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Bauxite is an oxide of aluminum that is stable. It’s also used in ceramics, material science and mining. The rapid development of our country’s electrolytic aluminium, ceramics industries, medicine, electronics and machinery will increase the demand for alumina.
There are a number of methods to extract alumina from ores, such as Bayer, soda-lime-sintering, combined Bayer and sintering, etc. The Bayer Process was the primary method of producing aluminum, accounting for approximately 95% the total world alumina output. Although the acid method made huge progress in the 1970s it was not used by industry.
Bayer process for producing alumina
The Austrian Bayer K.J. Bayer invented it in 1888. The principle is that caustic (NaOH ) solution is used to warm and dissolve the alumina in the bauxite, resulting in sodium aluminate. After the solution (red mud) is separated, the temperature of the mixture is lowered and aluminum hydroxide added as a crystal seed. After long stirring, sodium aluminate separated into aluminum hydroxide. Then, it washed off and calcined in a temperature range of 9501200. The alumina is obtained. Mother liquor is the solution that remains after the precipitation of aluminium hydroxide. This is recycled following evaporation.
Because gibbsite and diaspore are different in their crystalline structure, they will dissolve at different temperatures. The gibbsite-type bauxite dissolves at 125140°C, while the diaspore-type bauxite dissolves at 240260°C with lime (37%).
Bayer Process Alumina Products: Benefits
The Bayer Process is a modern process that has made major progresses in:
1. Equipment of large scale and continuous operation
2. Automation of production processes;
3. Energy-saving techniques such as fluidized roasting, high-pressure enhanced disolution and high pressure enhanced dissolution;
4. Production of sandy alumina for aluminum electrolysis, and the need for flue gas purification. Bayer’s advantages
The economic effect of the Bayer Process is determined by the quality of the bauxite, mainly the SiO2 content in the ore, which is usually expressed by the aluminum-silicon ratio of the ore, that is, the weight ratio of the Al2O3 to the SiO2 content in the ore. Because in the dissolution process of the Bayer Process, SiO2 is transformed into sodalite-type hydrated sodium aluminosilicate (Na2O*Al2O3*1.7SiO2*nH2O), which is discharged along with the red mud. The Bayer Process will generate about 1 kg of Al2O3 for every kilogram of SiO2 present in the ore. This is followed by 0.8 kg of NaOH. The Bayer process has a worse economic effect the lower the aluminum-silicon bauxite ratio. The Bayer Process produced bauxite with an aluminum-silicon mixture greater than 8 until the late 1970s. In order to make the most of low-grade gibbsite bauxite and develop new energy-saving technology, research and development has been focused on how to utilize other types of low grade bauxite.
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