Surface complexation modeling of Uranium(VI) sorption on quartz in the presence and absence of alkaline earth metals

Surface complexation models (SCMs) are widely utilized as a tool to study the mobility of radionuclide to the environment. In this study, two SCMs, electrostatic (ES) and non-electrostatic (NES) models are employed in order to simulate the sorption behavior of U(VI) on quartz in the absence of Mg, Ca, and Sr and ES model in the presence of alkaline earth metals. The surface reaction constants (log K) for ES and NES models were fitted to experimental data by coupling PEST with PHREEQC. The SCM prediction of U(VI) sorption on quartz in the absence of alkaline earth metals is in good agreement with the experimental data in the pH range 6.5–9. The estimated log K values are sensitive to both ES and NES model calculations. In U(VI)-Mg-quartz, U(VI)-Ca-quartz, and U(VI)-Sr-quartz systems, only the ES model shows the general trend of the experimental data. The estimated log K values are sensitive with respect to the surface reactions. Hence, the ES model is more suitable for model calculations of the U(VI)-Mg-quartz, U(VI)-Ca-quartz, and U(VI)-Sr-quartz systems.     

Estimation of groundwater recharge using a GIS-based distributed water balance model in Dire Dawa, Ethiopia

Sustainable groundwater management requires knowledge of recharge. Recharge is also an important parameter in groundwater flow and transport models. Spatial variation in recharge due to distributed land-us.e, soil texture, topography, groundwater level, and hydrometeorological conditions should be accounted for in recharge estimation. However, conventional point-estimates of recharge are not easily extrapolated or regionalized. In this study, a spatially distributed water balance model WetSpass was used to simulate long-term average recharge using land-use, soil texture, topography, and hydrometeorological parameters in Dire Dawa, a semiarid region of Ethiopia. WetSpass is a physically based methodology for estimation of the long-term average spatial distribution of surface runoff, actual evapotranspiration, and groundwater recharge. The long-term temporal and spatial average annual rainfall of 626 mm was distributed as: surface runoff of 126 mm (20%), evapotranspiration of 468 mm (75%), and recharge of 28 mm (5%). This recharge corresponds to 817 l/s for the 920.12 km² study area, which is less than the often-assumed 1,000 l/s recharge for the Dire Dawa groundwater catchment.     

Olivine intergranular plasticity at mantle pressures and temperatures

The ductile behavior of olivine-rich rocks is critical to constrain thermal convection in the Earth's upper mantle. Classical olivine flow laws for dislocation or diffusion creep fail to explain the fast post-seismic surface displacements observed by GPS, which requires a much weaker lithosphere than predicted by classical laws. Here we compare the plasticity of olivine aggregates deformed experimentally at mantle pressures and temperatures to that of single crystals and demonstrate that, depending on conditions of stress and temperature, strain accommodated through grain-to-grain interactions – here called intergranular strain – can be orders of magnitude larger than intracrystalline strain, which significantly weakens olivine strength. This result, extrapolated along mantle geotherms, suggests that intergranular plasticity could be dominant in most of the upper mantle. Consequently, the strength of olivine-rich aggregates in the upper mantle may be significantly lower than predicted by flow laws based on intracrystalline plasticity models.     

地下水中铀的反应运移模拟

地下水中铀的反应运移模拟对地下水保护和铀矿区的恢复都很重要, 因为铀是一种化学毒害性很高的放射性元素.在地下水及水与固体之间都应考虑对流、弥散、稀释、吸附等化学相互作用.介绍了德国德累斯顿市附近的Koenigstein矿区淋滤条件的可行性研究结果.由于反应运移模拟需占用大量的CPU时间, 所有的运行在一天内完成, 但用简单的混合法进行了稀释.对于这种研究, PHREEQC 2.2证明是一个功能很强的工具.与PHREEQC相对应的数据库WATEQ4F涉及到48种元素、400多种物质、300多种矿物.根据铀和镭的特性, 对其作了一定的修改, 以使它更具相容性和可靠性.      

Structural and mineralogical study of active and inactive hydrothermal fluid discharges in Panarea,Italy

The isle of Panarea (Aeolian Arc, Italy) is an active hydrothermal system, characterized by different types of fluid emissions, which cause various types of unique hydrothermal structures that are typical for hydrothermal fluid discharges. Such fluid discharge structures at shallow depths of less than 30 m have not been described in marine hydrothermal systems until now to the authors’ knowledge. The focus of the investigations was set on morphological, mineralogical, geochemical, and structural analyses. A broad variety of analytical methods was applied to gain as much information as possible. In addition to geological and sedimentological documentation and standard methods like making and analyzing thin and polished sections, optical microscopy or X-ray fluorescence analysis, the samples were investigated by X-ray computer tomography and scanning electron microscopy, including energy-dispersive X-ray spectroscopy. Because discharge features occur in various settings, a general classification of the features in the hydrothermal system was performed with special focus on their preservability in geological archives. In total, nine different facies types were distinguished based on genetic and/or morphological differences. All samples show laminated structures from µm to cm scale. The single laminae vary in shape and material witnessing various chemical compositions.     

