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

9903349确实，石英和无定形二氧化硅这两种最丰富的二氧化硅晶型的溶解动力学对地球环境主要储集层中的二氧化硅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二氧化硅的溶解速率，超过了在纯净(去离子)水中测量的溶解速率。相反，微摩尔水平的铝表现出相反的速率-在近中性到弱酸性的pH条件下抑制二氧化硅的溶解。对速率中介效应的定量和机理的理解对于预测二氧化硅迁移率的数值模型的准确性是至关重要的。这项研究将回答第一个问题：在自然环境的复杂流体中，溶解成分如何作为溶质混合物协同作用，控制二氧化硅的净溶解速率？这项研究采用了一种综合了地球化学动力学和表面科学技术的实验方法，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摄氏度)，这些溶液包含作为单一盐和混合物的溶质，作为浓度和pH的函数。速率将使用我们的水热混合流动反应器系统，通过调整稳态二氧化硅浓度在反应亲和力范围内确定。将使用原位原子力显微镜、表面滴定以及非原位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，说明溶质如何控制结晶和无定形二氧化硅在开始接近真实世界流体的溶液中的反应性。

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.