The Kinetics and Surface Chemistry of Mineral Corrosion

Casey 9626553对于低温地球化学来说，没有过程比那些导致不同溶质物种之间以及矿物和相邻水相流体之间的传质过程更重要。我们建议继续进行将溶解反应组织到预测性框架中的研究。这种方法是为了证明从表面去除金属的速率系数与更好地描述溶解络合物周围的配体交换机制之间的定量相似性(Casey，1991；Casey和Westrich，1992；Ludwig等人，1995a，b)。这些过程之间的定量相似性允许建立线性自由能关系(LFER)来预测速率系数。在适当的情况下，我们可以确定矿物表面可能的速率控制的基本步骤反应，例如活化的络合物中的水运动速率，这是我们现在知道的重要因素(例如，Ludwig等人，1995a)。新的研究将扩展预测框架，以检查有机配体对金属转移速率的影响。我们检验了这样的假设，即小分子配合物的配体促进速率系数(KL)是可预测的，使用相应溶解的金属-配体配合物中溶剂的运动速度或描述溶液中金属-配体形态的平衡常数(见Ludwig等人，1995a，b)。成功的关键是获得金属-氧键强度差异很大的氧化物矿物的高质量比率数据。同样关键的是：(I)在溶解反应中选择形成单一主导表面络合物的配体，(Ii)了解吸附质子在反应中的作用，以及(Iii)表征降解产物。这项研究解决了对污染物地球化学平衡模型的普遍批评(例如，Oreskes等人，1994)，即重要的反应是缓慢的，速率系数未知。对几个配体的系统研究可能有助于结合广泛范围的化合物的Re活性，因为空间拥挤最终必须限制能够与表面金属配位的配体的大小、刚性和数量。

Casey 9626553 No processes are more essential to low-temperature geochemistry than those leading to mass transfer among distinct solute species, and between minerals and adjacent aqueous fluids. We propose to continue research that organizes dissolution reactions into a predictive framework. The approach is to demonstrate quantitative similarity between the rate coefficients for metal removal from a surface and the better-characterized mechanisms of ligand exchange around dissolved complexes (Casey, 1991; Casey and Westrich, 1992; Ludwig et al., 1995a, b). The quantitative similarity between these processes allows establishment of linear-free-energy relations (LFER) to predict rate coefficients. In suitable cases we can identify possible rate-controlling elementary step reactions at mineral surfaces, such as the rates of water movement in the activated complexes, which we now know to be important (e.g., Ludwig et al., 1995a). New research will expand the predictive framework to examine the effect of organic ligands on rates of metal transfer. We test the hypothesis that ligand-promoted rate coefficients (KL) for small-molecular-weight complexes are predictable using either the rates of solvent motion in the corresponding dissolved metal-ligand complex or the equilibrium constants that describe metal-ligand speciation in solution (see Ludwig et al., 1995a,b). Key to success is acquisition of high-quality rate data on oxide minerals that differ considerably in metal-oxygen bond strengths. Also critical are: (I) choice of ligands that form a single dominant surface complex stoichiometry in the dissolution reaction, (ii) in understanding the role of adsorbed protons in reaction, and (iii) in characterizing the degradation products. This research addresses the common criticism of equilibrium models of contaminant geochemistry (e.g., Oreskes et al., 1994) that the important reactions are slow and the rate coefficients unknown. Systematic study of a few ligands may serve to bound the re activities of a wide range of compounds because steric crowding must ultimately limit the size, rigidity, and number of ligands that can coordinate to a surface metal.