Abstract
Red mud is a by-product of alumina production from bauxite ore by the Bayer method, which contains considerable amounts of valuable components such as iron, aluminum, titanium, and scandium. In this study, an approach was applied to extract iron, i.e., carbothermic reduction roasting of red mud with sodium and potassium carbonates followed by magnetic separation. The thermodynamic analysis of iron and iron-free components’ behavior during carbothermic reduction was carried out by HSC Chemistry 9.98 (Outotec, Pori, Finland) and FactSage 7.1 (Thermfact, Montreal, Canada; GTT-Technologies, Herzogenrath, Germany) software. The effects of the alkaline carbonates’ addition, as well as duration and temperature of roasting on the iron metallization degree, iron grains’ size, and magnetic separation process were investigated experimentally. The best conditions for the reduction roasting were found to be as follows: 22.01% of K2CO3 addition, 1250 °C, and 180 min of duration. As a generalization of the obtained data, the mechanism of alkaline carbonates’ influence on iron grain growth was proposed.
Highlights
Alumina production by the Bayer process generates a considerable amount of highly alkaline solid waste called the bauxite residue or red mud
To study and compare the influence of Na2 CO3 and K2 CO3 additions on iron grain growth during the carbothermic reduction of red mud, and initially present sodium was removed by leaching with a lime slurry in a glass reactor at 90 ◦ C for 3 h [39]
Figure shows the influence of the roasting anddata duration on the degree for6 red mud without carbonate additions.temperature
Summary
Alumina production by the Bayer process generates a considerable amount of highly alkaline solid waste called the bauxite residue or red mud. Depending on the composition of bauxite ore and the technology used, production of one ton of alumina can generate from 0.9 to 1.5 tons of red mud [1,2]. 4.6 billion tons in 2018 [3], including about 600 million tons in Russia [4]. This waste is typically stored in special sludge dumps [5], which leads to misuse of large land areas and to an increase of the aluminum cost. Storage of bauxite residue leads to ground and surface water pollution, and, it can cause a discharge of red mud due to sludge dump destruction [7,8,9]
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