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.
Highlights
The main industrial approach used for alumina production is the Bayer method, which is based on the selective dissolution of bauxite ore components by alkaline solution
Leaching by alkaline solutions is unsuitable for recovery of titanium and rare-earth elements (REEs); acidic leaching leads to dissolution of iron with the valuable components, which hinders the subsequent recovery of valuable components from the solution
Direct leaching of valuable components from red mud generates a large amount of wastewater, which must be utilized and is unacceptable for the environment
Summary
The main industrial approach used for alumina production is the Bayer method, which is based on the selective dissolution of bauxite ore components by alkaline solution. This method generates a large amount of waste called red mud. Red mud is the insoluble portion of the ore that is dumped into landfills. Production of 1 ton of alumina generates from 0.9 to 1.5 tons of red mud [1,2]. Red mud landfills occupy large areas, which leads to environmental damage and increases environmental risks. Global alumina production generates more than 175.5 million tons of red mud annually [5]. Development of cost-effective technologies for red mud processing is a crucial environmental, scientific, and technical task
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