Most investigations into clay-mineral stability and new mineral formation within engineered barrier system (EBS) materials for geologic repositories of nuclear waste have focused on temperatures <100°C. In response to the United States Department of Energy’s interest in disposing of waste packages with higher thermal loads, higher temperature (200–300°C) and pressure (~150 bar), long-term (6-week to 6-month), hydrothermal experiments were conducted to evaluate the interaction of Opalinus Clay (wall rock) and Wyoming bentonite (clay buffer) with synthetic Opalinus Clay groundwater. Experiments were conducted in autoclaves using a flexible gold reaction cell with water:rock ratios between 6:1 and 9:1. Run products were characterized in terms of mineralogy and geochemistry. Montmorillonite remained stable at 200 and 300°C; traces of illite-smectite interstratified minerals were observed. Clay minerals in Opalinus Clay experienced significant changes at 300°C, including the formation of illite, illite-smectite, and chlorite-smectite. Montmorillonite illitization within the Wyoming bentonite EBS material was likely limited by the bulk chemistry of the system (i.e. low potassium) and newly formed illite was likely limited to the Opalinus Clay fragments, nucleating on pre-existing illite in the clay rock. Zeolite minerals with compositions between analcime and wairakite formed at 300°C along edges of Opalinus Clay fragments and within the bentonite matrix, but not at 200°C. Aqueous fluids remained undersaturated with respect to quartz in Opalinus Clay ± Wyoming bentonite 300°C experiments, and dissolution and re-precipitation of phases such as kaolinite, calcite, and smectite likely contributed to zeolite formation. These results can be applied to understanding zeolite formation, clay-mineral phase stability, and silica saturation within EBS materials of a high-temperature repository.

中文翻译：

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怀俄明州膨润土和蛋白石粘土的水热相互作用

大多数关于粘土矿物稳定性和用于核废料地质处置库的工程屏障系统 (EBS) 材料中新矿物形成的研究都集中在温度 <100°C。为了响应美国能源部对处置具有更高热负荷、更高温度 (200–300°C) 和压力 (~150 bar)、长期（6 周至 6 个月）的废物包的兴趣，进行了热液实验以评估蛋白石粘土（围岩）和怀俄明州膨润土（粘土缓冲层）与合成蛋白石粘土地下水的相互作用。实验是在高压釜中使用灵活的金反应池进行的，水与岩石的比例介于 6:1 和 9:1 之间。Run 产品在矿物学和地球化学方面进行了表征。蒙脱石在 200 和 300°C 下保持稳定；观察到伊利石-蒙脱石层间矿物的痕迹。Opalinus Clay 中的粘土矿物在 300°C 时发生了显着变化，包括伊利石、伊利石-蒙脱石和绿泥石-蒙脱石的形成。怀俄明州膨润土 EBS 材料中的蒙脱石伊利石化可能受到系统主体化学性质（即低钾）的限制，而新形成的伊利石可能仅限于 Opalinus 粘土碎片，在粘土岩中预先存在的伊利石上成核。成分介于方沸石和怀拉克特之间的沸石矿物在 300°C 下沿着 Opalinus 粘土碎片的边缘和在膨润土基质内形成，但不是在 200°C 下形成。在 Opalinus Clay ± Wyoming 膨润土 300°C 实验中，水相流体相对于石英仍然不饱和，并且相的溶解和再沉淀，例如高岭石、方解石、和蒙脱石可能有助于沸石的形成。这些结果可用于了解高温储存库 EBS 材料中的沸石形成、粘土-矿物相稳定性和二氧化硅饱和度。