Abstract Surface reactivity is a major parameter controlling mineral reactivity, and microscopic techniques investigating surface retreat with time have pointed at the heterogeneous and/or anisotropic reactivity of minerals, in relation with the diversity and stochastic distribution of energetic sites. However, in view of the discrepancies between rates determined in the laboratory, a thorough 3D approach of crystal reactivity might be particularly attractive to evaluate the respective contributions of single faces and crystal edges to the dissolution flux, and to fill the gap between the rates derived from face-specific, topography observations at micro-scale (i.e., with no contribution of the edges to dissolution) and those determined on crystal powders in continuously stirred reactors (with an overcontribution of the edges and surface defects to dissolution). Here, we provide a detailed 3D characterization of the geometry evolution and dissolution rate of a single crystal of calcite at pH 4.5 and 4.0 using X-ray micro-tomography (XMT) with a pixel size of 0.325 µm. Evaluation of the retreat and mapping of the reaction rates at the 3D crystal surface reveal a large range of dissolution rates reflecting the specific contributions of the different regions of the crystal. During dissolution and against all expectation, etch pits forming at the crystal surface progressively annihilate, primarily by intersecting with trains of steps coming from the near edge regions. The global rate determined at the crystal scale integrates the contribution of the local rates of all the crystal features, with r ¯ corner ′ > r ¯ edge ′ > r ¯ cleavage ′ > r ¯ macrostep ′ ∼ r ¯ pit ′ > r ¯ macrostep b a s e ′ . Crystal rounding reveals that contribution from the crystal edges progressively dominates the dissolution process over pit formation at the { 10 1 ¯ 4 } surfaces. The contribution of the edges to dissolution increases the crystal dissolution rate by at least 1.6 to what would be a face-specific dissolution, and will be size- and time-dependent, as suggested by a simple geometric model based on uniform or non-uniform dissolution of the faces of a model crystal. Finally, comparison of the method to vertical scanning interferometry measurements and scanning electron microscopy observations on surface portions shows that XMT imaging is robust, suggesting that its application to the dissolution/precipitation of other minerals would be highly beneficial to determine reliable rates that can be further used to model mineral reactivity.

中文翻译：

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在 3D 中检查晶体溶出度：一种在实验室中调和溶出度的方法？

摘要 表面反应性是控制矿物反应性的主要参数，研究表面随时间后退的微观技术指出矿物的异质和/或各向异性反应性与含能位点的多样性和随机分布有关。然而，鉴于实验室确定的速率之间的差异，晶体反应性的全面 3D 方法可能特别有吸引力，以评估单面和晶体边缘对溶解通量的各自贡献，并填补得出的速率之间的差距从微观尺度的面部特定地形观察（即，边缘对溶解没有贡献）和那些在连续搅拌反应器中的晶体粉末上测定的（边缘和表面缺陷对溶解的过度贡献）。在这里，我们使用像素尺寸为 0.325 µm 的 X 射线显微断层扫描 (XMT) 提供了在 pH 4.5 和 4.0 条件下方解石单晶的几何演变和溶解速率的详细 3D 表征。对 3D 晶体表面反应速率的评估和映射揭示了大范围的溶解速率，反映了晶体不同区域的特定贡献。在溶解过程中，出乎意料的是，在晶体表面形成的蚀刻坑逐渐消失，主要是通过与来自近边缘区域的一系列台阶相交。在晶体尺度上确定的全局速率整合了所有晶体特征的局部速率的贡献，具有 r¯ 角 ' > r ¯ 边缘 ' > r¯ 解理 ' > r ¯ 宏步 ' ∼ r ¯ 坑 ' > r ¯ 宏步根据 ' 。晶体圆角显示，在 {10 1 ¯ 4 } 表面，晶体边缘的贡献逐渐主导溶解过程而不是凹坑形成。正如基于均匀或非均匀的简单几何模型所表明的那样，边缘对溶解的贡献使晶体溶解速率增加了至少 1.6 倍于面特定溶解，并且与尺寸和时间有关模型晶体表面的溶解。最后，