Frontiers Science Center for Rare Isotopes, Lanzhou University, Lanzhou, 730000, China; Radiochemistry Lab, School of Nuclear Science and Technology, Lanzhou University, Lanzhou, 730000, China.
Subatech, UMR6457, IN2P3/CNRS/IMT Atlantique/Université de Nantes, 4 Rue Alfred Kastler, F-44307, Nantes, France.
Chemosphere. 2022 Apr;292:133402. doi: 10.1016/j.chemosphere.2021.133402. Epub 2021 Dec 22.
For the geological repository of high-level radioactive waste (HLW) built in granitic host rock，the control of buffer material (compacted bentonite) erosion and subsequent loss caused by groundwater in granite fissures is an unresolved problem of major concern. We propose here new insight into enhancing the erosion resistance of compacted bentonite by means of its electrostatic interaction with oppositely-charged layered double hydroxide (LDH). The interaction between bentonite and LDH was studied by dropwise addition of colloidal LDH into colloidal bentonite suspension, during which the variation in electrical conductivity, zeta potential and particle size proved a strong interaction between these two materials. Interestingly, in addition to their aggregation, intercalated structures of LDH and montmorillonite were found in the composite (BEN@LDH) by a combined characterization of X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM), and were confirmed by density functional theory (DFT) calculation. Colloid generation of compacted BEN@LDH under ultrasonic conditions is negligible comparing with that of compacted bentonite, indicating a significantly higher erosion resistance. Besides, a small amount of LDH by mechanically mixing with bentonite (mass ratio 1:99) can also effectively improve the erosion resistance of compacted bentonite. Moreover, BEN@LDH displayed stronger retention performance towards U(VI) and Se(IV) than bentonite under near-neutral/weakly alkaline conditions. Our results indicate that LDH is a promising additive in compacted bentonite, and this approach may be extended to common geotechnical structures built with clays and soils.
对于建在花岗岩基岩中的高放废物（HLW）地质处置库，控制缓冲材料（压实膨润土）在花岗岩裂隙水中的侵蚀和随后的损失是一个尚未解决的主要问题。我们在这里提出了一种新的见解，通过压实膨润土与带相反电荷的层状双氢氧化物（LDH）的静电相互作用来提高其抗侵蚀性。通过将胶体 LDH 逐滴加入胶体膨润土悬浮液中来研究膨润土和 LDH 之间的相互作用，在此过程中，电导率、ζ电位和粒径的变化证明了这两种材料之间的强烈相互作用。有趣的是，除了聚集之外，在复合材料（BEN@LDH）中还发现了 LDH 和蒙脱石的插层结构，这是通过 X 射线衍射（XRD）和高分辨率透射电子显微镜（HR-TEM）的综合表征发现的，并通过密度泛函理论（DFT）计算得到证实。与压实膨润土相比，压实 BEN@LDH 在超声条件下产生胶体的量可以忽略不计，这表明其抗侵蚀性显著提高。此外，少量的 LDH 通过与膨润土机械混合（质量比为 1:99）也可以有效地提高压实膨润土的抗侵蚀性。此外，在近中性/弱碱性条件下，BEN@LDH 对 U（VI）和 Se（IV）的保留性能强于膨润土。我们的结果表明，LDH 是压实膨润土的一种有前途的添加剂，这种方法可能会扩展到用粘土和土壤建造的常见岩土结构。
