Hiroshi Isobe

Dehydration processes in the meta-autunite group minerals meta-autunite, metasaléeite, and metatorbernite

Abstract We investigated dehydration processes in uranyl phosphate minerals of the meta-autunite group that consist of uranyl phosphate sheets and interlayer cations, and water molecules. Meta-autunite [Ca(UO2PO4)2⋅6H2O], metasaléeite [Mg(UO2PO4)2⋅8H2O], and metatorbernite [Cu(UO2PO4)2⋅8H2O] were selected for our study. The change in basal spacing between two adjacent uranyl phosphate sheets with temperature was examined by temperature-controlled X-ray diffraction (XRD) analysis from room temperature (RT) to 300 °C to determine structurally distinct, dehydrated phases. Thermogravimetric and differential thermal analyses (TG/DTA) were also performed under conditions similar to those used for the XRD analysis to clarify the hydration states of the dehydrated phases. Retention of the structure of the uranyl phosphate sheets under a high vacuum, equivalent to 300 °C, was confirmed by transmission electron microscopy. Meta-autunite, metasaléeite, and metatorbernite decreased their basal spacings by losing water molecules. Comparison of the TG/DTA and XRD results indicates that the changes in basal spacings of the dehydrated phases with temperature are as follows: 8.32 Å (6 H2O per unit formula) at RT, 7.31 (? H2O) and 6.68 Å (? H2O) at 75 °C, 6.34 Å (2 H2O) at 120°C, and 5.81 Å (1 H2O) at 300°C for meta-autunite; 8.29 (8 H2O) and 7.73 Å (? H2O) at RT, 6.62 Å (probably, 2 H2O) at 40 °C, 6.54 Å (2 H2O) at 160 °C, and 5.52 Å (1 H2O) at 300 °C for metasaléeite; and 8.61 Å (8 H2O) at RT, 8.07 Å (4 H2O) at 100 °C, 6.58 Å (2 H2O) at 200 °C, and 5.60 Å (1 H2O) at 300 °C for metatorbernite. The dehydration processes revealed by XRD and TG/DTA under similar experimental conditions are slightly different from those obtained by previous studies. Our results clearly demonstrate the presence of previously unknown dehydrated phases of the meta-autunite group minerals with basal spacings less than 6Å that may have distinct thermodynamic properties

Association of europium(III), americium(III), and curium(III) with cellulose, chitin, and chitosan

The association of trivalent f-elements-Eu(III), Am(III), and Cm(III)--with cellulose, chitin, and chitosan was determined by batch experiments and time-resolved, laser-induced fluorescence spectroscopy (TRLFS). The properties of these biopolymers as an adsorbent were characterized based on speciation calculation of Eu(III). The adsorption study showed that an increase of the ionic strength by NaCl did not affect the adsorption kinetics of Eu(III), Am(III), and Cm(III) for all the biopolymers, but the addition of Na2CO3 significantly delayed the kinetics because of their trivalent f-element complexation with carbonate ions. It also was suggested from the speciation calculation study that all the biopolymers were degraded under alkaline conditions, leading to their masking of the adsorption of Eu(III), Am(III), and Cm(III) on the nondegraded biopolymers. The masking effect was higher for cellulose than for chitin and chitosan, indicating that of the three, cellulose was degraded most significantly in alkaline solutions. Desorption experiments suggested that some portion of the adsorbed Eu(III) penetrated deep into the matrix, being isolated in a cavity-like site. The TRLFS study showed that the coordination environment of Eu(III) is stabilized mainly by the inner spherical coordination in chitin and by the outer spherical coordination in chitosan, with less association in cellulose in comparison to chitin and chitosan. These results suggest that the association of these biopolymers with Eu(III), Am(III), and Cm(III) is governed not only by the affinity of the functional groups alone but also by other factors, such as the macromolecular steric effect. The association of degraded materials of the biopolymers also should be taken into consideration for an accurate prediction of the influence of biopolymers on the migration behavior of trivalent f-elements.

