There are many ways to extract alumina from ores, such as using the Bayer method or the combined Bayer and 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 ) 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 precipitation.
Because gibbsite and boehmite are different in their crystalline structure, they will dissolve at different temperatures. The gibbsite-type bauxite dissolves at temperatures between 125140 and the diaspore-type bauxite at 240260, with a lime additive of 37%.
Bayer Process Alumina Products: Benefits
The Bayer Process is a modern process that has mainly advanced in:
1. Equipment of large scale and continuous operation
2. Automation of production processes;
3. Saving energy by using fluidized roasting, high-pressure enhanced disolution or other methods of 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. Before the late 1970s the aluminum-silicon ration of bauxite treated by the Bayer Process had been greater than 7. 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 low grade bauxite.
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