超重力反应沉淀法制备碳酸钙的过程与形态控制

采用pH计、电导率仪、XRD原位检测了超重力反应沉淀法制备轻质碳酸钙的碳化过程及其动力学. 研究发现，碳化反应前期二氧化碳吸收为控制步骤，碳化反应后期转化为Ca(OH)2溶解控制. 同时发现在碳化过程前期有一明显的凝胶化现象，此时的pH值和电导率出现突变. XRD显示，此时有新相生成. 由于超重力环境下可以极大强化二氧化碳传质速率和微观混合，碳化时间较传统的“碳化法”缩短4倍以上. 结合过程控制，通过选择不同的工艺操作参数和相应的晶形控制剂，可以有选择性地控制碳酸钙的成核和生长，成功地合成了具有不同粒径的立方、链锁、纺锤、针状、片状、球形、花瓣、纤维等8种不同形态的碳酸钙粒子.

High-gravity Reactive Precipitation Process and Morphology Control for Precipitated Calcium Carbonate

Electrical conductivity, pH, and X-ray diffraction measurements were used to investigate the carbonation process and kinetics, of calcium carbonate synthesized using the high-gravity reactive precipitation process. Carbon dioxide adsorption was found to be the rate-controlling step during the initial stage of the carbonation process. In the later stage of the carbonation process, the rate controlling step was changed to dissolution of Ca(OH)2. In addition, gelation occurred during the initial stage of the carbonation process, and marked changes in pH and electrical conductivity were observed in this period. XRD study on the intermediate product formed during this period exhibited unique crystal structure. As a result of the augmented CO2 mass transfer rate and the intensified micro-mixing under high-gravity environment, the time required for the carbonation process has reduced by 4 times as compared to the conventional carbonation process. The precipitated calcium carbonate with different sizes and shapes (cubic, chain, needle, flake, spindle, sphere, rosette and fiber) were synthesized by means of using different operating conditions and selecting different additives to control the nucleation and the growth of the calcium carbonate.