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<p>Bentonite barriers in high-level radioactive waste (HLW) repositories are expected to interact with alkaline fluids released from degrading cementitious materials, potentially compromising long-term safety. While previous studies have primarily relied on batch or one-dimensional flow tests, these approaches often fail to adequately represent the diffusion-dominated conditions characteristic of repository environments. In this study, an innovative two-dimensional diffusion cell method was proposed to evaluate bentonite degradation under more realistic, diffusion-controlled conditions. Long-duration (24-month) experiments were conducted on GMZ bentonite using NaOH and KOH solutions (pH 12-13.8) as analogues of early-age cement porewater, with periodic solution replacement to simulate a continuous alkaline supply. A quantitative analysis of cation exchange and adsorption processes was also performed. The results showed that at pH values below 13.8, the introduced cations (Na⁺ or K⁺) were almost entirely adsorbed. However, at pH 13.8, dissolution of montmorillonite occurred after 6 months, leading to a reduction in adsorption capacity. K⁺ ions exhibited a stronger affinity for bentonite, replacing 56.71% of the native Na⁺ ions. After accounting for ion exchange, the maximum adsorption capacities of Na⁺ and K⁺ ions, as determined by the Langmuir model, were 17.13&#xa0;mg/g and 30.74&#xa0;mg/g, respectively. Furthermore, fixation of K⁺ ions induced interlayer collapse, indicating the onset of illitization. Notably, the findings demonstrated that potassium-rich cement porewaters posed a greater risk to the sealing performance of bentonite than sodium-rich solutions.</p>

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Assessing GMZ bentonite degradation by alkaline solutions in long duration tests

  • 期刊论文

  • 发表日期：

    2026年6月25日

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  • Yanmei Tong,
  • Eng-Choon Leong,
  • Huyuan Zhang,
  • Quanquan Jia

摘要

Bentonite barriers in high-level radioactive waste (HLW) repositories are expected to interact with alkaline fluids released from degrading cementitious materials, potentially compromising long-term safety. While previous studies have primarily relied on batch or one-dimensional flow tests, these approaches often fail to adequately represent the diffusion-dominated conditions characteristic of repository environments. In this study, an innovative two-dimensional diffusion cell method was proposed to evaluate bentonite degradation under more realistic, diffusion-controlled conditions. Long-duration (24-month) experiments were conducted on GMZ bentonite using NaOH and KOH solutions (pH 12-13.8) as analogues of early-age cement porewater, with periodic solution replacement to simulate a continuous alkaline supply. A quantitative analysis of cation exchange and adsorption processes was also performed. The results showed that at pH values below 13.8, the introduced cations (Na⁺ or K⁺) were almost entirely adsorbed. However, at pH 13.8, dissolution of montmorillonite occurred after 6 months, leading to a reduction in adsorption capacity. K⁺ ions exhibited a stronger affinity for bentonite, replacing 56.71% of the native Na⁺ ions. After accounting for ion exchange, the maximum adsorption capacities of Na⁺ and K⁺ ions, as determined by the Langmuir model, were 17.13 mg/g and 30.74 mg/g, respectively. Furthermore, fixation of K⁺ ions induced interlayer collapse, indicating the onset of illitization. Notably, the findings demonstrated that potassium-rich cement porewaters posed a greater risk to the sealing performance of bentonite than sodium-rich solutions.