盐湖水氯镁石合成三方硼镁石的结晶机理及动力学研究

Study on crystallization mechanism and kinetics of macallisterite synthesized with bischofite from salt lake

硼酸镁是一种重要的化工原料,广泛应用于玻璃、陶瓷和塑料高分子等行业中。针对活性MgO合成三方硼镁石成本高等缺点,以盐湖水氯镁石为镁源、五硼酸钠(或硼酸和氢氧化钠)为硼源,开展了水热法快速合成三方硼镁石的实验研究。采用动力学方法和拉曼光谱技术对其结晶机理及动力学进行了探讨。结果表明,温度、原料物质的量比对合成三方硼镁石影响较大,当温度为25℃或室温、五硼酸钠和氯化镁物质的量比为1∶8时,三方硼镁石的合成时间短、纯度高。水氯镁石的加入可促进五硼酸钠碱金属溶液中的B_(3)O_(3)(OH)_(4)^(-)缩聚反应生成B_(6)O_(7)(OH)_(6)^(2-),对应溶液则转化为碱土金属硼酸镁过饱和溶液,有利于六硼酸镁盐难溶化合物(三方硼镁石)的结晶析出,晶体生长机制为多核表面反应控制。该研究提供了一种三方硼镁石快速合成的方法,工艺简单且成本低,同时对盐湖镁资源综合利用也具有一定的指导意义。

Magnesium borates are important industrial chemicals which are widely used in glass,ceramics and plastic polymers,etc.Being aimed at improving the production cost of macallisterite from magnesium oxide,the synthesis of the macallisterite by hydrothermal method was investigated by using the salt lake bischofite as the magnesium source,and the sodium pentaborate(or boric acid and sodium hydroxide)as the boron source.The crystallization mechanism and kinetics of the macallisterite were also investigated by Raman spectroscopy and kinetics method.The results showed that the crystalline solid phases were dependent with the temperature and material mole ratios.The optimum temperature condition was 25℃or room temperature and the corresponding mole ratio of sodium pentaborate and bischofite was 1∶8,in which could precipitate a high purity crystalline solid phase with shorter time.The Raman results indicated that the addition of bischofite facilitated the polymerization of the B_(3)O_(3)(OH)_(4)^(-) anion into the B_(6)O_(7)(OH)_(6)^(2-) anion and the alkali metal sodium pentaborate solution transferred into the supersaturation of alkaline⁃earth metal magnesium borate,which was favorable for the crystallization of insoluble magnesium hexaborate(macallisterite).The crystal growth mechanism was controlled by the multi⁃nucleus surface reaction.This study could give a rapid synthetic method for macallisterite with simple process and low cost and also provide useful information for the comprehensive utilization of magnesium resources.