Toward sustainable green alumina production: A critical review on process discharge reduction from gibbsitic bauxite and large-scale applications of red mud

Abstract

In 2021, global alumina production reached over 135 million tons and discharged approximately 200 million tons of red mud, leading to severe environmental safety hazards. More than 70% of raw materials originated from gibbsitic bauxite. This work reviews existing and potential process from open literature to treat gibbsitic bauxite and reduce red mud discharge from the alumina production process, which are divided into two categories. The first strategy involves non-Bayer methods such as smelting reduction, reduction roasting, sub-molten salt, ammonium sulfate roasting, acid leaching, and calcification–carbonation. The current obstacle to implementing these methods is the lack of economics, making industrial application challenging. The second potential industrial application strategy is to modify the current Bayer process, with critical measures involving the enhancement digestion of inert aluminum-bearing minerals, dissociation and recovery of iron minerals, and separation of desilication products. Analyzing the reaction mechanism and process flow clarify that the modified Bayer method is more favorable to the cost-effectively and synergistic extraction of aluminum, iron, and other elements. The red mud obtained by the modified Bayer process can be efficiently utilized. Therefore, a mini-summary of the areas where red mud is expected to be substantially dissipated (e.g., the steel industry, cement building materials, and ecological restoration of red mud stockpiles) is provided. The review can advance the current technology on the comprehensive utilization of gibbsitic bauxite, especially process discharge reduction approaches and large-scale abatement ways for red mud. Our results can contribute to the future development of sustainable green alumina production.