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Due to different conditions, each factory may adopt slightly different process flows, but in principle, they do not have essential differences. The basic production process of Bayer process is roughly divided into the following main processes:
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Raw ore preparation is the first process of alumina production. The so-called raw slurry preparation refers to the cultivation of raw materials used in the Bayer process to produce alumina, such as bauxite, lime, sodium aluminate solution, etc., in a certain proportion to produce raw slurry with chemical composition and physical properties that meet the dissolution requirements. The requirements for the preparation of raw mineral slurry are:
① The materials involved in chemical reactions must have a certain degree of fineness
② The substances involved in chemical reactions must have a certain ratio and be evenly mixed
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Therefore, the preparation of raw ore slurry plays an important role in the production of alumina. The ability to prepare slurry that meets the requirements of alumina production will directly affect the dissolution of alumina, affecting economic and technical indicators such as red mud settling performance, seed decomposition rate, and alumina production.
Dissolution is one of the two main processes in the Bayer process for producing alumina. The purpose of dissolution is to dissolve the alumina hydrate in bauxite into a sodium aluminate solution. The dissolution effect directly affects the economic and technical indicators of Bayer process for producing alumina.
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French single tube preheating - high-pressure kettle dissolution process diagram
The leaching process mainly depends on the chemical composition and mineral composition type of bauxite. The main technical conditions and economic indicators include: dissolution temperature, dissolution time, alumina dissolution rate, alkali consumption, etc.
The so-called red mud is the mud residue obtained by dissolving bauxite, which often contains a large amount of iron oxide and is red in color. It is commonly referred to as red mud. The purpose of diluting dissolved mineral slurry is as follows:
Dissolved slurry is composed of sodium aluminate solution and red mud, and is the product of the reaction between bauxite and sodium aluminate solution at high temperature. After the dissolution process is completed, in order to proceed with the subsequent decomposition process, the stability of the dissolved slurry should not be too large, otherwise it is not convenient for the decomposition process to proceed. In order to promote the decomposition of sodium aluminate solution, it is necessary to dilute the dissolved slurry.
Due to the need for red mud sedimentation and separation of the dissolved ore slurry, diluting the dissolved ore slurry can reduce the viscosity of sodium aluminate solution and facilitate the sedimentation and separation of red mud.
Seed decomposition is the process of cooling the sodium aluminate solution, increasing its supersaturation, and then adding aluminum hydroxide as the seed and stirring to precipitate aluminum hydroxide. It is one of the key steps in the Bayer process for producing alumina. In addition to obtaining aluminum hydroxide through crystal seed decomposition, a highly caustic seed fraction mother liquor is also obtained, which serves as a circulating mother liquor for leaching bauxite, thus forming a closed loop cycle for Bayer method production of alumina.
The main technical indicators of the seed separation process include alumina concentration, molecular ratio, initial temperature, final temperature, seed ratio, decomposition time, etc. The technical and economic indicators to measure the efficiency of the seed separation process are the seed decomposition rate, unit production capacity of the decomposition tank, and the quality of the obtained Al (OH) 3. The physical properties required for sandy alumina mainly depend on the control of the seed separation process.
The aluminum hydroxide slurry obtained after seed decomposition needs to be separated to obtain the required aluminum hydroxide and seed mother liquor. Most of the aluminum hydroxide obtained after separation is returned to the process as seed crystals without washing, while the rest is washed and recycled to form the finished aluminum hydroxide product. The seed denominator solution is returned to the process for reuse.
In order to achieve the separation of aluminum hydroxide and mother liquor, different methods can be used, such as sedimentation or filtration. For slurries with a large liquid-solid ratio, sedimentation method can be used, while for slurries with a small liquid-solid ratio, filtration can be used. Due to the influence of the solid-liquid ratio of the slurry on the filtration efficiency, in general, aluminum hydroxide is first concentrated before filtration and separation.
The main technical and economic indicators include: aluminum hydroxide washing water volume, slurry solid ratio, finished aluminum hydroxide water content, filter capacity, etc.
Calcination is the process of removing attached and crystalline water from aluminum hydroxide at high temperature, and transforming its crystal form to produce alumina that meets the requirements of electrolysis. So many physical properties of alumina, especially specific surface area, resting angle, density, etc., are mainly determined by the calcination conditions.
The quality indicators of calcined products include chemical purity, reduction, particle size, and angle of repose. The technical and economic indicators of the calcination process include: calcination temperature, fuel consumption, yield, etc. (reprinted in this article)
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