Brief introduction of aluminum fluoride production process

- Sep 11, 2020-

Brief introduction of aluminum fluoride production process

Date: September 11, 2020

Author: Vic Qin

Aluminum fluoride , Aluminum fluoride molecular formula: AlF3 molecular weight: 83.98 properties: white crystal or powder. The relative density at 25°C is 2.882. It is slightly soluble in water, acid and alkali solutions, insoluble in most organic solvents, and has greater solubility in hydrofluoric acid solutions. Anhydrous aluminum fluoride is very stable in nature; it does not react with liquid ammonia or even with concentrated sulfuric acid until it is heated to smoke. It does not change when it is eutectic with potassium hydroxide, nor is it reduced by hydrogen. It does not decompose when heated, but it sublimates. The sublimation temperature is 1291. ℃. It can be partially hydrolyzed into hydrogen fluoride and aluminum oxide by steam at 300~400℃. poisonous.

Used as a flux for ceramic outer layer glaze and enamel glaze, as a flux for non-ferrous metals. Used in welding liquid in metal welding. Used to make optical lens. It is also used as a catalyst for organic synthesis and a raw material for artificial cryolite. 


The production processes of aluminum fluoride products: 

1. Wet production process ( with water acid ): the gas produced after the high-temperature reaction of sulfuric acid and fluorite is directly absorbed into 30% to 35% of hydrofluoric acid, which is 90% with aluminum hydroxide. It is synthesized into AlF3 . 3H2O at about 90℃. After filtration, it is dehydrated and dried at high temperature, and finally aluminum fluoride AlF3 is obtained. As the water vapor generated during dehydration decomposes AlF3, the wet-process aluminum fluoride content is low, there are many impurities, the water content is high, the bulk density is low, and the fluidity is poor.  Basically it is not suitable for modern electrolyzers. Chemical indicators: F≥57%, Al≥28%, Na≤3.5%, H2O≤ 3 %.   

2. Dry production process ( crude acid ): 1. Crude acid dry method: The gas generated after high temperature reaction of sulfuric acid and fluorite enters the fluidized bed after rough washing, and reacts with dried aluminum hydroxide to generate aluminum fluoride at high temperature. Since the hydrogen fluoride content after rough washing is about 96%, the impurities are relatively high, and the impurities of aluminum fluoride products are relatively high; especially without desiliconization, the silicon dioxide content of aluminum fluoride products reaches 0.25%. These impurities will affect the quality of electrolytic aluminum and increase the power consumption during electrolysis. F≥61%, Al≥30%, Na≤0.5%, H2O≤0.5%, SiO2≤0.28%, P2O5≤0.04%, Fe2O3≤0.1%

3. Anhydrous production process (refined acid): high temperature of sulfuric acid and fluorite The gas generated after the reaction enters the evaporator after rough washing, freezing, degassing, and rectification. At this time, the content of hydrogen fluoride is generally 99.5%; the vaporized hydrogen fluoride gas (content close to 100%) enters the fluidized bed and is Aluminum hydroxide reacts to produce aluminum fluoride at high temperatures. Due to the high purity of hydrogen fluoride, the quality of aluminum fluoride produced in this way is very good, and the impurities are very low, especially the content of silicon dioxide is only 0.02%, and the content of phosphorus pentoxide is only 0.00 4 %, which is very beneficial to the production of electrolytic aluminum. F≥62%, Al≥32%, Na≤0.5%, H2O≤0.5%, SiO2≤0.03%, P2O5≤0.01%, Fe2O3≤0.03%

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