Elementary Research On Preparation Process Of Rod-like Magnesium Hydroxide By Salt Lake Brine

Rod-like magnesium hydroxide with low surface energy, good mechanical strength, high elastic modulus and other properties, is applied to a high-end electronic products, efficient flame retardant, filler functional materials. In this paper, basic magnesium chloride precursor was prepared by salt lake brine and then the precursor was converted into rod-like magnesium hydroxide.The basic magnesium chloride precursor was prepared in three ways. Studies show that it is unavailable basic magnesium chloride with brine as raw material directly. After the boron in brine was separated from magnesium and lithium with sulfate acid and ion exchange resin, it can get basic magnesium chloride with inferior crystallization property and low purity. On the contrary, using bischofite as materal, it can gain the basic magnesium chloride precursor with good crystallization property and high purity.In the process of brine concentration and crystallization of bischofite products, The results shown that the higher the proportion of brine evaporation was, the greater the yield was. But evaporation ratio should not exceed1.44. The purity is up to above98%after recrystallization.Using bischofite as raw material, basic magnesium chloride precursor was prepared by ammonia, then the precursor was converted into rod-like magnesium hydroxide with caustic soda. The molar ratio of Mg2+and NH3·H2O, concentration of MgCl2, reaction temperature and reaction time, aging temperature and aging time have a great influence on the crystalline property of basic magnesium chloride. The results show the basic magnesium chloride can be achieved only when Mg2+concentration was3.5mol/L. when the concentration of Mg2+was less than3mol/L, only obtained magnesium hydroxide; when the concentration of Mg+was3mol/L, the products was a mixture of magnesium hydroxide and basic magnesium chloride; Further increased concentration of Mg2+, the product of diffraction peak changed broaden; reaction temperature should not exceed50℃, if not only get magnesium hydroxide; With increasing reaction time, precursor was easily converted into magnesium hydroxide; But with the longer aging time, it make the crystalline structure perfection and the particle surface become more smooth and regular, the ratio of length to diameter increased from8to50. The crystal growth of basic magnesium chloride was fitted by the common mechanism of crystal growth model. The experimental results shown when the aging temperature were30℃,40℃,50℃, it was that linear control crystal growth on the surface of the kinetic equation, which as follows:The aging temperatureThe aging temperatureThe aging temperatureIn the process of the basic magnesium chloride conversion into magnesium hydroxide, the effects of sodium hydroxide dosage, solvent composition and reaction temperature and time on the morphology of magnesium hydroxide were discussed. The results show that when the molar ratio of sodium hydroxide and basic magnesium chloride was more than2:1, the transformation can be completely and only to maintain a relatively low concentration of precursor, rod-like magnesium hydroxide particles get regular; Solvent composition has a great influence on the morphology of magnesium hydroxide. In pure water system, magnesium hydroxide appeared serious agglomeration, on the contrary, in the alcohol system, the magnesium hydroxide has good dispersion, smooth surface and high yield. The research result of basic magnesium chloride conversion into magnesium hydroxide shown that Cl" in precursor was replaced of hydroxide ion step by step, rather than basic magnesium chloride dissolution-recrystallization.The rod-like magnesium hydroxide were obtained with the alcohool solvent by adding NaOH solution at60℃, which its length-diameter ratio can reach more than35.6and purity can reach99.8%, which fits requirements and application scope.