The Bayer Process-The Main Production Method of Alumina
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Author : TRUNNANO
Update time : 2020-11-10 08:45:07
Alumina is a stable oxide of aluminum and is also called bauxite in mining, ceramics and material sciences. With the rapid development of our country's electrolytic aluminum, ceramics, medicine, electronics, machinery and other industries, the market still has a large room for growth in demand for alumina, and alumina output will continue to grow.
There are many methods for extracting alumina from ore, such as the Bayer method, soda-lime sintering method, Bayer-sintering combined method, etc. The Bayer Process has always been the main method for producing alumina, and its output accounts for about 95% of the world's total alumina output. Since the 1970s, the acid method has made great progress, but it has not been applied in industry.
The development of producing alumina products by Bayer process
It was invented in 1888 by Austrian Bayer (K.J.Bayer). The principle is to use caustic soda (NaOH) solution to warm and dissolve alumina in bauxite to obtain sodium aluminate solution. After the solution is separated from the residue (red mud), the temperature is lowered, and aluminum hydroxide is added as a seed crystal. After a long time of stirring, the sodium aluminate is separated into aluminum hydroxide, washed, and calcined at a temperature of 950～1200℃. Obtained alumina products. The solution after precipitation of aluminum hydroxide is called mother liquor, which is recycled after evaporation and concentration.
Due to the different crystalline structures of gibbsite, boehmite and diaspore, their solubility in caustic soda solution is very different, so different dissolution conditions should be provided, mainly different dissolution temperatures. The gibbsite type bauxite can be dissolved at 125～140℃, and the diaspore type bauxite should be dissolved at 240～260℃ and lime (3～7%) is added.
The advantages of producing alumina products by Bayer process
The main progress of the modern Bayer Process lies in:
1. Large-scale equipment and continuous operation; 2. Automation of the production process; 3. Energy saving, such as high-pressure enhanced dissolution and fluidized roasting; 4. Production of sandy alumina to meet aluminum electrolysis and flue gas The need for dry purification.The advantages of the Bayer
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 theBayer Process, SiO2 is transformed into sodalite-type hydrated sodium aluminosilicate (Na2O·Al2O3·1.7SiO2·nH2O), which is discharged along with the red mud. Every kilogram of SiO2 in the ore will cause about 1 kilogram of Al2O3 and 0.8 kilograms of NaOH. The lower the aluminum-silicon ratio of bauxite, the worse the economic effect of the Bayer Process. Until the late 1970s, the aluminum-silicon ratio of the bauxite processed by the Bayer Process was greater than 7-8. As the resources of high-grade gibbsite-type bauxite are gradually decreasing, how to use other types of low-grade bauxite resources and new energy-saving technologies have become important research and development directions.
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