Crystal structure of pollucite

Kamiya, Naoki; Nishi, Kazufumi; Yokomori, Yoshinobu

doi:10.1524/zkri.2008.1103

Cited by 19 publications

(7 citation statements)

References 14 publications

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“…Figure 1 shows the channel system in pollucite and several Cs + ions. The distance between two Cs + ions in the channel is 5.92 Å1112. The channel is constructed from 6-oxygen rings and has a diameter of 2.8 Å131415.…”

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Final storage of radioactive cesium by pollucite hydrothermal synthesis

Yokomori

Asazuki

Kamiya

et al. 2014

Sci Rep

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The Fukushima nuclear accident has highlighted the importance of finding a better final storage method for radioactive cesium species. Cs is highly soluble in water, and can easily exchange with other alkali ions in zeolites or clays to form stable complexes. However, Cs+ is released from Cs+ complexes into water when surrounded by an excess of water. Pollucite may be the best final storage option for Cs+, but its typical synthesis requires heating to about 1200°C in air. Here, we show that the hydrothermal synthesis of pollucite can be completed at 300°C in three hours from any zeolite or clay. Furthermore, our procedure does not require ion exchange before synthesis. Radioactive Cs is usually found in complexes with clays. At that time, this method only requires calcium hydroxide, water, and three hours of hydrothermal synthesis, so the process is both inexpensive and practical for large-scale application. Pollucite is an analog of analcime zeolite, and contains a channel system 2.8 Å in diameter, which is formed by 6-oxygen rings. As the diameter of Cs+ is 3.34 Å and each Cs+ exists independently within a separate portion of the channel, Cs+ cannot exit the pollucite framework without breaking it.

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Final storage of radioactive cesium by pollucite hydrothermal synthesis

Yokomori

Asazuki

Kamiya

et al. 2014

Sci Rep

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“…This leads to specific cation-ordering schemes for Cs-pollucites, partially substituted by Na + . 34 A distinction needs to be made between the as-synthesized and post-synthetically modified zeolites. Extra-framework cations in zeolites often can be readily replaced by a range of other cations, a modification greatly impacting the stability of the material.…”

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Structural Aspects Affecting Phase Selection in Inorganic Zeolite Synthesis

et al. 2022

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A guideline for zeolite phase selection in inorganic synthesis media is proposed, based on a systematic exploration of synthesis from inorganic media using liquid Na+, K+, and Cs+ aluminosilicate. Although the Si/Al ratio of the zeolites is a continuous function of the synthesis conditions, boundaries between topologies are sharp. The here-derived phase selection criterion relates the obtained zeolite topology to the Si/Al ratio imposed by the synthesis medium. For a given Si/Al ratio, the framework with the highest occupation of topologically available cation sites is favored. The large number of published zeolite syntheses supporting the observation provides strong indication that the concept is applicable in a larger context. The proposed criterion explains how minor variations in the composition of inorganic synthesis media induce the commonly occurring, abrupt changes in topology. It highlights underlying reasons causing the strict demarcation of stability fields of the as-synthesized zeolites experimentally observed in inorganic synthesis.

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“…The crystal structure of tetragonal pollucite was described in detail by Frank-Kamenetskaya et al (1995) (Table 1). Crystal-structure refinements of tetragonal and monoclinic modifications of synthetic analogues of pollucite were reported by Yanase et al (1997) and Kamiya et al (2008), respectively (Table 1).…”

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KIRCHHOFFITE, CsBSi2O6, A NEW MINERAL SPECIES FROM THE DARAI-PIOZ ALKALINE MASSIF, TAJIKISTAN: DESCRIPTION AND CRYSTAL STRUCTURE

Agakhanov¹,

Pautov²,

Karpenko³

et al. 2012

The Canadian Mineralogist

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Kirchhoffite, CsBSi 2 O 6 , is a new species of silicate mineral from the Darai-Pioz alkaline massif in the upper reaches of the Darai-Pioz River, in the area of the joint Turkestansky, Zeravshansky and Alaisky ridges, Tajikistan. It occurs as equant grains 10 to 80 mm in diameter, associated with quartz, pectolite, baratovite, polylithionite, aegirine, fluorite, leucosphenite, pyrochlore, neptunite and reedmergnerite. Kirchhoffite is colorless, transparent with a white streak, and a vitreous luster; it does not fluoresce under ultraviolet light. No cleavage or parting was observed. The Mohs hardness is 6 to 6½, and it is brittle with a conchoidal fracture. The measured and calculated densities are 3.62(2) and 3.639 g/cm 3 , respectively. Kirchhoffite is uniaxial (+) with indices of refraction v = 1.592(2),  = 1.600(2). The mineral is tetragonal, space group I4 1 /acd, a 13.019(2), c 12.900(3) Å, V 2186.3(1) Å 3 , Z = 16, a : c = 1 : 0.9909. The six strongest lines in the X-ray powder diffraction pattern are [d in Å(I)(hkl)] are 3.26(100) . Chemical analysis by electron and ion microprobes gave SiO 2 40.47, B 2 O 3 11.27, K 2 O 0.11, Cs 2 O 48.16, Rb 2 O 0.09, for a sum of 100.10 wt.%. The resulting empirical formula on the basis of six atoms of oxygen is (Cs 1.02 K 0.01 ) S1.03 B 0.96 Si 2.02 O 6 , ideally CsBSi 2 O 6 . The crystal structure of kirchhoffite was refined to an R 1 index of 3.1% based on 487 observed reflections collected on a four-circle diffractometer with MoKa X-radiation. In the structure, there are two tetrahedrally coordinated sites: Si is occupied by silicon, = 1.610 Å, B is occupied by boron, = 1.465 Å, and Cs is [12]-coordinated, = 3.301 Å. Tetrahedra form a [BSi 2 O 6 ] framework, the topology of which is identical to that of tetragonal pollucite, CsAlSi 2 O 6 . The [12]-coordinated Cs atoms occupy the channels along [111] formed by six-membered rings of tetrahedra. Kirchhoffite, CsBSi 2 O 6 , is a B analogue of the tetragonal modification of pollucite.

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Crystal structure of pollucite

Cited by 19 publications

References 14 publications

Final storage of radioactive cesium by pollucite hydrothermal synthesis

Final storage of radioactive cesium by pollucite hydrothermal synthesis

Structural Aspects Affecting Phase Selection in Inorganic Zeolite Synthesis

KIRCHHOFFITE, CsBSi2O6, A NEW MINERAL SPECIES FROM THE DARAI-PIOZ ALKALINE MASSIF, TAJIKISTAN: DESCRIPTION AND CRYSTAL STRUCTURE

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