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Bauxite is a stable aluminium oxide that is 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, including the Bayer method and combined Bayer/sintering method. 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: A new way to produce alumina
The Austrian Bayer K.J.Bayer invented it in 1888. The principle is that caustic (NaOH), a solution of sodium hydroxide, is used to warm alumina and dissolve it in bauxite. This produces sodium aluminate. After the residue is removed (red mud), temperature 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 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, while diaspore-type bauxite dissolves at 240260 with the addition of lime (3-7%)
Bayer process alumina: advantages and disadvantages
The Bayer Process is a modern process that has made major progresses in:
1. Equipment of large scale and continuous operation
2. Automating production processes;
3. Saving energy by using fluidized roasting, high-pressure enhanced disolution or other methods of dissolution.
4. Production of sand to meet 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 0.8 kg of NaOH for every kilogram of SiO2 present in the ore. The Bayer process has a worse economic impact the lower the aluminum-silicon bauxite ratio. The Bayer Process produced bauxite with an aluminum-silicon composition greater than 8 until the late 1970s. In order to make the most of the diminishing resources of high-grade gibbsite type bauxite, research and development has focused on finding new ways of using low-grade bauxite and developing energy-saving technology.
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