Application of Landsat 5 and Landsat 7 images data for water quality mapping in Mosul Dam Lake,Northern Iraq

Mosul Dam Lake is the main reservoir in Iraq, supporting the water demand of Mosul, Baghdad, and other cities. The aim of this study is to derive simple and accurate algorithms for the retrieval of water quality parameters for Mosul Dam Lake from Landsat 5 and Landsat 7 reflectance data. The water quality measurements were performed in situ during March and July 2011. These measurements included temperature, turbidity, Secchi disk, chlorophyll-a, nitrate, nitrite, phosphate, total inorganic carbon, dissolved organic carbon, total dissolved solids, and pH. In order to properly use the values of reflectance bands, images enhancement techniques have been used. The field measurements were compared with reflectance values of Landsat 5 and Landsat 7 bands using different band combination of empirical algorithms. Generally, the results of analysis showed significant correlation between these models and water quality parameters with R ²?>?0.7 and p?R ²?>?0.9 and p?R ²?>?0.9, and values of the root mean square error ranged from 0.9 to 0.001. ArcGIS 10 was used to simulate the distribution values of water quality parameters calculated from spectral values of TM5 and ETM+ bands. The results of spatial analysis demonstrate that it is possible to use the TM5 and ETM+ images to evaluate the water quality for Mosul Dam Lake.     

Effect of Microbial Siderophore DFOB on Pb, Zn, and Cd Sorption Onto Zeolite

Recent studies suggest that siderophores form stable complexes with divalent metals and affect their mobility. In this work, effects of trihydroxamate microbial siderophores and desferrioxamine-B (DFOB) on Pb(II), Zn(II), and Cd(II) sorption by two kinds of synthesized zeolites (13X and Na?CY) as a function of pH were investigated. Results showed that 13X zeolite has a higher sorption affinity for studied metals than Na?CY. DFOB strongly affected metal sorption on both zeolites. Under slightly acidic to neutral condition, DFOB increased the metal sorption on zeolites due to the sorption of positively charged heavy metal?CDFOB complexes. Whereas by increasing pH (>7), the mobilizing effect of DFOB was observed for Pb, Zn, and Cd. DFOB drastically decreased (80?%) Zn sorption in alkaline condition. As a result, siderophores can weaken the treatment efficiency of zeolites and increase the bioavailability of metals in soils. Surface complexation modeling revealed that the effects of DFOB on metal sorption by 13X and Na?CY zeolites can be explained by the differences in their surface charge. In general, the result shows the influence of DFOB on metal sorption by zeolites over the pH range 4?C9 and decreasing in the sequence Zn?>?Pb?>?Cd.     

The cloud imaging and particle size experiment on the aeronomy of ice in the mesosphere mission: Cloud morphology for the northern 2007 season

The Aeronomy of Ice in the Mesosphere (AIM) mission was launched from Vandenberg Air Force Base in California at 4:26:03 EDT on April 25, 2007, becoming the first satellite mission dedicated to the study of noctilucent clouds (NLCs), also known as polar mesospheric clouds (PMC) when viewed from space. We present the first results from one of the three instruments on board the satellite, the Cloud Imaging and Particle Size (CIPS) instrument. CIPS has produced detailed morphology of the Northern 2007 PMC and Southern 2007/2008 seasons with 5 km horizontal spatial resolution. CIPS, with its very large angular field of view, images cloud structures at multiple scattering angles within a narrow spectral bandpass centered at 265 nm. Spatial coverage is 100% above about 70° latitude, where camera views overlap from orbit to orbit, and terminates at about 82°. Spatial coverage decreases to about 50% at the lowest latitudes where data are collected (35°). Cloud structures have for the first time been mapped out over nearly the entire summertime polar region. These structures include ‘ice rings’, spatially small but bright clouds, and large regions (‘ice-free regions’) in the heart of the cloud season essentially devoid of ice particles. The ice rings bear a close resemblance to tropospheric convective outflow events, suggesting a point source of mesospheric convection. These rings (often circular arcs) are most likely Type IV NLC (‘whirls’ in the standard World Meteorological Organization (WMO) nomenclature).     

Lattice preferred orientation in CaIrO<Subscript>3</Subscript> perovskite and post-perovskite formed by plastic deformation under pressure

Lattice preferred orientations (LPO) developed in perovskite and post-perovskite structured CaIrO₃ were studied using the radial X-ray diffraction technique combined with a diamond anvil cell. Starting materials of each phase were deformed from 0.1 MPa to 6 GPa at room temperature. Only weak LPO was formed in the perovskite phase, whereas strong LPO was formed in the post-perovskite phase with an alignment of the (010) plane perpendicular to the compression axis. The present result suggests that the (010) is a dominant slip plane in the post-perovskite phase and it is in good agreement with the crystallographic prediction, dislocation observations via transmission electron microscopy, and a recent result of simple shear deformation experiment at 1 GPa–1,173 K. However, the present result contrasts markedly from the results on MgGeO₃ and (Mg,Fe)SiO₃, which suggested that the (100) or (110) is a dominant slip plane with respect to the post-perovskite structure. Therefore it is difficult to discuss the behavior of the post-perovskite phase in the Earth’s deep interior based on existing data of MgGeO₃, (Mg,Fe)SiO₃ and CaIrO₃. The possible sources of the differences between MgGeO₃, (Mg,Fe)SiO₃ and CaIrO₃ are discussed.