The Kinetics and Surface Chemistry of Mineral Corrosion

我们将继续研究在腐蚀过程中矿物表面与水溶液相互作用的机制。特别是，我们将确定由快速酸碱反应引起的矿物溶解活化能（exp）的焓贡献，该反应发生在溶解的速率控制步骤之前。这些酸碱反应对整个反应具有明显的ph依赖性。在EAR-910583资助的研究中，我们发现酸碱反应产生的焓是exp的最大贡献（Casey and Sposito, 1992）。这种贡献随pH值和温度变化很大，并且对硅酸盐矿物的限制很差。这项研究很重要，因为反应能量学的原子模型，如分子轨道计算（如Casey等人，1990年），使用exp值作为模型精度的衡量标准。我们还将间接探索控制含有第一排过渡金属的简单矿物溶解的基本阶跃反应。我们预测，某些速率增强配体对这些矿物溶解速率的影响将系统地不同，并可与氧键的电子结构预测。这一预测是由相应溶解金属配合物周围溶剂交换反应的活化熵和活化体积的差异引起的。在以前的工作中（例如，Casey, 1991； Casey和Westrich， 1992），我们发现溶剂交换反应的反应性趋势与从溶解的氧化物或正硅酸盐矿物表面去除金属之间存在密切的对应关系。

We will continue our research into the mechanisms by which mineral surfaces interact with an aqueous solution during corrosion. In particular, we will determine the enthalpy contribution to the activation energy (Eexp) for mineral dissolution that arises from the rapid acid-base reactions which precede the rate-controlling step in dissolution. These acid-base reactions impart a distinct pH-dependence of the overall reaction. In research funded under EAR-910583, we showed that the enthalpy arising from acid-base reactions is the largest contribution to the Eexp (Casey and Sposito, 1992). This contribution varies considerably with pH and temperature, and is poorly constrained for silicate minerals. This research is important because atomistic models of the reaction energetics , such as molecular-orbital calculations (e.g., Casey et al., 1990), employ Eexp values as a gauge of the model accuracy. We also will indirectly probe the elementary step reaction controlling dissolution of simple minerals containing first-row transition metals. We predict that the affect of certain rate- enhancing ligands on the dissolution rates of these minerals will differ systematically and predictable with the delectronic structure of bonds to oxygen. This prediction arises from differences in the activation entropies and activation volumes of solvent exchange reactions around corresponding dissolved metal complexes. In previous work (e.g., Casey, 1991; Casey and Westrich, 1992) we found a close correspondence between reactivity trends for solvent-exchange reactions and metal removal from a dissolving oxide or orthosilicate mineral surface.