Abstract:

Crystallization under normal pressure is usually adopted when producing aluminum fluoride by wet method,which suffers from disadvantages such as high crystal water content in product,long crystallization time and low production capacity.Therefore,the aluminum fluoride pressurized crystallization technology was studied and the effects of the factors,such as crystallization pressure,crystallization time,addition amount of crystal seeds and filling temperature on the aluminum fluoride crystal water content were investigated.Optimized process and conditions:Put fluorosicilic acid（FSA） solution into reaction tank,heated up to 70~80 ℃;Added aluminum hydroxide based on the amount-of-substance ratio of FSA to aluminum hydroxide being 1.1:1,and reacted under 95~105 ℃ for 30 min;Filtered to obtain aluminum fluoride solution and silica gel precipitation;Shifted aluminum fluoride solution into high-pressure crystallization reactor,and added 15%（mass fraction） crystal seeds of aluminum fluoride;Maintained inner temperature 170 ℃ and crystallization pressure 0.7 MPa,crystallization lasted for 3 h;Droped the inner temperature to 80~90 ℃,vacuum filtrated the slurry after crystallization,and obtained aluminum fluoride paste after washing;Dried the obtained aluminum fluoride paste under 120~180 ℃ to remove adhering water;Raised temperature gradually to 400~600 ℃ and removed crystal water from product by calcination.The final product of aluminum fluoride was obtained after cooling.The experiment results showed that adoption of pressurized crystallization technology in producing aluminum fluoride can not only reduce both crystal water content in product and cost,improve quality and output,but also solve the bottleneck problem that restricts the development of the phosphorus chemical industry,fluorine chemical industry and electrolytic aluminum industry.

Key words: aluminum fluoride, pressurized crystallization, crystallization under normal pressure