An eco-friendly process of high-temperature calcification transformation process for sustainable alumina production from gibbsitic bauxite

The Bayer process, currently the predominant method for global alumina production, generates substantial quantities of highly alkaline red mud during production. Due to the absence of appropriate, cost-effective, large-scale disposal methods, the majority of red mud is managed through stockpiling, which poses a significant threat to the ecological environment because of its highly alkaline nature. In this study, a high-temperature calcification method based on source interception was employed to treat gibbsitic bauxite with a focus on mineral phase reconstruction. This method not only enabled efficient high-temperature alumina dissolution but also resulted in a new type red mud structure with a very low alkali content. A systematic investigation was carried out on the thermodynamics of the calcification process as well as the influence of process parameters on this transformation. The chemical composition, mineral phase, and microstructure of the bauxite and slag during different stages of the calcification process were analyzed using X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results showed that temperature and the calcium-to-silicon (C/S) molar ratio had a significant impact on the calcification process. Under high-temperature conditions, adding an appropriate amount of calcium oxide promoted alumina dissolution and sodium oxide recovery. The non-isothermal phase transformation and kinetics of the calcification process were examined through HP DSC. With a calcification temperature of 260 °C, a C/S ratio of 2.5, a mother liquor concentration of 240 g L⁻¹, a caustic ratio of 3.1, and a reaction time of 60 min, the dissolution rate of alumina in bauxite reached 88.63%, which is a 10% improvement compared to the low-temperature Bayer process. The content of Na₂O and the aluminum-to-silicon ratio in the calcined slag were 0.71% and 1.42, respectively. The new type red mud, rich in iron oxide and with a low content of Na₂O, can be mixed with an appropriate amount of iron concentrate and binder to produce iron ore pellets. This enables the full utilization of the new red mud and promotes the clean production of alumina.