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

埃格尔斯顿9527031矿物的溶解和生长是岩石与水和生物圈(即地球表面的环境)之间化学交流的基本形式。这项建议描述了一项研究，它使用速率松弛动力学和非稳态实验作为一种强大的新探针，来研究氧化物矿物在溶解和生长过程中运行的表面化学过程。地球表面的条件是多变的。在这种环境下，化工过程经常受到条件的瞬变和周期性扰动和波动；很少实现稳态。相比之下，我们对矿物溶解和生长动力学的理解很大程度上局限于稳态。我们对速率松弛时间(即从一个稳态转换到另一个稳态所需的时间)知之甚少，尽管有强有力的证据表明它们的存在。这对我们模拟自然界中的反应速率的能力造成了根本的限制。这项研究将测试和约束非稳态(NSS)溶解和生长动力学理论，以解决这一限制。将NSS数据系统化的理论框架结合了表面络合模型(SCM)、吸附动力学和Burton-Cabrera-Frank(BCF)理论。这种方法直接关系到其他几个长期存在的问题：1)总热力学推动力和速率之间的关系(S)；2)矿物表面的结构-反应性关联；以及3)速率影响吸附物种的作用。重要的是，它还创造了一种使用来自原位扫描探针显微镜的运动学(步长和扭结运动和相互作用)的新数据来约束理论的方法。因此，NSS动力学为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提供了一个独特的机会。使用简单的(单组分)Al、Fe和Si氧化物矿物(加上一些结构类似物)和后来使用钠长石测试的特定假设是：存在速率松弛时间；即，对突然变化(例如，pH)的响应，溶解或生长速度预计将相对于变化的突然程度缓慢地接近新的稳定状态。这将使用专门设计的流动反应堆进行湿化学测试。将记录系统对方波和正弦波变化的响应，例如，pH。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。速率松弛时间预计与相应水溶液离子的H2O置换速率相关(溶解和吸附速率也是如此)。速率松弛是由于吸附的“营养”物种的浓度和/或结构的变化(例如，Al在Al203上的浓度和/或结构的变化)。这种吸附的平衡和动力学数据将使用：a)同位素稀释，b)FTIR光谱的新用途，c)新的高分辨率静电原子力显微镜(AFM)技术，以及d)AFM得出的阶跃运动学数据与上面讨论的BCF-SCM理论预测的比较。使用了同结构(刚玉和针铁矿结构的氧化物)，以便可以利用线性自由能关系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.