The two major processes of the Bayer method: decomposition and dissolution. In the process of seed decomposition of sodium aluminate solution, the molecular weight of the sodium aluminate solution is relatively low (about 1.6). At normal temperature, aluminum hydroxide is added as a seed crystal and continuously stirred, and the Al2O3 in the solution slowly precipitates out as aluminum hydroxide. At the same time, the molecular ratio of the solution continues to increase.
Preparation of a-Al2O3 fine powder and ultrafine powder and ultrafine powder are also called fine powder and ultrafine powder. With its particle size as the criterion, a-Al2O3 fine powder with a particle size of not more than 90um is generally referred to as micropowder or ultrafine powder. The particle size limits of both fine powder and ultrafine powder are not unified in various industries. The refractory industry at home and abroad generally uses 5um as the limit between the two.
For ball mill pulverization, as the ball milling time increases, the fineness of the raw material becomes finer, and the speed of thinning is faster at the initial stage and slower at the later stage. This is because the pulverized fine powder forms aggregates under the action of molecular cohesion and prevents further pulverization; at the same time, the fine powder acts as a buffer for large particles Effect, making larger unpulverized particles difficult to further pulverize.
At present, more than 90% of the alumina and aluminum hydroxide produced worldwide are produced by the Bayer process. The higher the Al2O3 content, the better the various technical indexes of smelting corundum. SiO2 is a harmful impurity in the production of alumina by the alkaline method. However, when the ball milling time is extended to a certain limit, the pulverization effect is reduced. For fine powder. The higher the content, the better.
Al2O3 is the main component in bauxite. At present, the production of industrial alumina requires an aluminum-silicon ratio of not less than 3.0 to 3.5. Other oxides are regarded as impurities. The high content of SiO2 in bauxite will reduce the production efficiency of smelting brown corundum or the production of industrial and increase the impurity component. Al2O3-H2O crystalline compounds can be prepared by artificial methods.
The quality requirements of high alumina bauxite include chemical composition, dehydration degree, particle size, etc., because these factors will affect the brown corundum smelting technical indicators and product quality to varying degrees. High alumina bauxite is the raw material to provide Al2O3, which is the main component of corundum. With the increase of Al2O3 content, the unit power consumption decreases. Therefore, the smelting of brown corundum requires the use of high-quality bauxite as much as possible.
Different types of bauxite have different crystal states due to their alumina, so the reaction ability with sodium aluminate solution will naturally be different. Even if the same type of bauxite has different crystal integrity due to different places of origin, its dissolution performance will be different. The dissolution performance of different types of bauxite will be discussed below. In gibbsite type bauxite, mainly exists in the form of gibbsite (Al2O3 · 3H2O).
As we all know, special refractories are a group of new refractories developed on the basis of traditional ceramics and refractories, also known as high temperature ceramics. Ceramic is named after technology. Usually, products made by powder making, molding, sintering and other processes are called ceramics. It can also be said that special refractories are refractory products made of ceramic production process. The slurry shall have good suspension and fluidity.
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