Preparation Of Spherical And Flake Calcium Carbonate By High-gravity

As an additive and reinforcing agent,calcium carbonate is widely used in papermaking,plastics,food,medicine and chemical industry and other fields.The particle size,crystal form and morphology of Calcium carbonate are vital in the performance and its end use.Therefore,the efficiently production of Calcium carbonate with regular morphology,uniform particle size and crystal form has become the focus of the industrial research.The traditional preparation methods include coprecipitation method and carbonization method,among which coprecipitation method has the defects of complex technology and high cost;The carbonization method has some disadvantages such as long reaction time and difficult morphology regulation.Therefore,in this paper,the technological conditions for the preparation of spherical and flake calcium carbonate were explored and optimized by high-gravity reaction crystallization method.Two kinds of calcium carbonate with different shapes,spherical and flake,were successfully prepared by high-gravity reaction crystallization method using high concentration calcium hydroxide slurry as raw material and using different crystal control agents.The conditions of crystallization and ball formation by high-gravity reaction were optimized and the ball formation mechanism was discussed.At the same time,L-glutamic acid,ammonium chloride and ethanol remaining in the solution after carbonization reaction were reused,which reduced the production cost of calcium carbonate.The main research contents are as follows.The spherical calcium carbonate was prepared with Calcium hydroxide slurry and Carbon dioxide as raw materials,in the high gravity rotating packed bed with ammonium chloride and L-glutamic acid as crystal form control agent.The effects of slurry concentration of calcium hydroxide,carbon dioxide flow rate,dosage of crystalline controller,high-gravity speed,carbonation temperature and liquid flow rate on the morphology of spherical calcium carbonate were investigated.The results showed that the total feeding amount of calcium hydroxide slurry was 1L,the initial concentration of calcium hydroxide slurry was8%,the gas flow rate of carbon dioxide was 0.4Nm~3/h,the addition amount of L-glutamic acid was 4wt%,the addition amount of ammonium chloride was 20wt%,the high-gravity speed was 1200 r/min,the carbonization temperature was 25℃and the liquid flow rate was 400L/h.vaterite type spherical calcium carbonate with the particle size of about 500 nm can be obtained.And through infrared characterization,it was observed that after the reaction,part of L-glutamic acid existed in spherical calcium carbonate.The flake Calcium carbonate was prepared by changing the solvent system,and the effects of Calcium hydroxide slurry、carbonization temperature、Carbon dioxide flow rate、Liquid flow、high-gravity speed and volume ratio of ethanol to water on the morphology of flake calcium carbonate were investigated.The results showed that when the slurry concentration was 1%,the carbonization temperature was 15℃,the gas flow rate was 0.5 Nm~3/h,the liquid flow rate was300L/h,the ultra-gravity speed was 1000 r/min and the volume ratio of ethanol to water was 1.5:1,the more uniform flaky calcium carbonate can be obtained.It was also observed by X-ray powder diffractometer(XRD)that with the continuous increase of ethanol content,the content of aragonite in pellets of calcium carbonate products increased continuously,a and the highest content is74.56%.More ammonium chloride and ethanol were used in the preparation of calcium carbonate,For the centrifuged separation liquid after carbonization reaction,after recycling and adding 2wt%L-glutamic acid and a small amount of ethanol for repeated experiments,The spherical and flake calcium carbonate with relatively regular morphology can be obtained,It is proved that some reaction materials still exist in the solution after carbonization reaction.By using centrifugal liquid,the material in the solution was reused,and the production cost was further saved.