Immobilization of cesium into pollucite structure by hydrothermal hot-pressing.

Yanagisawa, Kazumichi; Nishioka, Mamoru; Yamasaki, Nakamichi

doi:10.3327/jnst.24.51

Cited by 27 publications

(17 citation statements)

References 14 publications

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“…This is typically accomplished by hydrothermally hot pressing a zeolite loaded with the target isotope during which a phase transition cccurs that results in an analcime phase.611 A comparison of the parent zeolite structure to that of the ANA-type product reveals that large cavities present in the former are collapsed by the hydrothermal process, essentially 'shrink wrapping" or trapping the cation in the lattice. Experimentally, the leach rate of Cs in the collapsed lattice is small and, depending on conditions of preparation, ranges from approximately 10-4 to 1o-S g/m2-d. 11 The purpose of this study is to investigate the behavior of "cations" in zeolites in general with specific application to materials that have been suggested as storage matrices for radioactive material. To this end, we have studied a series of Group IA atoms (Na, K, Rb, Cs) intercalated into the analcime framework.…”

Section: Introductionmentioning

confidence: 99%

An ab Initio Periodic Hartree-Fock Study of Group IA Cations in ANA-Type Zeolites

Anchell¹,

White²,

Thompson³

et al. 1994

J. Phys. Chem.

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This study investigates the electronic structure of Group IA cations intercalated into zeolites with the analcime (ANA) framework using ab initio periodic HartreeFock theory. The purpose of the study is to gain a better understanding of the role played by electron-donating species in zeolites in general, with specific applications to materials that have been suggested as storagematrices for radioactive materials. The effect of the intercalated species (Na, K, Rb, and Cs) on the electronic structure of the zeolite is presented on the basis of an analysis of the total and projected density of states, Mulliken charges, and charge density differences. The results of those analyses indicate that, relative to a charge neutral atomic state, the Group IA species donate an electron to the zeolite lattice and interact most strongly with the s and p atomic states of oxygen as the species are moved through the lattice. In addition, estimates of the self-diffusion constants of Na, K, Rb, and Cs based upon a one-dimensional diffusion model parameterized from the ab initio total energy data will be presented. We find that the estimated self-diffusion rate decreased markedly with increasing cation size, and that the diffusion rate of Cs was essentially zero in bulk pollucite. The cationic charge is unchanged as the species moves through the lattice. This indicates that model potentials based upon an ionic interpretation of the Group IA species may be reasonable.

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Section: Introductionmentioning

confidence: 99%

An ab Initio Periodic Hartree-Fock Study of Group IA Cations in ANA-Type Zeolites

Anchell¹,

White²,

Thompson³

et al. 1994

J. Phys. Chem.

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“…The high Cs-content of approximately 40 wt% in pollucite exceeds that of any Cs-containing glass ceramics or zeolites (Donald et al 1997). Furthermore, the Cs leaching rate indicates that this material might be used for long-term storage of 137 Cs at ambient conditions (Yanagisawa et al 1987). We deemed it important to further explore the hightemperature and high-pressure chemistry of the new polluciterelated phase obtained by the P/T-treatment of Cs-natrolite, to assess processes that might affect its use.…”

Section: Discussionmentioning

confidence: 99%

Topotactic and reconstructive changes at high pressures and temperatures from Cs-natrolite to Cs-hexacelsian

Hwang

Seoung

Gatta

et al. 2015

American Mineralogist

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Synchrotron X-ray powder diffraction experiments have been performed on dehydrated Csexchanged natrolite to systematically investigate successive transitions under high pressures and temperatures. At pressures above 0.5(1) GPa using H 2 O as a pressure-transmitting medium and after heating to 100 °C, dehydrated Cs 16 Al 16 Si 24 O 80 (deh-Cs-NAT) transforms to a hydrated phase Cs 16 Al 16 Si 24 O 80 ·16H 2 O (Cs-NAT-II), which has a ca. 13.9% larger unit-cell volume. Further compression and heating to 1.5 GPa and 145 °C results in the transformation of Cs-NAT-II to Cs 16 Al 16 Si 32 O 96 (anh-Cs-POL), a H 2 O-free pollucite-like triclinic phase with a 15.6% smaller unit-cell volume per 80 framework oxygen atoms (80O f ). At pressures and temperatures of 3.7 GPa and 180 °C, a new phase Cs 1.547 Al 1.548 Si 6.452 O 16 (Cs-HEX) with a hexacelsian framework forms, which has a ca. 1.8% smaller unit-cell volume per 80O f . This phase can be recovered after pressure release. The structure of the recovered Cs-HEX has been refined in space group P6 3 /mcm with a = 5.3731(2) Å and c = 16.6834(8) Å, and also been confirmed by HAADF-STEM real space imaging. Similar to the hexacelsian feldspar (i.e., BaAl 2 Si 2 O 8 ), Cs-HEX contains Cs + cations that act as bridges between the upper and lower layers composed of tetrahedra and are hexa-coordinated to the upper and lower 6-membered ring windows. These pressure-and temperature-induced reactions from a zeolite to a feldspar-like material are important constraints for the design of materials for Cs + immobilization in nuclear waste disposal.

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“…One study [6] described a multi-step process with cesium hydroxide, water, aluminum, powder, and SiO 2 as starting materials to prepare a sol which was hydrothermally processed at 220°C for 2-24 h to produce a dry powder. They achieved 95% theoretical density after sintering at 1500°C for 10 h. Yanagisawa et al [7] created pollucite structures for cesium by hydrothermal alteration of alumino-silicate, quartz, and Al(OH) 3 . They found that pollucite could be formed at 200°C under alkaline conditions.…”

Section: Introductionmentioning

confidence: 98%