduction rates and alumina recovery rates of 93.20 and 89.93%, respectively. Finally, this study proposes a novel process based on mineral phase reconstruction for the calcification and biomass treatment of high-iron bauxite, offering a new approach for the efficient recovery of iron-containing resources and the disposal of red mud in the alumina production process, thereby promoting the green and sustainable development of the alumina industry.