Toward a Model for Mineral Dissolution Kinetics

本研究的目的是比较一系列成分相似且结构复杂的矿物的酸碱表面化学和溶解动力学。该系列包括凤梨石（刚玉，石英），phenakite，金绿柱石（和绿柱石）。这项研究的目的是建立简单氧化物溶解模型之间的联系，这很容易研究，和岩石形成矿物含有几个潜在的溶解点。这项研究需要确定phenakite， chrysoberyl和beryl的溶解速率规律，作为pH值和温度在15-80摄氏度范围内的函数。其他矿物的数据已经存在。研究的一个重要部分是将溶解活化能与氢离子和羟基离子的吸附焓进行比较。这种比较将确定平衡吸附焓随pH值的变化在多大程度上解释溶解活化能随溶液pH值的变化。所提出的矿物具有独特的性质，适合于建立上述联系。所有的溶解都足够缓慢，溶质扩散不会影响反应速率。因此，控制ph依赖性反应速率的酸碱表面化学可以很容易地表征。最重要的是，阳离子与氧的配位化学在整个矿物系列中是一致的。这项研究涉及到对常见造岩矿物溶解动力学的基本理解，这是了解岩石风化的基础是变质作用所必需的。

The objective of this study is to compare the acid-base surface chemistry and dissolution kinetics of a series of minerals of similar composition and increasing structural complexity. This series includes bromellite (corundum, quartz), phenakite, chrysoberyl (and beryl). This study is intended to establish a link between models for dissolution of simple oxides, which are easily studied, and rock-forming minerals containing several potential sites for dissolution. The research entails determining the dissolution rate laws for phenakite, chrysoberyl and beryl as a function of pH and temperature in the range of 15-80 degrees C. Data already exist for the other minerals. An essential part of the research is comparison of the dissolution activation energies with the enthalpies of hydrogen- and hydroxyl-ion adsorption. This comparison will determine the extent that variations in equilibrium adsorption enthalpies with pH account for the reported variation in dissolution activation energies with solution pH. The proposed minerals have properties which are uniquely suited to establish the aforementioned link. All dissolve sufficiently slowly that solute diffusion does not affect the reaction rate. Thus the acid-base surface chemistry, which controls the pH-dependence of the reaction rate, can be easily characterized. Most importantly, the coordination chemistry of cations to oxygens is consistent in the entire series of minerals. This research involves fundamental understanding of the kinetics of dissolution in common rock-forming minerals necessary to get at the basics of rock weathering are metamorphism.