On the crystal structure and crystal chemistry of pollucite, (Cs,Na)16Al16Si32O96·nH2O: A natural microporous material of interest in nuclear technology
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G. Diego Gatta
Abstract
The crystal structure and crystal chemistry of two natural pollucite samples, from Buckfield, Oxford County, Maine (sample M3), and from Kanzit Mawaie, Laghman, Nooristan, Afghanistan (sample N5), have been investigated by means of wavelength-dispersive X-ray microanalysis, thermogravimetric analysis, single-crystal X-ray and neutron diffraction, and single-crystal Fourier-transform infrared spectroscopy. The X-ray and neutron diffraction patterns of the two pollucite crystals show a metrically cubic unit cell [with aM3 = 13.6914(6) Å and aN5 = 13.6808(6) Å by neutron diffraction data; the deviation from isometry is <1.5σ(li), where li is the unrestrained unit-cell length] and the reflection conditions are consistent with the space group Ia3d. Anisotropic neutron structural refinements gave final agreement indices: R1 = 0.0543 for 32 refined parameters and 372 unique reflections with Fo > 4σ(Fo) for M3 and R1 = 0.0693 for 31 refined parameters and 331 unique reflections with Fo > 4σ(Fo) for N5. The structure refinements show a disordered Si/Al-distribution in the tetrahedral framework. The analysis of the difference-Fourier maps of the nuclear density confirms the presence of extraframework water molecules with oxygen sharing the Cs site (at 1/8, 1/8, 1/8, Wyckoff-16b position). However, the minima, ascribable to the proton sites, are very weak in density. Two possible proton positions, leading to a reasonable H2O configuration, are given, and the possible hydrogen bonding is described. Sodium is located at 1/4, 1/8, 0 (Wyckoff-24c position). The main IR absorption bands in the regions typical of H2O are assigned, and the presence of hydroxyls in the studied samples is ruled out. Neutron diffraction and FTIR data agree with the presence of very weak hydrogen bonds in the structure. The detailed description of the crystal structure and crystal chemistry of pollucite (e.g., Si/Al-distribution, configuration of the extra-framework content, possible hydrogen bonding scheme) reported in this study is the key to understand the high thermo-elastic stability of pollucite, the immobility of Cs at non-ambient conditions, and the extremely low leaching rate of Cs, which make this open-framework silicate a promising material with potential use for fixation and deposition of Cs radioisotopes
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- Review Paper. Microbe-clay mineral interactions
- Chemical substitutions, paragenetic relations, and physical conditions of formation of högbomite in the Sittampundi layered anorthosite complex, South India
- Miguelromeroite, the Mn analogue of sainfeldite, and redefinition of villyaellenite as an ordered intermediate in the sainfeldite-miguelromeroite series
- Mechanism and kinetics of a mineral transformation under hydrothermal conditions: Calaverite to metallic gold
- A statistical reassessment of the evidence for the racemic distribution of quartz enantiomorphs
- On the crystal structure and crystal chemistry of pollucite, (Cs,Na)16Al16Si32O96·nH2O: A natural microporous material of interest in nuclear technology
- The effect of fluid inclusion size on determination of homogenization temperature and density of liquid-rich aqueous inclusions
- Effect of SiO2, total FeO, Fe3+/Fe2+, and alkali elements in basaltic glasses on mid-infrared
- Influence of cation size on the low-temperature heat capacity of alkaline earth metasilicate glasses
- The high-pressure–high-temperature behavior of bassanite
- Geochemistry of reversible hydratable tephra from the Trans Mexican Volcanic Belt
- Physical contradictions and remedies using simple polythermal equations of state
- Thermodynamic and crystallographic properties of kornelite [Fe2(SO4)3·~7.75H2O] and paracoquimbite [Fe2(SO4)3·9H2O]
- Humidity-induced phase transitions of ferric sulfate minerals studied by in situ and ex situ X-ray diffraction
- In situ Raman spectroscopy of MgSiO3 enstatite up to 1550 K
- Optical spectroscopic study of tetrahedrally coordinated Co2+ in natural spinel and staurolite at different temperatures and pressures
- New insights into smectite illitization: A zoned K-bentonite revisited
- The hydrothermal conversion of kaolinite to kalsilite: Influence of time, temperature, and pH
- Sideronatrite, Na2Fe(SO4)2(OH)·3H2O: Crystal structure of the orthorhombic polytype and OD character analysis
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- Mechanism of wollastonite carbonation deduced from micro- to nanometer length scale observations
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- Letter. Magnetite-free, yellow lizardite serpentinization of olivine websterite, Canyon Mountain complex, N.E. Oregon
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