Abstract
Montmorillonite is widely used as backfilled/ buffer material in radioactive waste repository facilities. However, the shortcomings of poor sorption selectivity of montmorillonite need to be improved by surface modification. The self-assembly modification of Na-montmorillonite through the intercalation of hexadecyl- trimethylammonium (HDTMA), 18-crown-6 crown ether (18C6) and 222-cryptand (crypt) into the clay’s interlayer spaces was achieved in this study. Means including X-ray diffraction (XRD), Scanning electron microscopy (SEM), thermogravimetric analysis (TG), and N2-BET analysis were applied to probe the surface properties of obtained self-assembly organoclays. Moreover, their performances were examined by conducting Cs sorption experiments.The XRD results demonstrated the expanded interlayer spaces of obtained self-assembly organoclays due to successfully intercalation of HDTMA, 18C6, and crypt molecules. SEM observation showed the aggregated appearance of self-assembly organoclays with reduced particle sizes. The FTIR analyses showed the reduced amount of water adsorbed on self-assembly organoclays after modification. The TG results revealed the excellent thermal stability of obtained organoclays.Organoclays modified with 18-crown-6 or 222-cryptand possess higher sorption selectivity toward cesium cation compared to raw montmorillonite samples. Particularly, over 10 % of increase in the Cs sorbed ratio under 0.1 N NaCl background solutions was achieved by the crypt-mmt and 18C6-mmt samples. These observations demonstrated the high Cs sorption selectivity of 18C6-mmt and crypt-mmt. In contrast, organoclays pretreated with HDTMA didn’t show any significant improvement in Cs uptake under high ionic strength solutions. The latter observation implied that HDTMA modification prior to 18C6 and crypt intercalation is not the necessary step when preparing high sorption selectivity buffer/back-filled materials.