Extraction of Valuable Elements from Red Mud with a Focus on Using Liquid Media—A Review

Abstract

Bauxite residue, known as red mud, is a by-product of alumina production using the Bayer process. Currently, its total global storage amounts to over 4.6 billion tons, including about 600 million tons in Russia. The total global storage of red mud occupies large areas, leading to environmental damage and increasing environmental risks. Moreover, it contains a significant amount of sodium, which is easily soluble in subsoil water; therefore, a sustainable approach for comprehensive recycling of red mud is necessary. The bauxite residue contains valuable elements, such as aluminum, titanium, and scandium, which can be recovered using liquid media. In recent years, many methods of recovery of these elements from this waste have been proposed. This paper provides a critical review of hydrometallurgical, solvometallurgical, and complex methods for the recovery of valuable components from red mud, namely, aluminum, titanium, sodium, and rare and rare-earth elements. These methods include leaching using alkaline or acid solutions, ionic liquids, and biological organisms, in addition to red mud leaching solutions by extraction and sorption methods. Advantages and disadvantages of these processes in terms of their environmental impact are discussed.

Selective Scandium (Sc) Extraction from Bauxite Residue (Red Mud) Obtained by Alkali Fusion-Leaching Method

“…Despite the method of bauxite processing, RM contains a high number of valuable components, especially rare earth elements (REEs) that are widely used in high-tech materials production [12][13][14]. REEs do not dissolve during bauxite alkali leaching and concentrate in the solid residue with an enrichment factor of about two [15,16]. Main studies on the REEs extraction from RM are devoted to scandium (Sc) extraction [3,6,9,15].…”

Leaching of Ca-Rich Slags Produced from Reductive Smelting of Bauxite Residue with Na2CO3 Solutions for Alumina Extraction: Lab and Pilot Scale Experiments

“…Supersaturation of the solution in relation to the metastable calcium aluminate hydrates is not reached in the first stages of leaching due to the continuous reaction of the Ca+ and CO 3 2− ions. At the same time, CaCO 3 is precipitated, both through solution, according to Equation (13), and on the surface of the slag particles, according to an action resembling the one described by Equation (15). The latter is the one that is progressively hindering further dissolution and is discussed next.…”

“…The leaching solution, having a considerable concentration in CO 3 2− , will aid the dissolution process by consuming the Ca 2+ ion initially dissolved, according to Equation (13) and consequently push the equilibrium of Equation (12) to the right.…”

“…(aq) + CO 2− 3 (aq) → CaCO 3(s) (13) According to Equation (13), by continuously reducing the concentration of Ca 2+ ions in solution, the solution is not allowed to reach supersaturation with respect to the metastable hydrates, at least in the initial stages of leaching, when the concentration of CO 3 2− ions is at its highest value. At the same time, as CO 3 2− ions are removed by the formation of CaCO 3 , the amount of free Na + ions increases, causticizing the solution.…”

“…Processing options include, either the direct processing of BR, or processing of intermediate phases produced by prior treatment, as is the case of slags produced after the reductive smelting of BR described earlier. The various process alternatives have been reviewed multiple times [12][13][14]. Relevant to the process under investigation is the work by B. Friedrich and F.M.…”