Ion specific effects on the pressure solution of calcite single crystals
Ion specific effects on the pressure solution of calcite single crystals
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DOI：
10.1016/j.gca.2020.04.010
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发表时间：
2020-07-01
影响因子：
5
通讯作者：
Espinosa-Marzal, Rosa M.
中科院分区：
文献类型：
--
作者：
Diao, Yijue;Li, Anqi;Espinosa-Marzal, Rosa M.
碳酸盐岩的压溶作用参与了许多发生在地表或近地表的地球物理和地球化学过程，但对其基本认识还很欠缺。本文用扩展表面力装置（SFA）研究了方解石单晶在水、NaCl和CaCl2盐水中的压溶过程。这种高度机械和热稳定的测量技术能够测量两个单方解石晶体在压力下溶解的变形，以及作为载荷和流体成分的函数的高精度变形率。在水中的测量揭示了扩散和溶解限制的情况。此外，方解石的压力溶液减速与小浓度的NaCl相比，CaCO3饱和溶液，而速率促进增加到100 mM NaCl，反映了至少两种不同的机制的竞争。相比之下，加入少量的CaCl 2已经加速了方解石的压力溶解。这些实验结果不能仅仅解释通过增加溶解度的方解石与离子强度，一般建议。相反，它们与界面组合物的离子特异性效应和方解石的水合结构在小于类似于25 MPa的施加压力下的扭曲是一致的。这一工作为方解石的压溶提供了基础知识。更广泛地说，这里开发的新技术可以应用于其他脆性和不可剥离的矿物，这显着扩大了SFA的应用。(C)2020爱思唯尔有限公司保留所有权利。
Pressure solution of carbonate-based rocks participates in many geophysical and geochemical processes occurring at or near the Earth's surface, but fundamental knowledge is still lacking. Here, the pressure solution of calcite single crystals in water, NaCl and CaCl2 brines was investigated with an extended surface forces apparatus (SFA). This highly mechanically and thermally stable measuring technique enables to measure the deformation of two single calcite crystals undergoing pressure solution and the deformation rates with high precision as a function of load and fluid composition. The measurements in water reveal both diffusion- and dissolution-limited scenarios. Further, the pressure solution of calcite decelerates with a small concentration of NaCl compared to CaCO3-saturated solution, while the rate is promoted with an increase to 100 mM NaCl, reflecting the competition of at least two different mechanisms. In contrast, the addition of small concentrations of CaCl2 already speeds up calcite's pressure solution. These experimental results cannot be solely explained via the increase in solubility of calcite with ionic strength, as generally proposed. Instead, they are consistent with the ion-specific effects of the interfacial composition and the distortion of the hydration structure of calcite under an applied pressure smaller than similar to 25 MPa. This work advances the fundamental knowledge of pressure solution of calcite. More broadly, the novel technique developed here can be applied to other brittle and unexfoliable minerals, which notably expands the applications of SFA. (C) 2020 Elsevier Ltd. All rights reserved.