首页期刊导航|Chemical geology
期刊信息/Journal information
Chemical geology
Elsevier
Chemical geology

Elsevier

0009-2541

Chemical geology/Journal Chemical geologySCIISTPAHCIEI
正式出版
收录年代

    Evaluation of environmental radioactivity in soils around a coal burning power plant and a coal mining area in Barapukuria, Bangladesh: Radiological risks assessment

    Habib, Md AhosanKhan, RahatPhoungthong, Khamphe
    13页
    查看更多>>摘要：To study the distributions and potential dispersions of naturally occurring radioactive materials (NORMs: Ra-226, Th-232, and K-40) from coal-based activities (Barapukuria, Bangladesh), we studied a suite of systematically collected surface and sub-surface soil samples by X-ray fluorescence and high purity germanium detector based gamma-spectroscopy. The average (range) radioactivities of Ra-226, Th-232, and K-40 in the studied soil samples were 80.6 (33.0-118.0), 104.4 (43.0-182.0), and 508.1 (318.3-743.4) Bq.kg(-1), respectively, which are significantly higher than the corresponding world average value. No significant fractionations of NORMs were observed between the surface and sub-surface soils, except for Th-232. Along with the anthropogenic origin, several geochemical processes (e.g., weathering, mineralogical dissolution/precipitation, alteration, leaching, differential solubility mediated geochemical mobility etc.) play significant role in NORM distributions. Major-oxide abundances, indices-based calculations, and correlation studies on the measured parameters revealed the natural processes (e. g., geochemical mobility, mineralogical distributions, water logging based differential solubility) responsible for NORM distributions. In terms of mean radium equivalent activity, internal hazard index, and total annual effective dose values, the studied area possesses trivial radiological risks, whereas the values of internal absorbed gamma dose and excess lifetime cancer risk demonstrate significant health hazards. Considering the adverse radiological risks originating from coal-based industrial activities and the long half-lives of NORMs, the present scenario will potentially be deteriorated.
      原文链接:
    • NSTL
    • Elsevier

    Thermodynamic and spectroscopic investigations of Shewanella putrefaciens CN32 cell envelope

    Wray, AddienGorman-Lewis, Drew
    12页
    查看更多>>摘要：A quantitative understanding of prokaryotic cell envelope reactivity is necessary to accurately describe the surface complexation reactions known to impact metal transport in the subsurface. The gram-negative bacterium Shewanella putrefaciens CN32 (CN32) has been the focus of previous cell envelope studies in large part due to its ability to directly influence iron and uranium geochemistry; however, important gaps remain in our understanding of reactions occurring on its cell envelope. Combining surface complexation modeling of potentiometric titration data with isothermal titration calorimetry provides an additional method to evaluate how well surface complexation models (SCMs) represent cell envelope reactivity. It also gives us the ability to determine sitespecific enthalpies and entropies of protonation, which can aid both in site structure identification and description of conformational changes to those sites, further improving our understanding of the CN32 cell envelope. We gathered potentiometric and isothermal calorimetric titration data of CN32 over a range of ionic strength (0.02 - 0.53 M) while monitoring cell viability and performing Fourier transform infrared spectroscopy (FTIR) investigations. FTIR analysis was performed over a range of pH (4 - 9.4) to confirm identification of proton-active sites. Surface complexation modeling revealed that models involving 3 and 4 sites could adequately describe the potentiometric titration data; however, a 3-site model best represented the calorimetric data. We inferred the following site identities based on characteristic enthalpies, entropies, and equilibrium constants of protonation: carboxyl (log(K): 4.79 - 4.95), phosphoryl (6.69 - 6.97), and amine groups (9.37 - 9.64). Spectral corroboration via FTIR indicated the presence of chemical moieties consistent with these functional group assignments. Ionic strength was shown to have a significant impact on the concentration of all three sites at 95% confidence. Entropies and equilibrium constants of protonation for carboxyl and phosphoryl sites did not significantly change with ionic strength. For the carboxyl group, enthalpies of protonation varied significantly between the lowest and highest ionic strengths examined, though enthalpies at intermediate concentrations were not distinguishable. Enthalpies of protonation for the amine group were statistically different at each ionic strength. Additionally, entropies and equilibrium constants of protonation for the amine group were significantly affected by all ionic strengths tested. The entropy of protonation for the amine site changed from -21.5 +/- 6.1 to +109.0 +/- 4.2 J/molK- 1 as ionic strength increased from 0.02 to 0.53 M, respectively. A change in the entropy of protonation of this magnitude and sign is indicative of a substantial conformational change in this functional group. Cell viability was significantly impacted over the course the titrations; however, viability did not impact SCMs results. In sum, these data fill gaps in our understanding of CN32 and provide new insights into the intricacies of its cell envelope.
      原文链接:
    • NSTL
    • Elsevier

