三水碳酸镁在氢氧化镁-二氧化碳-水体系中的沉淀结晶

摘要

The MgCl2·6H2O and NH3· H2O solution were transformed into Mg (OH)2,then the formed highly reactive Mg (OH)2 was reacted with CO2,transforming Mg (OH)2 into MgCO3· 3H2O crystals.The effect of temperature (20～40 ℃) and the initial concentration of MgCl2 solution (0.1～1.0 mol/L) on the crystal composition and morphology of the solid phase were investigated.The products were characterized by XRD,SEM,FT-IR and TG.The results showed that when the initial concentration of MgCl2 was 0.1 mol/L,the Mg (OH)2 was not reacted with CO2 at 20 ℃,the obtained crystals were amorphous Mg (OH)2,with a diameter of 150 ～ 200 μm.When the temperature was 30～40 ℃,the obtained crystals were bundle-like MgCO3·3H2O,with a diameter of 30～60 μm.At 20 ℃,when the concentration of MgCl2 increased from 0.1 mol/L to 0.5 ～1.0 mol/L,the crystal was transformed from amorphous Mg (OH)2 to bundle-like MgCO3·3H2O.When the temperature was 40 ℃,the initial concentration of MgCl2 was 0.1 ～1.0 mol/L,all of the products were MgCO3·3H2O crystals.With the increasing of the initial concentration of MgCl2 solutions,the size of the obtained particles was decreased,and the morphology was more anomalous.In conclusion,the optimum condition of the MgCO3·3H2O crystal was 40 ℃,and the initial concentration of the MgCl2 was 0.5 mol/L,the obtained MgCO3· 3H2O crystals with a length of 50～55 μm and a diameter of 15 μm.%以六水氯化镁和氨水为原料,通过合成高活性的氢氧化镁中间体来矿化二氧化碳,制备三水碳酸镁晶体.研究了反应温度(20～40℃)和氯化镁初始浓度(0.1～1.0 mol/L)对终产物组成和形貌的影响,并用X射线衍射(XRD)、扫描电镜(SEM)、红外光谱(FT-IR)、热重分析(TG)等手段对所得晶体进行表征.结果表明,当氯化镁初始浓度为0.1 mol/L时,在20℃条件下氢氧化镁与二氧化碳未发生反应,产物依然为无定型片状氢氧化镁,尺寸为150～200 μm;当温度升高至30～40℃时,所得晶体为30～60 μm的束状三水碳酸镁晶体.在20℃条件下,当氯化镁初始浓度由0.1 mol/L升高至0.5～1.0 mol/L时,所得晶体由无定型片状氢氧化镁转变为束状三水碳酸镁.当温度升高至40℃时,氯化镁初始浓度为0.1～ 1.0 mol/L时,生成的产物均为三水碳酸镁晶体,且随着氯化镁初始浓度升高晶体颗粒尺寸减小,形貌也更加不规则.实验结果得出:三水碳酸镁晶体生长最佳条件为40℃、氯化镁初始浓度为0.5 mol/L,在此条件下得到的三水碳酸镁晶体长度为50～55 μm、直径为15μm.