XAFS study on Ca local structure in natural glasses and tektite

The local structures of tektite and natural glasses were studied by Ca K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) in order to provide quantitative data on bonding distances and coordination numbers. The pre-edge peak intensities of tektites are 10.7-11.7%, and those of peudotachylite, Kirauea volcanic glass, impactite, pitchstone and perlite are 6.7–10.9%. The main peak shoulder intensities of tektites are 68.3–70.7%, and other natural glasses are 63.0–63.9%. XAFS analysis indicated all tektites possess 7-coordinated Ca, but natural glasses possess 6-, 7- and 8- coordinated Ca. This study indicated that different petrogenesis of natural glasses gives different local structures of calcium.

Local structures of Ca, Ti, Fe in shergottite fusion glass

Tsubasa Tobase1, Massimo Nespolo2, Akira Yoshiasa3, Hidetomo Hongu3, Hiroshi Isobe3, Maki Okube4, Hiroshi Arima4, Kazumasa Sugiyama4 1Graduated School Of Science And Technology, Kumamoto University, Kumamoto, Japan, 2Université de Lorraine, Nancy, France, 3Kumamoto University, Kumamoto, Japan, 4Institute for Material and Research, Tohoku university, Sendai, Japan E-mail: 155d9009@st.kumamoto-u.ac.jp

Local structures of Ca, Ti and Fe in meteorite fusion crusts

The local structures of meteorite fusion crusts were studied by Ca, Ti and Fe K-edge XANES and EXAFS spectroscopy. The surface of meteorites were melted and volatilized with extreme high temperature and large temperature gradient when meteorites were rushed into atmosphere. This study indicated that meteorite fusion crusts have unique local structures. The local structures of fusion crusts differ from tektites especially in intensity of the shoulder in the rising flank of the edge in Ca XANES spectra. It is consistent with chemical composition change by the volatilization of Si at fusion during atmospheric entry. The high estimated Fe3+/ (Fe2++Fe3+) ratio in meteorite fusion crusts indicates that meteorite fusion crusts are formed into atmospheric oxidation condition. The Ca-O distances in meteorite fusion crusts are 2.612.66 A and are extremely longer than in other natural glasses. The fusion crusts have unique local structure since they experienced extremely high temperature and short quenching time. The XAFS method is effective in distinction of meteorite fusion crusts and classification of natural glass.

Weathering and precipitation after meteorite impact of Ni, Cr, Fe, Ca and Mn in K-T boundary clays from Stevns Klint

Ni, Cr, Fe, Ca and Mn K-edge XANES and EXAFS spectra were measured on K-T boundary clays from Stevns Klint in Denmark. According to XANES spectra and EXAFS analyses, the local structures of Ni, Cr and Fe in K-T boundary clays is similar to Ni(OH)2, Cr2O3 and FeOOH, respectively. It is assumed that the Ni, Cr and Fe elements in impact related glasses is changing into stable hydrate and oxide by the weathering and diagenesis at the surface of the Earth. Ca in K-T boundary clays maintains the diopside-like structure. Local structure of Ca in K-T clays seems to keep information on the condition at meteorite impact. Mn has a local structure like MnCO3 with divalent state. It is assumed that the origin on low abundant of Mn in the Fe-group element in K-T clays was the consumption by life activity and the diffusion to other parts.

Local structure of Titanium in natural glasses probed by X-ray absorption fine structure

Synchrotron radiation has been used to collect titanium K-edge absorption spectra of a suite of natural glasses (tektites, impact glasses, fault rocks and volcanic glasses). XANES and XAFS analysis provided the qualitative and quantitative information of Ti oxidation state, Ti-O distance and site geometry. Tektites possess four-, five-, six-coordinated Ti, whereas fault rock-pseudotachylite, volcanic glasses and impact glass only presented five- and six-coordinated Ti. This study indicated that different petrogenesis of natural glasses has different local structures of titanium.