    Mica trace-element signatures: Highlighting superimposed W-Sn mineralizations and fluid sources

    Bailly, LaurentBeziat, DidierDe Parseval, PhilippeMonnier, Lois...
    22页
    查看更多>>摘要：In the Echassieres district of the French Massif Central, occur several outstanding magmatic/hydrothermal systems enriched in strategic metals, such as the Beauvoir rare-metal granite. In this contribution we propose a systematic approach, based on mica trace chemistry, to decipher the different events leading to mineralization. Twelve groups of micas were defined by their specific petrographic features and/or location in the district. Their trace element composition, obtained by LA-ICP-MS, varies widely from one mica group to another, although homogeneous signatures within groups could be distinguished. Some of the trace elements are remarkably enriched, such as W in igneous lepidolite and Sn in greisen muscovite, both of which occur in the Beauvoir granite. A statistical approach based on a set of multivariate analyses highlights that the trace chemistry of micas is inherited from their source, whether hydrothermal or igneous, thus providing a signature for their origin. This approach also shows that differences in major element composition (i.e., different mica species) impact only slightly the trace-element signature. For instance, muscovite and zinnwaldite from one granite have a coherent signature, but they contrast with same mica species in another granite or hydrothermal veins. It is thus possible to genetically link two different mica species from remote locations, or inversely, to recognize different origins for a same mica species in the same sample (e.g., superposed alterations). A second, important implication is that trace-element signatures of micas provide a record of metal remobilization and transport. In the Echassieres district, greisen alteration of the Beauvoir granite caused dissolution of W-rich (ca. 290 ppm in average) lepidolite and cassiterite (SnO2). Newly-formed greisen muscovite incorporated most remobilized Sn (ca. 1000 ppm in average), while W precipitated in distal quartz veins as wolframite. As a consequence, Sn is concentrated in the granite, while W occurs outside of it. This is also underlined by the gradual Sn decrease and W increase recorded in micas from distal veins. Finally, wolframite-bearing veins do not contain cassiterite, validating mica trace-element chemistry as a powerful tool to decipher Sn-W ore forming hydrothermal processes.
      原文链接:
    • NSTL
    • Elsevier

    Dynamics of coupled olivine dissolution and serpentine precipitation revealed by hydrothermal flow-through experiments at 260 degrees C-300 degrees C

    Oyanagi, RyosukeKuwatani, TatsuSuzuki, Katsuhiko
    11页
    查看更多>>摘要：Serpentinization is an important process that influences rock rheology, global fluid circulation, and microbiological activity in the deep sea, and is induced by hydrothermal fluid flow. Elemental olivine dissolution and serpentine precipitation govern the overall dynamics of serpentinization, and its prediction and modeling require an understanding of the reaction mechanism including the rate-limiting process. In this study, we examined the initial stage of coupled olivine dissolution and serpentine precipitation at 260 degrees C-300 degrees C and 50 MPa using a hydrothermal flow-through experimental apparatus. Saline water (0.5 m NaCl) was continuously injected into olivine powder at a constant flow rate (3.3 x 10(-5) L s(-1)). Petrologic observation of solid products after experimental runs revealed that serpentine is produced from olivine. The hydration flux of serpentinization in this experiment is similar to estimates made using closed-system experiments, indicating that fluid flow does not affect the hydration rate at the flow rates adopted. Moreover, mass-balance calculations based on outlet fluid compositions during experiments suggest that both the overall serpentine precipitation and olivine dissolution rates decrease over time, and the serpentine precipitation rate is lower than the olivine dissolution rate during serpentinization. Although a comparison of speciated solutions observed in this experiment with results obtained by kinetic reaction modeling did not constrain the relationship between serpentine precipitation and olivine dissolution, a comparison with other experimental data and kinetic modeling results indicates that serpentine precipitation occurs more slowly than olivine dissolution at 170 degrees C. These results suggest that the relationship between serpentine precipitation and olivine dissolution kinetics varies with temperature and time, with such dynamic behavior governing serpentinization processes in the oceanic crust.
      原文链接:
    • NSTL
    • Elsevier

