Polymorphic change of calcium carbonate during reaction crystallization in a batch reactor
Polymorphic change of calcium carbonate during reaction crystallization in a batch reactor
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DOI：
10.1021/ie034161y
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发表时间：
2004-05-26
影响因子：
4.2
通讯作者：
Kim, WS
中科院分区：
文献类型：
--
作者：
Kim, WS;Hirasawa, I;Kim, WS
在间歇反应器体系中，采用CaCl2和Na2CO3水溶液在室温下反应结晶碳酸钙，通过调节操作条件实现了结晶碳酸钙向方解石的选择性多晶型控制。初始过饱和度和溶液pH值对无定形碳酸钙（ACC）成核的方解石和球文石的多晶型比有显着影响，从而导致产物粉末从不稳定的球文石到稳定的方解石的相变速率不同。在高过饱和度和低pH值条件下，由于ACC在结晶早期向球文石的转化，方解石相分数降低。此后，随着老化的进行，方解石的相分数增加，作为球霰石转化为方解石的结果。然而，在低过饱和度和高溶液pH的情况下，在整个反应时间内仅观察到方解石，而没有任何球霰石的重结晶。随着反应时间的延长，产物粉末中球文石的多晶型率逐渐降低，表明球文石在较低的初始过饱和度下溶解，从而消失，这与扫描电子显微镜分析得到的多晶型物的形态变化相吻合。同时，在较高的初始过饱和度下，从球文石到方解石的多晶型变化并没有产生任何形态转变。
In the reaction crystallization of calcium carbonate using a batch reactor system with aqueous CaCl2 and Na2CO3 at room temperature, the selective polymorphic control of crystalline calcium carbonate into calcite was achieved by adjusting the operating conditions. The polymorphic ratio of calcite and vaterite nucleated from amorphous calcium carbonate (ACC) was significantly influenced by the initial supersaturation and solution pH, thereby resulting in a different phase transformation rate for the product powder from unstable vaterite to stable calcite. With a high supersaturation and low solution pH, the phase fraction of calcite decreased owing to the favorable transformation of ACC into vaterite during the early stage of the crystallization. Thereafter, the phase fraction of calcite increased as a result of the transformation of vaterite into calcite as the aging progressed. However, with a low supersaturation and high solution pH, calcite was exclusively observed throughout the reaction time without any recrystallization of vaterite. The decrease in the polymorphic ratio of vaterite in the product powders with the reaction time indicated the disappearance of vaterite due to its dissolution at a low initial supersaturation, which matched well with the morphological change in the polymorphs obtained by a scanning electron microscopy analysis. Meanwhile, at a high initial supersaturation, the polymorphic changes from vaterite to calcite did not produce any morphological transformation.