Alumina
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 many ways to extract alumina from ores, such as using the Bayer method or combining Bayer and sintering. The Bayer Process was the primary method for producing aluminum, with its output accounting for approximately 95% of 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 soda solution (NaOH) is used to heat and dissolve alumina into bauxite in order to obtain sodium-aluminate solutions. 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 9501200. The alumina is obtained. Mother liquor is the solution that remains after precipitation.
Because gibbsite and boehmite are different in their crystalline structure, they will dissolve at different temperatures. Gibbsite-type bauxite dissolves at temperatures between 125140°C and diaspore-type bauxite at 240260°C. Lime (37%) should also be added.
Bayer Process Alumina Products: Benefits
The Bayer Process is a modern process that has been characterized by:
1. Equipment of a 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 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 ore contains about 1 kg of SiO2, which will result in 0.8 kg of NaOH and 1 kilogram Al2O3. The Bayer process has a worse economic impact the lower the aluminum-silicon bauxite ratio. Up until the late 70s, the Bayer Process used a bauxite with an aluminum-silicon ratio greater than 7. In order to make the most of the diminishing resources of high grade gibbsite bauxite, research and development has focused on finding new ways to save energy and using other types of low quality bauxite.
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Aluminum Oxide
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