Ding-Zheng Wang, Jie Yang, Jin-Lin Yang, Shao-Jian Ma, Jin-Peng Feng, Wei Mo
Bayer red mud, which is a major byproduct of the alumina industry, has attracted global attention owing to its high alkalinity and associated environmental risks. Primarily composed of iron, aluminum, and silicon oxides, along with sodium minerals, Bayer red mud exhibits alkalinity due to the hydrolysis of residual NaOH and sodium silicates. Therefore, prolonged accumulation of red mud may deteriorate soil, water, and air quality. Existing dealkalization technologies and resource utilization strategies for red mud are reviewed. Dealkalized red mud is utilized in the production of construction materials, ceramics, catalysts, and environmental remediation. Existing dealkalization approaches include acid-base neutralization, acid-gas neutralization, and precipitation. Although these methods effectively remove soluble alkalis, their efficiency against structural alkalis is limited. In particular, despite high removal efficiency, acid neutralization generates high-salinity wastewater. Besides, acid gas neutralization integrates carbon capture or flue gas desulfurization but poses scalability challenges due to secondary pollution risks. Finally, precipitation methods are environmentally friendly but achieve lower removal rates. The limitations of these dealkalization methods for Bayer red mud and challenges such as material stability, economic viability, and regional compositional variability hinder the broader adoption of the substance. Therefore, strategies involving multi-technology integration, eco-friendly dealkalization agents, or high-value iron oxide must be explored to realize optimal dealkalization. Furthermore, artificial intelligence for real-time monitoring and life cycle assessment can be employed to determine carbon footprints. Moreover, promoting closed-loop systems can facilitate the alumina industry's transition toward a circular economy.
