三水碳酸镁在氢氧化镁-二氧化碳-水体系中的沉淀结晶

Crystallization of MgCO_3·3H_2O in Mg(OH)_2-CO_2-H_2O system

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150~200μm;当温度升高至30~40℃时,所得晶体为30~60μm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50~55μm、直径为15μm。

The MgCl_2·6 H_2O and NH3·H_2O solution were transformed into Mg（OH）_2,then the formed highly reactive Mg（OH）_2 was reacted with CO2,transforming Mg（OH）_2 into MgCO_3·3 H_2O crystals.The effect of temperature（20~40 ℃） and the initial concentration of MgCl_2 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 MgCl_2 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 MgCO_3·3 H_2O,with a diameter of 30 ~60 μm.At 20 ℃,when the concentration of MgCl_2 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 MgCO_3·3 H_2O.When the temperature was 40 ℃,the initial concentration of MgCl_2 was 0.1 ~1.0 mol/L,all of the products were MgCO_3·3 H_2O crystals.With the increasing of the initial concentration of MgCl_2 solutions,the size of the obtained particles was decreased,and the morphology was more anomalous.In conclusion,the optimum condition of the MgCO_3·3 H_2O crystal was 40 ℃,and the initial concentration of the MgCl_2 was0.5 mol/L,the obtained MgCO_3·3 H_2O crystals with a length of 50~55 μm and a diameter of 15 μm.