Ural Scientists Propose New Method of Bauxite Processing

12:49, September 22, 2023

This will increase alumina recovery to 98 percent and cut red sludge separation in half

The scientists of the Ural Federal University modified the Bayer technology and increased the efficiency of the extraction of aluminum oxide (alumina) from bauxite (the main raw material for the production of aluminum). With the standard processing method, the maximum alumina extraction rate was 80-85 percent. The modified technology will allow up to 95-98 percent of the substance to be extracted from the bauxite. In addition, the new processing method will reduce the amount of red mud (also known as bauxite sludge), a byproduct of the bauxite processing process. This will contribute to sustainable and environmentally friendly production. More information is available in the journal Metals. The work was supported by the Russian Science Foundation (Project No. 22-29-01515).

"For every ton of bauxite, the standard Bayer process produces 0.7 to 1 ton of red mud. This means that for every ton of bauxite we process, almost the same amount of red mud is stored in the sludge fields. Our process allows us to reduce the red mud emission to 300 kg per ton of bauxite. In addition, the alumina recovery rate increases significantly - up to 98 percent, compared to 80-85 percent for conventional processing," explains Andrei Shoppert, Associate Professor at the Department of Non-Ferrous Metallurgy at UrFU. 

Red mud is produced during the process of chemical treatment with alkaline solutions of crushed bauxite to extract alumina. The main hazard of red mud is its high alkalinity and the presence of heavy metals and other hazardous substances.

"In the Sverdlovsk region, for example, there are two alumina refineries. During their operation since the middle of the last century, more than 100 million tons of red sludge have accumulated. It can be a source of man-made disasters, as was the case in Hungary in 2010. In addition, if the sludge is too dry, its particles can be carried by the wind and pollute the environment," says Andrei Shoppert.

The Bayer process is the most commonly used method of producing alumina from bauxite. The process begins by crushing the bauxite into small fractions so that it can be more easily processed by hydrometallurgical methods. The crushed bauxite is then placed in steel reactors and mixed with an alkaline solution. After mixing and holding under pressure at 230°C for several hours, the alumina is extracted into the solution, leaving a solid residue called red mud. The resulting solution is sent to precipitate aluminum hydroxide. The aluminum hydroxide is then calcined to produce alumina powder, which can be used to produce aluminum.

To improve Bayer's technology, scientists applied the technology of electrolytic reduction of iron compounds. This increased the leaching efficiency by removing stubborn minerals containing iron along with aluminum. In addition, the amount of alumina lost along with silicon was reduced by pre-siliconizing the bauxite at 95-120°C.

The scientists will continue to work in this direction. The next experiments will focus on refining the process to ensure that no red sludge is formed by producing metallic iron during electrolysis, a process in which an electric current is used to reduce chemical compounds.

The study also involved scientists from the Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences.

Reference

Aluminum is the most abundant metal on Earth, accounting for more than 8% of the mass of the Earth's crust. It is highly resistant to corrosion and has a long service life, which is why it is actively used in industries such as aerospace, automotive, power generation, etc.

According to Fortune Business Insight, the global aluminum market was worth more than $159 billion in 2021. In 2022, China produced more than 40 million tons of the metal - more than half of the world's aluminum. India produced 4 million tons of aluminum, just ahead of Russia, which mined about 3.7 million tons. In fourth place is Canada - this country was able to extract 3 million tons of aluminum.

Sergey Lukyanchenko

The news article was translated by UrFU International Marketing Office. 
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