The Bayer Process-The Main Production Method of Alumina

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Alumina Bauxite is also known as a stable aluminium oxide in the fields of mining, ceramics and materials sciences. The rapid development of our country’s electrolytic aluminium, ceramics industries, medicine, electronics and machinery will increase the demand for alumina.
There are many ways to extract alumina from ore. These include the Bayer method and other methods such as soda-lime sintering. The Bayer Process was the primary method for producing aluminum, with its output accounting for approximately 95% of total global alumina output. Although the acid method made huge progress in the 1970s it was not used by industry.

Bayer Process: A new way to produce alumina

The Austrian Bayer K.J.Bayer invented it in 1888. The principle is that caustic (NaOH solution) is used to warm alumina and dissolve it in 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, the sodium-aluminate solution is separated to aluminum hydroxide. Then, it’s washed off and calcined in a temperature range of 950-1200. The alumina is obtained. Mother liquor is the solution that remains after precipitation.

Because gibbsite and diaspore are different in their crystalline structure, they will dissolve at different temperatures. The gibbsite-type bauxite dissolves at temperatures between 125 and 140, and diaspore-type bauxite at 240260 with the addition of lime (37%).

Bayer process alumina: advantages and disadvantages

The Bayer Process is a modern process that has been characterized by:

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. Dry purification of flue gases and aluminum electrolysis is needed for production of sandy alumina. 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 ration of bauxite. The Bayer Process produced bauxite with an aluminum-silicon proportion greater than 8 until the late 70s. In order to make the most of the diminishing resources of gibbsite bauxite, research and development has focused on finding new ways to save energy and using other types of bauxite.

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