氯化镁-氢氧化钠复合添加剂制备文石型碳酸钙

采用碳化法，使用氯化镁和氢氧化钠复合添加剂，制备含文石相的沉淀碳酸钙。采用X射线衍射（XRD）、透射电镜（TEM）对产物的晶型和形貌进行表征。讨论了氢氧化钠添加比例、氢氧化钙浓度以及碳化反应温度等工艺条件对实验结果的影响，并分析了过程的反应机理。结果表明：产物中的文石相来自于碳酸钙在氢氧化镁沉淀上的异相成核和生长，方解石相来自于碳酸钙在溶液中的均相成核和生长；氢氧化钠的加入降低了溶液中碳酸钙的过饱和度，抑制了均相成核过程，降低了氯化镁的添加比例。在碳化反应温度为30 ℃、氢氧化钙浓度为1.7~ 2.0 mol/L、氢氧化钠与氯化镁物质的量比为2.6条件下，对文石型碳酸钙的生成较为有利。

Preparation of aragonite calcium carbonate by using composite additive MgCl2-NaOH

The aragonite calcium carbonate was synthesized with composite additive MgCl2 and NaOH by gas-liquid carbo- nization method.The morphology and crystal structure of products were characterized by XRD and TEM.The effects of process conditions，such as NaOH addition ratio，Ca（OH）2 concentration，and reaction temperature，on the experimental results were discussed and the reaction mechanism of the process was also analyzed.Results showed that the aragonite in the products was formed by heterogeneous nucleation and growth on the precipitation of Mg（OH）2，and the calcite formed by homogeneous nucleation and growth of calcium carbonate in the solution; the addition of NaOH reduced the supersaturation of calcium car- bonate in the solution，inhibited the homogeneous nucleation process and reduced the adding ratio of MgCl2.The high content of aragonite calcium carbonate can be prepared at the conditions that the initial carbonization temperature of 30 ℃，the con-centration of Ca（OH）2 of 1.7~2.0 mol/L，and the amount-of-substance ratio of NaOH to MgCl2 of 2.6.