Research On The Preparation Process Of Magnesium Hydroxide Based On Continuous Reactor

Magnesium hydroxide,as an inorganic flame retardant additive,has been widely concerned by scholars from all walks of life for its thermal stability,non-toxicity,smoke suppression and other functions,the preparation method has also become the focus of research at home and abroad.In this paper,three different crystallization devices are taken as research objects.Their effects on the preparation of magnesium hydroxide were investigated.At the same time,hydrothermal improvement was carried out on the finished magnesium hydroxide,The product performance was improved by increasing the concentration of mineralizer,increasing the hydrothermal temperature and prolonging the hydrothermal time,Determine the best process conditions.The specific surface area analyzer(BET),laser particle size analyzer,scanning electron microscope(SEM)and X-ray diffraction(XRD)were used to characterize the magnesium hydroxide products.The crystal morphology is better when the ammonia is added by dropping in a kettle reactor.Increasing aging temperature and extending aging time are beneficial to improving agglomeration.The experimental results show that:Using magnesium salt and ammonia as raw materials,magnesium hydroxide was prepared by continuous impingement flow reaction crystallization device.The product stayed in the reactor for a short time,resulting in serious particle agglomeration.Magnesium hydroxide was prepared using magnesium salt and ammonia as raw materials in an air-lift circulation reactor.When the magnesium salt concentration was0.1 mol·L^-1,the flow rate was 30 ml·min^-1,the ammonia flow rate was 269 ml·min^-1,and the reaction temperature was 90?,the average particle size of the product was18.5?m.Compared with magnesium sulfate,magnesium hydroxide prepared from magnesium nitrate has an average particle size of 9.33?m,small polarity,better dispersion,and more complete crystal surface growth.The morphology and grain size of magnesium hydroxide can be improved by increasing the hydrothermal temperature,lengthening the reaction time and using sodium hydroxide of certain concentration as mineralizer.When the concentration of mineralizer is 0.4 mol·L^-1,the hydrothermal temperature is 140?and the reaction time is 6 h,magnesium hydroxide polarity is weak,dispersion is good,and the angle is clear in six-square flakes.Under the same modification conditions,magnesium hydroxide was prepared by using magnesium nitrate as raw material.The reaction time was 3 h,and the particle size was the smallest,which was 6.01?m.The growth behavior of Mg(OH)₂crystals was simulated by molecular simulation software,and the reason of positive hexagonal shape was revealed.Examines the nitrate ion and sulfate ion to the influence of magnesium hydroxide growth habit,the result shows that compared with sulfate,nitrate ion only for each respective(001),vacuum slab model(00-1)growth surface,and reduce the size of(001),(101),(111)crystal growth rate of the slab model,main show larger surface area,thus more conducive to forming the six-party piece of magnesium hydroxide.