Alumina recovery from bauxite residue: A concise review

Aluminum demand has increased with modernization of our society. As the primary source of aluminum is bauxite ore, this has resulted in more accumulation of bauxite residue. A bauxite residue typically contains 15-25% of alumina depending on the origin of its ore and process conditions. Along with alumina, it also contains iron, titanium and rare earth elements (REEs) in considerable levels. There is still little effort for commercial use of bauxite residue with few exceptions like in cement production such as in India and China. However, high levels of soda and iron oxides in the residue can limit such applications too. For complete valorization of bauxite residue, iron content needs to be lowered by recovering it through smelting reduction followed by slag leaching for the recovery of other metals (e.g., Ti and REEs). Smelting reduction process becomes uneconomical with high alumina as it hinders efficient separation of metal and slag phases. One of the most promising options to circumvent that problem is alumina recovery before smelting to remove iron. The main focus of this paper is to give a comparative and comprehensive overview on the processes developed for aluminum recovery from bauxite residue. These processes are, namely, a second Bayer process, Pederson process, soda or soda-lime sintering, reduction alkali roasting, smelting and acid leaching, and calcification and carbonation processes.