Investigations of the heterogeneous formation of ikaite and of the ikaite transformation as important processes for the genesis of stable calcium carbonate minerals

研究伊卡石的非均相形成和伊卡石转变作为稳定碳酸钙矿物成因的重要过程

• 批准号: 432944448
• 负责人: Professor Dr. Guntram Jordan
• 金额: --
• 依托单位: Arbeitsgebiet für anorganische und biogene Geomaterialien
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/432944448?language=en
• 关键词: Investigations; heterogeneous; formation; ikaite; transformation

Ikaite (CaCO3x6H2O) is an important calcium carbonate mineral in the cold regions of Earth. Numerous occurrences of ikaite and its pseudomorphs are documenting the significant role of the mineral as a substantial part of the polar carbon cycle. Despite its widespread occurrence, conditions of formation and stability of ikaite are poorly known. Especially, knowledge of the heterogeneous nucleation and transformation of ikaite is missing. This impedes a reliable assessment of the conditions of formation and stability of this mineral in nature. Previous work showed that quartz and mica surfaces enlarge the supersaturation range of ikaite formation at T = 0 °C significantly if compared to homogeneous conditions. Presence or absence of mineral surfaces, therefore, is a fundamentally important criterion for ikaite formation. It is still unknown, however, to which extent the effects of mineral surfaces are significant for ikaite nucleation at temperatures above 0 °C. Additionally, the effects of increased temperature on transformation of ikaite into more stable anhydrous calcium carbonates in presence of mineral surfaces are unknown. Knowledge of heterogeneous nucleation and transformation of ikaite at temperatures above the freezing point of water, however, are of immense importance for a correct evaluation of the applicability of this mineral as an indicator of cold temperatures. Moreover, knowledge of heterogeneous formation and transformation of ikaite at T > 0 °C can contribute to a significantly better understanding of the various formation paths of anhydrous CaCO3 polymorphs in the cold regions of Earth. Aim of the project, therefore, is investigating the formation and transformation process of ikaite in presence of mineral surfaces at T > 0 °C. Based on the successfully conducted cryo-mixed-batch-reactor (CMBR) experiments on heterogeneous nucleation of ikaite at T = 0 °C, we will investigate the formation conditions at T > 0 °C in the presence of quartz and mica. Furthermore, knowledge of the stability and the transformation process of ikaite in the presence of these mineral surfaces will be obtained. For these purposes, the impact of the substrates on the nucleation and transformation processes will be investigated using phase analysis (XRD) and microscopy (cryo-SEM and cryo-AFM) additionally to the CMBR-experiments.

伊凯特（CaCO 3 x6 H2O）是地球寒冷地区的一种重要碳酸钙矿物。伊凯特及其假晶的大量出现证明了这种矿物作为极地碳循环的重要组成部分的重要作用。尽管其广泛存在，但对伊凯特的形成条件和稳定性知之甚少。特别是对伊凯特的异相成核和相变过程的认识还很缺乏。这妨碍了对这种矿物在自然界中的形成条件和稳定性进行可靠的评估。先前的工作表明，与均匀条件相比，石英和云母表面在T = 0 °C时显著扩大了ikaite形成的过饱和范围。因此，矿物表面的存在或不存在是伊卡岩形成的一个根本性的重要标准。然而，在0 °C以上的温度下，矿物表面的影响在多大程度上对伊卡岩成核有重要意义，这一点仍然是未知的。此外，在矿物表面存在下，温度升高对伊凯特转化为更稳定的无水碳酸钙的影响是未知的。然而，在高于水的冰点的温度下伊卡伊特的非均质成核和转化的知识，对于正确评价这种矿物作为低温指标的适用性是非常重要的。此外，在T > 0 °C时伊卡特的非均相形成和转化的知识可以有助于更好地理解地球寒冷地区无水CaCO 3多晶型物的各种形成途径。因此，该项目的目的是研究在T > 0 °C时存在矿物表面的情况下ikaite的形成和转化过程。基于低温混合间歇反应器（CMBR）在T = 0 °C下成功进行的异相成核实验，我们将研究在石英和云母存在下，T > 0 °C时的形成条件。此外，在这些矿物表面的存在下，伊卡特的稳定性和转化过程的知识将获得。为了这些目的，除了CMBR实验之外，还将使用相分析（XRD）和显微镜（cryo-SEM和cryo-AFM）研究衬底对成核和转化过程的影响。