We have measured high-precision W isotope ratios for series of carbonaceous and ordinary chondrites. The resulting ¹⁸⁴W/¹⁸³W ratios for three carbonaceous chondrites (Murchison CM2, Y-793321 CM2, and Y-86751 CV3) did not vary significantly from that of the W isotopic standard (NIST SRM 3163) and various terrestrial rocks, whereas the ¹⁸⁴W/¹⁸³W ratios for Allende CV3 showed ∼0.4ε lower value than the other chondrites and terrestrial samples. This deficiency in the measured ¹⁸⁴W/¹⁸³W ratio for the Allende CV3 could not be attributed to the incomplete digestion of acid-resistive presolar components such as SiC grains with abundant s-process nuclides, because the SiC contents in the Allende was significantly lower than those for other carbonaceous chondrites. Several possible explanations for the deficiency in the ¹⁸⁴W found in the Allende CV3 were explored. We conclude the results could be best explained by the isotopic heterogeneity of W by contribution of r-process enriched components to the source material of the Allende CAIs. The finding is consistent with the recent observation of some CAIs in Allende was enriched in the r-process nuclide of W (Burkhardt et al., 2008) and supported by the fact that the CAI contents in the Allende chondrite are significantly higher than that in other carbonaceous chondrites.

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The partitioning of Y and Ho between CaCO₃ (calcite and aragonite respectively) and seawater was experimentally investigated at 25°C and 1 atm. Both Y and Ho were observed to be strongly partitioned into the overgrowths of calcite or aragonite. Their partition coefficients, D_Y and D_Ho, were determined to be ∼520-1400 and ∼700-1900 in calcite, ∼1200-2400 and ∼2400-4300 in aragonite, respectively. Y fractionates from Ho during the coprecipitation with either calcite or aragonite. Within our experimental conditions, the fractionation factor, k = D_Y/D_Ho, was determined to be ∼0.62-0.77 in calcite and ∼0.50-0.57 in aragonite, respectively. The aqueous complexation of Y and Ho, which is a function of solution chemistry, probably plays an important role in both the partitioning and the fractionation. Further analyses suggest that the difference in covalency between Y and Ho associated with changes in their coordination environments is the determinant factor to the Y-Ho fractionation in the H₂CO₃-CaCO₃ system.

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The Cretaceous-Tertiary (K-T) boundary about 65 million years ago records a mass extinction event caused by a bolide impact. K-T boundary clay collected from Stevns Klint, Denmark was investigated in this work. Iridium concentrations of eight clays across the K-T boundary were determined using a multiple gamma-ray analysis system after neutron activation. Anomalously high Ir concentrations were detected in five marl samples, with the highest concentration being 29.9 ppb. Four samples were analyzed for all noble gases. No extraterrestrial Ar, Kr, and Xe were discovered in any of the samples, although most of the ³He which was detected was extraterrestrial. Solar-like Ne was observed only in the sample SK4, which had an Ir concentration of 14.3 ppb, indicating the presence of micrometeorites. The solar-like Ne clearly did not originate from an asteroid/comet associated with the bolide impact, as that asteroid is thought to have been extremely large. Also, because there was no sign of a high accretion rate of micrometeorites at the boundary it could not be ascertained whether the solar-like Ne was related to a catastrophic event that led to the extinction of the dinosaurs.

