Preparation of magnesium hydroxide by ammonia gas method

Magnesium hydroxide of high mass fraction slurry was directly synthesized without any additives,using bischofite and ammonia as raw materials. Stirring speed,mole ratio of ammonia to magnesium,ammonia gas addition rate,ageing time reaction temperature and magnesium chloride concentration were studied to find their influences to magnesium hydroxide slurry concentration and particle size. The optimum processing conditions were obtained as follows: stirring speed 350 r /min,mole ratio of ammonia to magnesium 2∶ 1,ammonia addition rate 320mL /min,aging time 90 min,reaction temperature 60 ℃ and magnesium chloride concentration 4. 30 mol /L. The effects of characterize product morphologies,structures and size distributions involved were studied through scanning electron microscope,X-ray diffractometer and laser particle analyzer. The magnesium hydroxide obtained under the optimal reaction conditions had D50of 1. 43 μm,D90of 2. 40 μm,purity of 99. 60% and whiteness of99. 34. The reaction yield reached 69. 41% with magnesium hydroxide slurry mass fraction of 12. 26%.