12:30 PM - 2:00 PM
[R2-P-05] Single-crystal X-ray diffraction study of a largely Cs-exchanged natural Ca-chabazite: crystal-chemical factors for its excellent Cs-exchange ability
Keywords:Ca-chabazite, Single-crystal X-ray Diffraction, Cs-exchange ability
The amount of contaminated water generated by the Fukushima Daiichi Nuclear Power Plant accident, caused by the Great East Japan Earthquake (March 11, 2011), continues to increase and has become a serious problem. Among the radioactive elements contained in contaminated water, 137Cs (30.1 years) and 90Sr (28.8years) with a long half-life were released in large quantities by the nuclear accident. The search and development of ion-exchangers for highly efficient recovery and removal of these radioactive elements are eagerly desired. Currently, natural zeolite minerals such as chabazite, mordenite and clinoptilolite are practically utilized at the crippled nuclear power plant as the radioactive element removers. To design and develop highly-effective radioactive element removers, it is significant to reveal the relationship between the crystal structural features and the exchange abilities for radioactive ions. Here we conduct the single-crystal X-ray diffraction study of a hydrated natural Ca-chabazite from Burnt Cabin Creek, Spray, Wheeler Co., Oregon, USA and its largely Cs-exchanged form. The sample compositions are (Ca1.86Na0.13K0.09)(Al3.98Si8.03)O24·12.38H2O for the former and (Cs2.66Ca0.45Na0.04K0.10)(Al4.04Si8.04)O24·8.52H2O for the latter.
We revealed that the Cs-exchanged form has the essentially ten occupied-sites in extraframework: four water sites (OW2’, OW3, OW4, OW5), essentially two Cs sites (Cs1/Cs1’, Cs2) and four Ca sites (Ca1, Ca2, Ca3, Ca4). The Cs+ ions more preferentially occupy the Cs1/Cs1’ site, located at/around the centers of the 8-membered ring windows, than the Cs2 site. In terms of interatomic distances, the coordination environments of the extraframework species in the chabazite crystals before and after the Cs-exchange treatment are discussed. In particular, both samples have a common feature that possible hydrogen bonds are relatively weak between water molecules and framework O atoms, whereas those are relatively strong between water molecules. On the basis of these findings, we discuss the crystal-chemical key factors for an excellent Cs-exchange ability of chabazite as a highly efficient radioactive-element remover.
We revealed that the Cs-exchanged form has the essentially ten occupied-sites in extraframework: four water sites (OW2’, OW3, OW4, OW5), essentially two Cs sites (Cs1/Cs1’, Cs2) and four Ca sites (Ca1, Ca2, Ca3, Ca4). The Cs+ ions more preferentially occupy the Cs1/Cs1’ site, located at/around the centers of the 8-membered ring windows, than the Cs2 site. In terms of interatomic distances, the coordination environments of the extraframework species in the chabazite crystals before and after the Cs-exchange treatment are discussed. In particular, both samples have a common feature that possible hydrogen bonds are relatively weak between water molecules and framework O atoms, whereas those are relatively strong between water molecules. On the basis of these findings, we discuss the crystal-chemical key factors for an excellent Cs-exchange ability of chabazite as a highly efficient radioactive-element remover.