Studies on Hydration Swelling and Bound Water Type of Sodium- and Polymer-Modified Calcium Bentonite

Abstract

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. T2 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 T2 relaxation time. Research results can provide data and theoretical basis for quantitative analysis and mechanism of the hydration swelling of bentonite.

Removal of amoxicillin from contaminated water using modified bentonite as a reactive material

“…Adding HTAB to the natural bentonite will enhance the efficacy of removing amoxicillin. This behavior is due to the electrostatic attraction force between the anionic molecules of the pollutants and the positive charge of the modified bentonite surface [ 31 ]. Furthermore, the spacing between the bentonite layers expanded during the modification process, resulting in the transformation of the bentonite's hydrophilic surface into a hydrophobic one.…”

Characterization of Compacted Ca- and Na-Bentonite with Copper Corrosion Products in the KAERI Underground Research Tunnel

“…Bentonite is divided into Ca-and Na-type bentonite according to the species of exchangeable cations present between the layers, and volume expansion is achieved via swelling through interlayer hydration [10][11][12][13][14]. The swelling ability of bentonite acts as a seal of the space between the disposal canister and disposal hole and blocks the inflow of groundwater from the surrounding host rock [15]. Upon closure of the repository, the surrounding bentonite is gradually saturated with the influx of natural porewater from the surrounding parent rock, while simultaneously experiencing a temperature rise owing to the radioactive decay of the waste [3,7,16].…”

“…12, x FOR PEER REVIEW 9 of 1215.2449(1) Å. Finally, the d-spacings of KJ-I and MX-80 increased by 3.6% and 19.4%, respectively.…”

Palm oil mill effluent (POME) precipitation using ammonium-intercalated clay coagulant

“…All clay-based materials based are abundant as their formation during the tecto-volcanic process spreads on Earth [13]. There are two general groups of clay minerals with specific features that are appropriate for contamination problems, those are swelling clay generally formed in the continental area, and non-swelling clay is generally formed in the oceanic area [14,15]. Based on the swelling character, clay is formed by the composition of 2:1 or the sandwich layers of octahedral alumina layer and covered by tetrahedral silica layers.…”