Mineral Dissolution and Growth: A Laboratory Study of Kinetic Responses to Variable Conditions

埃格莱斯顿9527031 矿物溶解和生长是岩石与水圈和生物圈（即，地球表面的环境）。 该建议描述了一项研究，使用速率弛豫动力学和非稳态实验作为一个强大的新的探针的表面化学过程中操作的氧化物矿物的溶解和生长。 地球表面的条件是可变的。 在这种环境中的化学过程受到频繁的瞬态和周期性扰动和条件波动的影响;很少达到稳态。 相反，我们对矿物溶解和生长动力学的理解在很大程度上限于稳态。 我们对速率弛豫时间知之甚少（即，从一个稳态过渡到另一个稳态所需的时间），尽管有强有力的证据表明它们存在。 这对我们在自然界中模拟反应速率的能力施加了根本限制。 本研究将测试和约束非稳态（NSS）溶解和生长动力学的理论，解决这个限制。 在这里开发的理论框架系统化NSS数据结合表面络合模型（SCM），吸收动力学，和伯顿-卡布雷拉-弗兰克（BCF）理论。 这种方法与其他几个长期存在的问题有直接关系：1）总热力学驱动力和速率之间的关系; 2）矿物表面的结构-反应性相关性; 3）影响吸附物种速率的作用。 重要的是，它还创建了一种方法来使用新的数据的运动学（步骤和扭结运动和相互作用）从原位扫描探针显微镜约束理论。 因此，NSS动力学提供了一个独特的机会，在实验室和现场尺度上建立微观表面过程和宏观动力学行为之间的联系。 使用简单（单组分）Al、Fe和Si氧化物矿物（加上一些结构类似物）以及随后使用钠长石测试的具体假设是：响应于突然变化（例如，在pH值），溶解或生长速率预计将接近一个新的稳定状态缓慢相对于变化的快速性。 这将使用专门设计的流通反应器进行湿化学测试。 系统对方波和正弦波变化的响应，将记录pH值。 这种来自化学工程的“频率响应”技术为反应机理中的中间步骤提供了有价值的数据。 速率弛豫时间预计与相应的水溶液离子的H2O置换率（溶解和吸附速率）。 速率弛豫是由吸附的“营养”物质（例如，Al 203）。 平衡和动力学数据，这种吸附将获得使用：a）同位素稀释，B）一种新的使用FTIR光谱，c）一种新的，高分辨率的静电原子力显微镜（AFM）技术，和d）AFM衍生的步骤运动学数据的比较，上述BCF-SCM理论的预测。 使用等结构的（β-和针铁矿结构的氧化物，使线性自由能关系可以被用来系统化动力学数据。

Eggleston 9527031 Mineral dissolution and growth are basic forms of chemical communication between rocks and the hydro-, and bio-spheres (i.e., environments at the Earth's surface). This proposal describes a study that uses rate-relaxation kinetics and non steady-state experiments as a powerful new probe of surface chemical processes operating during dissolution and growth of oxide minerals. Conditions at the Earth's surface are variable. Chemical processes in this environment are subject to frequent transient and periodic perturbations and fluctuations of conditions; steady-state is rarely achieved. Our understanding of mineral dissolution and growth kinetics, in contrast is largely limited to steady-state. We know very little about rate-relaxation times (i.e., the time needed for transition from one steady-state to another), despite strong evidence that they exist. This imposes a fundamental limit on our ability to model reaction rates in nature. This study will test and constrain a theory of non-steady-state (NSS) dissolution and growth kinetics that addresses this limitation. The theoretical framework developed here to systematize NSS data combines surface complexation models (SCMs), absorption kinetics, and Burton-Cabrera-Frank (BCF) theory. This approach has direct bearing on several other long-standing problems: 1) relationship(s) between overall thermodynamic driving force and rate; 2) structure-reactivity correlation's for mineral surfaces; and 3) the role of rate-affecting adsorbed species. Importantly, it also creates a way to use new data on kinematics (step and kink motion and interaction) from in-situ scanning probe microscopy to constrain theory. NSS kinetics thus provides a unique opportunity to establish connections between microscopic surface processes and macroscopic kinetic behavior at both laboratory and field scales. Specific hypotheses tested, using simple (single component) Al, Fe, and Si oxide minerals (plus a few structural analogs), and later usi ng albite, are: Rate-relaxation times exist; i.e., in response to an abrupt change (e.g., in pH), dissolution or growth rates are expected to approach a new steady-state slowly relative to the abruptness of the change. This will be tested wet-chemically using specially designed flow-through reactors. The system response to square-wave and sine-wave variations of , e.g., pH, will be recorded. This "frequency-response" technique from chemical engineering provides valuable data on intermediate steps in reaction mechanisms. Rate-relaxation times are expected to correlate with H2O-replacement rates for corresponding aqueous ions (as do dissolution and adsorption rates). Rate-relaxation results from changes in the concentration and/or structure of adsorbed "nutrient" species (e.g., of Al on Al203). Equilibrium and kinetic data on such adsorption will be gained using : a) isotopic dilution, b) a novel use of FTIR spectroscopy, c) a new, high-resolution electrostatic atomic force microscopy (AFM) technique, and d) comparison of AFM-derived step kinematics data to the predictions of BCF-SCM theory discussed above. Iso-structural (corundum and goethite-structure oxides are used so that linear-free energy relationships can be employed to systematize kinetic data.