    A potential linkage between excess silicate-bound nitrogen and N-2-rich natural gas in sedimentary reservoirs

    Liu, YangStueken, Eva E.Wang, DongshengNie, Haikuan...
    10页
    查看更多>>摘要：Molecular nitrogen (N-2) released from sedimentary rocks during metamorphism is an important component of the biogeochemical nitrogen cycles. However, the importance and variability of this metamorphic N-2 flux from rock nitrogen to Earth's surface environment remains largely unexplored. Here we present a comprehensive bulk rock C-N and N-2 concentration dataset from the lower Cambrian shale across the Yangtze Block. The results reveal a spatial trend of excess silicate-bound nitrogen in the lower Cambrian shale throughout the Yangtze Block, which is interpreted as partial assimilation of ammonium (NH4+ ) with high concentrations of NH4+ accumulating in the euxinic water column and in sediment pore waters at shelf and slope environments during sedimentation. The remarkable spatial coupling between silicate-bound nitrogen in bulk rock shale and N-2 concentration in modern shale reservoirs indicates that the high proportion of silicate-bound nitrogen may act as an important control on the formation of N-2-rich gas in shale reservoirs during metamorphism. These N-2-rich reservoir rocks may have affected the surface environment through tectonic movement over Earth's history. Our results therefore identify a novel linkage in the nitrogen cycle and provide evidence for the importance of metamorphism on the return of rock nitrogen back to the surface environment. We further reveal that the metamorphic N-2 gas flux from the geosphere to the atmosphere is dependent on environmental conditions during sediment deposition.
      原文链接:
    • NSTL
    • Elsevier

    Effect of growth rate on nickel and cobalt incorporation in aragonite

    Brazier, Jean-MichelMavromatis, Vasileios
    12页
    查看更多>>摘要：The incorporation of Ni and Co in aragonite was experimentally investigated as a function of mineral growth rate using the constant addition technique at 25 degrees C and 1 bar pCO(2). The distribution coefficients of Ni and Co (i.e., D-Me = (Me/Ca)(solid)/(a(Me)(2+)/a(Ca)(2+))(fluid)) exhibit a linear correlation with mineral growth rate in the range -9.1 <= Log r(p) <= -7.5 mol/m(2)/s. The obtained results suggest a stronger dependency of D(Ni )to growth rate compared to that observed for D-Co. These dependencies can be described as: Log D-Ni = 1.247 (+/- 0.152) Log r(p) + 7.448 (+/- 1.212); R-2 = 0.82 Log D-Co = 0.312 (+/- 0.047) Log r(p) + 1.664 (+/- 0.383); R-2 = 0.81 The DMe-aragonite values for both Ni and Co are systematically lower than unity and their increase with increasing growth rate is in agreement with the incorporation of elements incompatible with the host mineral structure. Using the dependency of D-Ni and D-Co to the saturation indices (SI) of the reactive solution with respect to aragonite, the D-Me under equilibrium were estimated. These estimates yield equilibrium Log D-Me values of -3.9 and - 1.0 for Ni and Co, respectively. These experimentally defined D(eq )values are 1.3 to 4.3 orders of magnitude lower compared to theoretical estimates that were earlier published in the literature. Similar to other incompatible elements, the observed increase of D(Ni )and D-Co values with degree of saturation, points towards incorporation related to the density of defect sites on the mineral surface. Finally, the dependencies recorded in this study suggest that D-Ni and D-Co have the potential to be used as a proxy for saturation degree of the reactive solution.
      原文链接:
    • NSTL
    • Elsevier