盐湖卤水制备棒状氢氧化镁

Preparation of rod-like magnesium hydroxide from brine

以卤水浓缩结晶得到的水氯镁石为原料,采用两步法制备棒状氢氧化镁,即先用氨法制备纤维状碱式氯化镁(Mg3Cl(OH)5·4H2O)前驱体,再将前驱体用烧碱转化为棒状氢氧化镁。探讨Mg2+浓度、反应时间、陈化时间对前驱体成分和形貌的影响。在碱式氯化镁转化为氢氧化镁的过程中,探讨反应溶剂的组成与反应温度对氢氧化镁形貌的影响。研究结果表明:只有Mg2+浓度大于3.0 mol/L时才能得到碱式氯化镁,Mg2+浓度小于3.0 mol/L时只能得到氢氧化镁;随着反应时间的增加,前驱体部分转化为氢氧化镁;随着陈化时间的延长,前驱体结晶趋于完善,粒子表面更加光滑规则,长径比由8.3增加到35.6;溶剂组成对氢氧化镁的形貌影响显著,在纯水体系中,氢氧化镁团聚严重,棒状颗粒少,在乙醇体系中,氢氧化镁分散性好,表面光滑,棒状粒子产率高。在乙醇体系中,40℃反应1 h,得到长径比大于25.0,纯度达99.8%以上的棒状氢氧化镁。

Two-step method was adopted to prepare rod-like magnesium hydroxide using bischofite as raw material. The preparation process consists of the synthesis of a precursor called fibrous basic magnesium chloride （Mg3Cl（OH）5·4H2O） and the conversion of the resulting precursor to magnesium hydroxide. The effects of concentration of Mg2＋, reaction temperature and aging time on the composition and shape of precursor were investigated. In the process of precursor conversion, the effects of solvent composition and reaction time on magnesium hydroxide were discussed. The results show that the basic magnesium chloride is prepared when the concentration of Mg2＋ is more than 3.0 mol/L, otherwise only magnesium hydroxide is obtained. With the increase of the reaction time, basic magnesium chloride converts into magnesium hydroxide, but prolonging aging time is favorable to obtain smooth particles with aspect ratio increasing from 8.3 to 35.6. The solvent composition has a great influence on the morphology of magnesium hydroxide. The rod-like magnesium hydroxide is obtained by heating the alcohol-containing solution at 40℃ for I h. Its aspect ratio can reach more than 25.0 and purity can reach 99.8%.