What Is the Bayer Process?

The Bayer process is a chemical process widely used in the industry to produce alumina from bauxite. Invented by Austrian engineer Karl Joseph Bayer in 1887, the basic principle is to convert aluminum hydroxide to sodium aluminate with concentrated sodium hydroxide solution, and to re-precipitate aluminum hydroxide by diluting and adding aluminum hydroxide seeds. The sodium hydroxide solution was reused to process the next batch of bauxite to achieve continuous production. Today, 95% of the world's aluminum companies use the Bayer process to produce alumina. ^[1]

The so-called Bayer method is because it is KJ

After more than a hundred years of development, the Bayer Process has made great progress in production equipment and automation control, but its basic process principles have not changed.

The basic principle of the Bayer method is to make the following reactions alternate in different directions under different conditions:

In the formula, when the gibbsite and gibbsite are dissolved, x is 1 and 3 respectively; when the sodium aluminate solution is decomposed, x is 3.

First, the bauxite is dissolved out with NaOH solution under high temperature and high pressure conditions, and the alumina hydrate in it is reacted to the right according to the above formula to obtain a sodium aluminate solution, and impurities such as iron and silicon enter the red mud; After the mud is added to the sodium aluminate solution, it is decomposed under conditions of constant stirring and gradually cooling, so that the above formula reacts to the left to precipitate aluminum hydroxide, and a mother liquor containing a large amount of sodium hydroxide is obtained; the mother liquor is concentrated by evaporation and then Returned for dissolution of a new batch of bauxite; aluminum hydroxide is roasted and dehydrated to obtain the product alumina. ^[2]

The first process of the Bayer process is to use a pulverizer to crush the bauxite ore into particles with a diameter of about 30 mm, and then rinse the surface of the particles with water.

The Bayer process has been used in the production of alumina for more than 100 years, and has been greatly developed and improved for decades, but it still uses this name. At present, this method is still the main method of producing alumina in the world. The Bayer process is used to process low-silica bauxite (generally requires A / S> 8), especially when it is used to process gibbsite bauxite, which has the advantages of simple process, convenient operation, low energy consumption, and good product quality. . Except for some regions restricted by raw material conditions, most alumina plants now use the Bayer process to produce alumina. The Bayer process is more demanding in the treatment of diaspore bauxite. The main disadvantage of the Bayer process is that it cannot handle ore with high silica content alone. In addition, the Bayer process is difficult to process red mud.

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In 1855 the French chemist Louis Le Chatelle first proposed

The economic benefits of the Bayer process are determined by several points. One is the proportion of gibbsite contained in bauxite. The more gibbsite is contained, the smaller the energy consumption; The Bayer process converts silica to hydrated sodium aluminosilicate, which loses alumina and sodium hydroxide in the process. As the bauxite reserves with high aluminosilicon content are gradually scarce, the alumina lost in this process Sodium hydroxide and sodium hydroxide have also gradually increased, and existing researchers and companies have proposed an improvement scheme of the Bayer method combined with the sintering method. In addition, the Bayer method will cause part of the sodium hydroxide to enter the red mud, which brings strong corrosiveness to the red mud. Its pH is as high as 11-12, which brings serious environmental problems. ^[1]