The composition, recycling and utilisation of Bayer red mud

Red mud or bauxite residue is a solid waste generated from the Bayer process. The disposal of red mud leads to a serious environmental threat because of its tiny particle size and high alkaline value. The utilisation and recycling of red mud is currently a crucial issue and needs to be addressed as soon as possible. This study demonstrates the different methods and techniques recently analysed or suggested for the consumption of bulk red mud to maintain a sustainable environment. The potential utilisations of red mud include valuable metal recovery, the preparation of construction materials and as an alternative catalyst for diverse processes, including hydrodechlorination, hydrogenation and hydrocarbon oxidation. In addition, the red mud can also be used to control environmental pollution, such as in wastewater treatment, soil remediation and the purification of flue gas. However, the proper utilisation and recycling of red mud has a number of shortcomings: pyro-metallurgical recovery involves high energy costs; large volumes of acid by-product needing to be neutralised after the leaching process; the fine particle size of red mud; and the necessity of pre-treatment in some methods. Although many studies have investigated the potential utilisation of red mud, most of them have concentrated on lab-scale studies. Therefore, a large-scale investigation of the recycling and utilisation of red mud needs to be explored. Moreover, an appropriate cost-benefit analysis of the existing technologies needs to be examined in the future because of the high cost of the transportation of a large amount of red mud from alumina refineries to the point of application.