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Rapid industrialization and economic take-off in coastal cities of China have placed great strain on the environment. In the this study, 40 aerosol samples were collected in the coast of Xiamen, Fujian province, west Taiwan Strait, P. R. China, from January to December 2003. The samples were analysed for the concentrations of elements (K, Ca, Na, Zn, Pb, W, Se, As, Ni, Ba, Nb, Ta, Zr, Hf, Th, U, Sr, REEs, etc.). All the elements display significant seasonal variations. The concentrations of most of the elements (except Na and Se) were high in January and February, abruptly decreased in March, kept relatively constant but low from April to August, and then gradually increased from September to December. This corresponds to the rainless climate and the influence of biomass burning from Southeast Asia in the winter and rain scavenging and the diffusion of typhoon in the summer. Thus, most of the elements have a good negative correlation with the monthly precipitation. The SEM/EDX studies indicate that the aerosols of Xiamen mainly consisted of soot grains, clay minerals, feldspar, gypsum, quartz, and biological particulates. The calculated enrichment factors indicate that Na and Br are derived from ocean, Pb, Zn, As, Sb, Se, W, and Ni are anthropogenic elements mainly derived from coal combustion, vehicle exhaust, and mining, and the other elements (i.e., Zr, Fe, Cr, Co, Rb, Sr, Cs, Ba, Hf, Ta, Th, U, and REEs) are crustal elements derived from weathered rocks and soil dust. The elemental concentrations of aerosols in Xiamen were compared with other cities, and the results indicate that Xiamen, like other coastal cities such as Qingdao, Dalian, Hong Kong, and Tokyo, has much lower concentrations of the elements such as Pb, Zn, and Cr than Beijing. The elemental deposition fluxes in Xiamen were also compared to other cities. The comparisons indicate that the elemental deposition fluxes in these cities are influenced not only by climatic characteristics (e.g., the precipitation and the sandstorm), but also by the industrial facility denseness.

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We studied deuterium-to-hydrogen isotope effects in aqueous hydroxide ion at the HF/6-31G(d) and B3LYP/6-31+G(d) levels of theory, using OH^-(H₂O)₃₉ clusters as model systems. Both the theoretical levels indicated that the hydroxide hydrogen atom and hydrogen atoms of waters hydrogen-bonded to the hydroxide oxygen atom tended to be depleted in the heavier hydrogen isotope relative to hydrogen atoms of bulk water and the degree of deuterium depletion was more substantial in the former than in the latter hydrogen atoms.

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Due to its potential as a paleoredox proxy, there have been many studies on Mo isotopic fractionation during adsorption onto ferromanganese oxides in seawater. However, the mechanisms of both adsorption and isotopic fractionation are still under debate due to the lack of structural information on the adsorbed species. In this study, XAFS analyses were performed to reveal the mechanism, based on structural information at the molecular level, of Mo isotopic fractionation during adsorption onto ferromanganese oxides. Molybdenum L₃-edge XANES and K-edge EXAFS revealed that Mo species adsorbed on the surface of ferrihydrite was a tetrahedrally coordinated outer-sphere complex, while that on δ-MnO₂ was an octahedrally coordinated inner-sphere complex. Additionally, it was also revealed that δ-MnO₂ was the dominant host phase of Mo in the hydrogenetic ferromanganese nodules from the comparison of their XAFS spectra. Previous studies reported that lighter isotopes of Mo were preferentially incorporated into ferromanganese oxides from seawater. This fractionation can be explained based on the structural difference between tetrahedral MoO₄^2- (=a major species in seawater) and the octahedral species adsorbed on the Mn oxide phase in ferromanganese nodules. In contrast, little change in Mo local structures during its adsorption onto ferrihydrite also suggested the little or no fractionation of Mo isotopes in the presence of Fe hydroxides without Mn oxides. These facts imply that the Mo isotopic composition in ancient marine sediments can distinguish redox boundaries of Fe²⁺/Fe(OH)₃ and of the more oxic Mn²⁺/MnO₂.

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Clays and clay rocks are considered viable geotechnical barriers in radioactive waste disposal. One reason for this is the propensity for cation exchange reactions in clay minerals to retard the migration of radionuclides. Although another retardation mechanism, namely the incorporation of radionuclides into sulfate or carbonate solid solutions, has been known for a long time, only recently has it been examined systematically. In this work, we investigate the competitive effect of both mechanisms on the transport of radium (Ra) in the near-field of a low- and intermediate level nuclear waste repository. In our idealized geochemical model, numerical simulations show that barium (Ba) and strontium (Sr) needed for Ra sulfate solid solutions also partition to the cation exchange sites of montmorillonite (Mont), which is the major mineral constituent of bentonite that is used for tunnel backfill. At high Mont content, most Ra tends to attach to Mont, while incorporation of Ra in sulfate solid solutions is more important at low Mont content. To explore the effect of the Mont content on the transport of radium, a multi-component reactive transport model was developed and implemented in the scientific software OpenGeoSys-GEM. It was found that a decrease of fixation capacity due to low Mont content is compensated by the formation of solid solutions and that the migration distance of aqueous Ra is similar at different Mont/water ratios.

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