The Kinetics of Silica Dissolution: An Integrated Experimental Investigation of Quartz and Amorphous Silica Reactivity in the Mixed Solute Compositions of Natural Waters

[9903349dov]石英和无定形二氧化硅这两种最丰富的SiO2多晶物的溶解动力学对地球环境主要储层中二氧化硅的分配具有重要的控制作用。这些系统中的流体通常含有大量的主要溶质，钠、钾、钙和镁。这些阳离子大大提高了SiO2的溶解速率，而不是在纯（去离子水）中测定的。相比之下，微摩尔水平的铝在接近中性到弱酸性的ph值下表现出相反的二氧化硅溶解速率抑制作用。对速率调节效应的定量和机制理解对于预测二氧化硅迁移率的数值模型的准确性至关重要。这项研究将回答一个一级问题：溶解成分如何作为溶质混合物协同作用，以控制自然环境中复杂流体中二氧化硅溶解的净速率？采用结合地球化学动力学和表面科学技术的实验方法，本研究将量化石英和无定形二氧化硅在精心设计的溶液中的溶解速率（30-300℃），这些溶液含有溶质作为单一盐和混合物，作为浓度和ph的函数。速率将通过调整稳态二氧化硅浓度来确定，使用我们的热液混合流反应器系统在一系列反应亲和度上进行测定。将使用原位原子力显微镜、表面滴定、非原位XPS和俄歇分析对选定的二氧化硅表面进行平行研究。这些发现将使我们能够构建一个定量模型，以了解溶质如何控制溶液中结晶和无定形二氧化硅的反应性，从而开始接近现实世界的流体。

9903349DoveThe dissolution kinetics of the two most abundant SiO2 polymorphs, quartz and amorphous silica, have important controls on silica partitioning within major reservoirs of Earth environments. Fluids throughout these systems typically contain significant concentrations of the major solutes, sodium, potassium, calcium and magnesium. These cations greatly enhance SiO2 dissolution rates over those measured in pure (deionized) water. In contrast, micromolar levels of aluminum exhibit an opposing rate-inhibition of silica dissolution at near-neutral to weakly-acidic pH. A quantitative and mechanistic understanding of rate-mediating effects is essential to the accuracy of numerical models which predict silica mobility. This study will answer a first order question: How do dissolved constituents act in concert as a solute mixture to control net rates of silica dissolution in the complex fluids of natural environments? Using an experimental approach that integrates techniques from geochemical kinetics and surface science, this study will quantify rates of quartz and amorphous silica dissolution (30-300 degrees C) in carefully designed solutions that contain solutes as single salts and mixtures as a function of concentration and pH. Rates will be determined using our hydrothermal mixed flow reactor system over a range of reaction affinity by adjusting steady state silica concentrations. Parallel investigations of selected silica surfaces will be conducted using in situ Atomic Force Microscopy, surface titrations, and ex situ XPS and Auger analyses. The findings will allow us to construct a quantitative model for how solutes control the reactivity of crystalline and amorphous silica in solutions that begin to approximate real-world fluids.