Effects of Al/Si ordering on feldspar dissolution: Part I. Crystallographic control on the stoichiometry of dissolution reaction
Effects of Al/Si ordering on feldspar dissolution: Part I. Crystallographic control on the stoichiometry of dissolution reaction
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DOI：
10.1016/j.gca.2013.10.047
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发表时间：
2014-02
影响因子：
5
通讯作者：
Yi Yang;Y. Min;J. Lococo;Young-Shin Jun
中科院分区：
文献类型：
--
作者：
Yi Yang;Y. Min;J. Lococo;Young-Shin Jun
长石的不协调溶解与其化学风化过程中富硅无定形界面结构的形成和演化有关。溶解的化学计量是依赖于组成的，并且这种依赖性反映了溶解反应作为表面更新和非均相化学反应的组合的性质。我们假设在连续的表面更新过程中，长石表面上的活性位点将继承原生矿物的本体结构特征，因此，长石的溶解速率不仅取决于水化学，而且取决于其晶体学性质。我们提出了一个新的形式主义，以量化的溶解速率依赖于他们的晶体学性质的长石。Al/Si有序度和长石溶解的化学计量之间的相关性预测基于这种形式主义。水化学分析，同步辐射X射线衍射与结构细化（HR-XRD），傅里叶变换红外光谱（FTIR）的组合验证了这种相关性。我们发现，溶解的速率和溶解的程度是不一致的依赖于SiOSi和SiOAl键（化学）的频率和这些链接的晶体学特性（键长，键角，和排序）在溶解mineral. Al/Si排序的知识提供了一种手段来量化的相对丰度的Si原子具有不同的反应性。使用基于C 1 <$-的结构模型，我们表明，富Al（T1）型四面体位置中的Al分布对溶解化学计量只有很小的影响，而Al在T1型和富Si（T2）型位置之间的分布主要影响溶解不一致性。更大程度的无序导致更高的溶解不一致性。作为一个暗示，我们的结果表明，硅酸盐溶解过程中界面结构的形成至少部分地受到硅酸盐骨架原子之间反应性差异的影响。
The incongruent dissolution of feldspar is associated with the formation and evolution of Si-rich amorphous interfacial structures during its chemical weathering. The stoichiometry of dissolution is compositionally dependent, and this dependence reflects the nature of dissolution reaction as a combination of surface renewal and heterogeneous chemical reaction. We hypothesize that during continuous surface renewal, reactive sites on a feldspar’s surface will inherit characteristics from the bulk structure of the primary mineral. Hence, the dissolution rate of feldspar depends not only on water chemistry but also on its crystallographic properties. We propose a new formalism to quantify the dependence of the dissolution rates of feldspars on their crystallographic properties. A correlation between the degree of Al/Si ordering and the stoichiometry of feldspar dissolution is predicted based on this formalism. This correlation is verified by a combination of water chemistry analysis, synchrotron X-ray diffraction with structure refinement (HR-XRD), and Fourier transform infrared spectroscopy (FTIR). We find that the rates of dissolution and the degree to which dissolution is incongruent depend on the frequency of SiOSi and SiOAl linkages (chemistry) and the crystallographic characteristics of these linkages (bond lengths, bond angles, and ordering) in the dissolving mineral. The knowledge of Al/Si ordering provides a means to quantify the relative abundances of Si atoms with different reactivities. Using a C 1¯-based structure model, we show that the distribution of Al within the Al-rich (T1) type of tetrahedral sites has only a minor effect on dissolution stoichiometry, whereas the distribution of Al between the T1-type and the Si-rich (T2)-type of sites affects dissolution incongruence predominantly. A greater extent of disorder results in higher dissolution incongruence. As an implication, our results suggest that the formation of interfacial structures during silicate dissolution should at least be partially affected by reactivity differences among the framework atoms of a silicate.