Modified calcium bentonite (Ca-bentonite) is extensively used in engineered barrier systems (EBSs) for municipal and industrial disposal sites due to its high swelling potential and low hydraulic conductivity. However, few studies have focused on the micromechanism of hydration and swelling under the effect of inorganic chemical solution. In this study, free swell index (FSI) and the type and content of modified Ca-bentonite bound water under the inorganic chemical solution were quantitatively studied by using the free swell test and nuclear magnetic resonance (NMR). According to the results, modification of sodium and polymer significantly increases the FSI of Ca-bentonite, bringing it close to that of natural sodium bentonite. In addition, the chemical stability of polymer-modified bentonite is significantly higher than that of sodium-modified bentonite but less than that of natural Na-bentonite. The FSI of modified Ca-bentonite decreases with the increase of cation valence and ionic strength. distribution curves of the two types of modified bentonite are three-peak curves. With the increase of ionic strength, the content of total water and permeated hydrated water (accounting for 69%–95%) in bentonite decreases gradually, whereas the surface hydration water (accounting for 2%–31%) and free water content (accounting for 0–15%) increase. A uniform linear relationship exists between the FSI and corresponding total peak area of NMR (independent of ion valence, concentration, and bentonite type). Furthermore, a linear relationship exists between the FSI of the same type of bentonite and the relaxation time. Research results can provide data and theoretical basis for quantitative analysis and mechanism of the hydration swelling of bentonite.

中文翻译：

---

钠基和聚合物改性钙基膨润土的水化溶胀和结合水型研究

改性钙膨润土（Ca-膨润土）由于其高膨胀潜力和低导水率而广泛用于市政和工业处置场所的工程屏障系统（EBS）。然而，很少有研究关注无机化学溶液作用下水化和溶胀的微观机制。本研究利用自由溶胀试验和核磁共振（NMR）对无机化学溶液下的自由溶胀指数（FSI）和改性钙膨润土结合水的种类和含量进行了定量研究。结果表明，钠和聚合物的改性显着提高了钙基膨润土的FSI，使其接近天然钠基膨润土的FSI。此外，聚合物改性膨润土的化学稳定性明显高于钠改性膨润土，但低于天然钠膨润土。改性Ca-膨润土的FSI随着阳离子价态和离子强度的增加而降低。两种改性膨润土的分布曲线均为三峰曲线。随着离子强度的增加，膨润土中总水和渗透水化水（占 69%~95%）的含量逐渐减少，而表面水化水（占 2%~31%）和游离水含量（占0–15%) 增加。FSI 和相应的 NMR 总峰面积之间存在一致的线性关系（与离子价、浓度和膨润土类型无关）。此外，同种膨润土的FSI与弛豫时间呈线性关系。研究结果可为膨润土水化溶胀的定量分析及机理提供数据和理论依据。