Abstract In the context of element migration in clay-rich media, self-diffusion coefficients of interlayer cations in swelling clay minerals obtained from molecular simulations are rarely used by macroscopic models predicting cation-exchange processes. Based on experiments and simulations, this study aims at (i) making a connection between molecular and sample scale processes to predict the dynamics of cation-exchange reactions between the interlayer space of millimetre disks of vermiculite and aqueous reservoirs, and (ii) assessing the role played by both self-diffusion and selectivity coefficients on this process. Time-resolved cation exchange experiments were performed using Ca-saturated vermiculite disks immersed in aqueous reservoirs with different NaCl or SrCl2 salinities. The results were reproduced via a finite-volume model constrained by (i) cation self-diffusion coefficients calculated by molecular dynamics simulations and (ii) interlayer selectivity coefficients drawn from “batch” cation-exchange isotherms. Results showed that considering the averaged values for both the cation-exchange selectivity coefficients and self-diffusion coefficients of the slowest interlayer cation led to good agreement between the experiments and simulations, validating the modelling strategy for the connection between the molecular and laboratory time scales. A sensitivity test regarding the influence of the two input parameters on the overall results was then performed. This study underlined a constrained upscaling strategy to better assess the role played by different intrinsic parameters of the clay/water systems (molecular self-diffusion coefficients in the interlayer space vs. selectivity coefficient) on the diffusion of cations during cation-exchange reaction in clay-rich media.

中文翻译：

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结合分子模拟和实验室实验研究膨胀粘土矿物夹层中时间分辨阳离子交换过程

摘要 在富粘土介质中元素迁移的背景下，从分子模拟获得的膨胀粘土矿物层间阳离子的自扩散系数很少用于预测阳离子交换过程的宏观模型。基于实验和模拟，本研究旨在 (i) 在分子和样品尺度过程之间建立联系，以预测蛭石毫米圆盘与含水储层之间的阳离子交换反应的动力学，以及 (ii) 评估自扩散系数和选择性系数在该过程中所起的作用。使用浸入具有不同 NaCl 或 SrCl2 盐度的水库中的 Ca 饱和蛭石盘进行时间分辨阳离子交换实验。结果是通过有限体积模型再现的，该模型受 (i) 通过分子动力学模拟计算的阳离子自扩散系数和 (ii) 从“批次”阳离子交换等温线得出的层间选择性系数的约束。结果表明，考虑到最慢层间阳离子的阳离子交换选择性系数和自扩散系数的平均值，实验和模拟之间具有良好的一致性，验证了分子和实验室时间尺度之间联系的建模策略。然后执行关于两个输入参数对整体结果的影响的敏感性测试。