Strontium Attenuation in Basaltic Aquifers: Experimental Determination of Ca2+-Na+-Sr2+-K+ Exchange Between Heulandite and Aqueous Solutions

BirdEAR-0001113拟议的研究是一项沸石-溶液相互作用的实验、理论和地质研究，旨在量化地质系统中水溶液和板蓝石之间的离子交换反应。这项研究是基于对天然方沸石中钙离子、钠离子、锶离子和钾离子交换反应的实验评估进行的。天然方钠石是一种常见的成岩沸石，已知通过离子交换在其晶体结构中浓缩锶离子。我们的目标是提供所需的热力学数据，以模拟玄武岩含水层中板蓝石和地下水之间的反应质量转移，参考来自核废料储存库的放射性90Sr的衰减。本研究包括用二元阳离子交换实验确定交换反应的热力学性质，并用X-射线衍射和核磁共振技术研究了离子交换对胡兰石晶体结构的影响。最后，将利用冰岛地热/变质系统中测量的流体和矿物组成关系来检验实验室实验和热力学分析的可信度。这项工作将在斯坦福大学、劳伦斯·利弗莫尔国家实验室和斯坦福同步辐射实验室进行。本研究的具体目的是确定：1)离子交换反应的吉布斯能和热，2)阳离子中心和中心占有率作为组成的函数的定量描述，以及3)方柱石通道间中心二元固溶体的活度-组成模型。这一结果将有助于沸石赋存的地下水含水层中碱金属和碱土金属传质的地球化学模拟。我们的发现将有助于开发地下水-沸石相互作用的启发式和定量模型，以及在被核废料污染的玄武岩含水层中90Sr的去向，这些含水层包括华盛顿州汉福德核保护区和爱达荷州爱达荷州国家工程实验室的美国能源部地下含水层，以及内华达州尤卡山的更多硅质火山岩，那里有胡兰特。

BirdEAR-0001113The proposed study is an experimental, theoretical, and geologic investigation of zeolite-solution interaction that aims to quantify ion exchange reactions between aqueous solutions and heulandite in geologic systems. Research is based on experimental evaluation of Ca2+, Na+, Sr2+, and K+ exchange reactions in natural heulandite, a common rock-forming zeolite, known to concentrate Sr2+ in its crystal structure via ion exchange. Our goal is to provide thermodynamic data required to model reactive mass transfer between heulandite and ground-waters in basaltic aquifers, with reference to attenuation of radioactive 90Sr derived from nuclear waste respositories. This study includes binary cation exchange experiments on heulandite to determine the thermodynamic properties of the exchange reactions and crystal-chemical investigation on the effects of ion exchange on the crystal structure of heulandite employing X-ray diffraction and nuclear magnetic resonance (NMR) techniques. Finally, the credibility of the laboratory experiments and thermodynamic analyses will be tested using measured fluid and mineral compositional relations in Icelandic geothermal/metamorphic systems. The work will be conducted at Stanford University, Lawrence Livermore National Laboratory, and the Stanford Synchrotron Radiation Laboratory. The specific objectives of this study are to determine: 1) Gibbs energies and enthalpies of ion exchange reactions, 2) quantitative description of cation sites and site occupancy in heulandite as a function of composition and 3) activity-composition models for binary solid solutions in the interchannel sites in heulandite. The results will facilitate geochemical modeling of alkali- and alkaline earth-metal mass-transfer in groundwater aquifers where zeolites occur. Our findings will provide essential data to help develop heuristic and quantitative models of groundwater-zeolite interaction and the fate of 90Sr in basaltic aquifers contaminated with nuclear waste such as those below the U. S. Department of Energy sites at the Hanford Nuclear Reservation, WA, and the Idaho National Engineering Laboratories, ID, as well as in more silicic volcanic rocks at Yucca Mountain, NV, where heulandite occurs.