Incorporation of Incompatible Strontium and Barium Ions into Calcite (CaCO3) through Amorphous Calcium Carbonate
Incorporation of Incompatible Strontium and Barium Ions into Calcite (CaCO3) through Amorphous Calcium Carbonate
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DOI：
10.3390/min10030270
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发表时间：
2020-03
期刊：
影响因子：
2.5
通讯作者：
Ayaka Saito;H. Kagi;Shiho Marugata;K. Komatsu;Daisuke Enomoto;K. Maruyama;J. Kawano
中科院分区：
文献类型：
--
作者：
Ayaka Saito;H. Kagi;Shiho Marugata;K. Komatsu;Daisuke Enomoto;K. Maruyama;J. Kawano
方解石是自然界中普遍存在的矿物。具有大离子半径的重碱土元素，如Sr 2+和Ba 2+与方解石高度不相容。我们以前的研究阐明，不相容的Sr 2+离子可以通过从无定形碳酸钙（ACC）结晶而在结构上并入方解石。在本研究中，我们合成了Sr/（Sr + Ca）高达30.7 ± 0.6mol%的Sr掺杂方解石和Ba/（Ba + Ca）高达68.6 ± 1.8mol%的Ba掺杂方解石。所得到的Ba掺杂量高于Ca的方解石样品可以解释为迄今为止不存在的具有方解石结构的含Ca的碳酸钡，因为碳酸钡具有文石结构。在室温下获得的Sr掺杂和Ba掺杂的方解石样品的X射线衍射（XRD）图案显示，随着Sr/（Sr + Ca）或Ba/（Ba + Ca）比率的增加，反射113逐渐减弱。当Ba/（Ba + Ca）大于26.8 ± 1.6mol%时，反射113消失。据报道，纯方解石在高于1240 K的温度下反射113消失，这归因于方解石中CO 32 −的旋转（动态）无序。我们对Ba掺杂方解石的分子动力学（MD）模拟澄清了在室温下Ba掺杂方解石中的CO 32 −离子处于静态无序状态。CO 32 −离子明显倾斜，并从纯方解石的平衡位置移位。
Calcite is a ubiquitous mineral in nature. Heavy alkaline-earth elements with large ionic radii such as Sr2+ and Ba2+ are highly incompatible to calcite. Our previous study clarified that incompatible Sr2+ ions can be structurally incorporated into calcite through crystallization from amorphous calcium carbonate (ACC). In this study, we synthesized Sr-doped calcite with Sr/(Sr + Ca) up to 30.7 ± 0.6 mol% and Ba-doped calcite with Ba/(Ba + Ca) up to 68.6 ± 1.8 mol%. The obtained Ba-doped calcite samples with Ba concentration higher than Ca can be interpreted as Ca-containing barium carbonates with the calcite structure which have not existed so far because barium carbonate takes the aragonite structure. X-ray diffraction (XRD) patterns of the Sr-doped and Ba-doped calcite samples obtained at room temperature showed that reflection 113 gradually weakened with increasing Sr/(Sr + Ca) or Ba/(Ba + Ca) ratios. The reflection 113 disappeared at Ba/(Ba + Ca) higher than 26.8 ± 1.6 mol%. Extinction of reflection 113 was reported for pure calcite at temperatures higher than 1240 K, which was attributed to the rotational (dynamic) disorder of CO32− in calcite. Our Molecular Dynamics (MD) simulation on Ba-doped calcite clarified that the CO32− ions in Ba-doped calcites are in the static disorder at room temperature. The CO32− ions are notable tilted and displaced from the equilibrium position of pure calcite.