球形氢氧化镁的制备及其晶体生长动力学

A kinetics study on growth process of Mg(OH)_2 crystal

制备花状球形氢氧化镁粉体,研究了几种关键因素对镁回收率的影响和氢氧化镁的晶体生长动力学.结果表明,随着反应溶液中Mg^(2+)初始浓度和pH值的提高,镁的回收率提高;提高反应温度使镁的回收率提高,但当温度超过60℃后,反应溶液中氨的大量挥发使其pH值迅速降低,因而镁回收率下降;陈化可以提高镁的回收率,当陈化时间超过60 min后因镁已完全沉淀,回收率不再提高.在最佳工艺条件下用氨法制备的氢氧化镁颗粒为花状球形,形状规则,分散性好,粒度均匀,粒径约2μm,单片厚度约30 nm.晶体生长动力学研究表明,析出Mg(OH)_2晶体的质量和Mg(OH)_2晶粒平均粒径随着时间呈指数增长.

ABSTRACT Flower-like spherical Mg（OH）2 powder was prepared. The effects of several key factors on recovery rate of Mg and the crystal growth kinetics of Mg（OH）2 were studied. The results show that with the increasing of initial concentration of Mg^2＋ and pH value, the recovery rate of Mg increases; increase the reaction temperature, the recovery rate increases, but when the temperature is above 60 ℃, the pH value of reaction system decreases rapidly due to the volatilization of ammonia, and the recovery rate decreases; ageing process can increase the recovery rate of Mg, when the ageing time is above 60 rain, because Mg has been precipitated completely, the recovery rate increases no more. Mg（OH）2 grains prepared by ammonia precipitation method under prime conditions are flower-like spherical, the shape is regular, the dispersivity is good, the granularity is uniform, the grain size is about 2 μm, the thickness of flake is about 30 nm. The mass of Mg（OH）2 precipitated and the average diameters of Mg（OH）2 grains increase exponentially with the reaction time.