Complexation of Cu in Hydrothermal NaCl Brines: Ab initio molecular dynamics and energetics

Chloride complexation of Cu⁺ controls the solubility of copper(I) oxide and sulfide ore minerals in hydrothermal and diagenetic fluids. Solubility measurements and optical spectra of high temperature CuCl solutions have been interpreted as indicating the formation of CuCl, , and complexes. However, no other monovalent cation forms tri- and tetrachloro complexes. EXAFS spectra of high temperature Cu-Cl solutions, moreover, appear to show only CuCl and complexes at T > 100 °C. To reconcile these results, I investigated the nature and stability of Cu-Cl complexes using ab initio cluster calculations and ab initio (Car-Parrinello) molecular dynamics simulations for CuCl-NaCl-H₂O systems at 25 to 450 °C. Ab initio molecular dynamic simulations of 1 m CuCl in a 4 m Cl solution give a stable complex at 25 °C over 4 ps but show that the third Cl⁻ is weakly bound. When the temperature is increased along the liquid-vapour saturation curve to 125 °C, the complex dissociates into and Cl⁻; only forms at 325 °C and 1 kbar. Even in a 15.6 m Cl brine at 450 °C, only the complex forms over a 4 ps simulation run.Cluster calculations with a static dielectric continuum solvation field (COSMO) were used in an attempt directly estimate free energies of complex formation in aqueous solution. Consistent with the MD simulations, the complex is slightly stable at 25 °C but decreases in stability with decreasing dielectric constant (ε). The complex is predicted to be unstable at 25 °C and becomes increasingly unstable with decreasing dielectric constant. In hydrothermal fluids (ε < 30) both the and complexes are unstable to dissociation into and Cl⁻.The results obtained here are at odds with recent equations of state that predict and complexes are the predominant species in hydrothermal brines. In contrast, I predict that only complexes will be significant at T > 125 °C, even in NaCl-saturated brines. The high-temperature (T > 125 °C) optical spectra of CuCl solutions and solubility measurements of Cu minerals in Cl-brines need to be reinterpreted in terms of only the CuCl and complexes.     

Boric acid adsorption on humic acids: Ab initio calculation of structures, stabilities, B NMR and B,B isotopic fractionations of surface complexes

Boric acid, B(OH)₃, forms complexes in aqueous solution with a number of bidentate O-containing ligands, HL⁻, where H₂L is C₂O₄H₂ (oxalic acid), C₃O₄H₄ (malonic acid), C₂H₆O₂ (ethylene glycol), C₆H₆O₂ (catechol), C₁₀H₈O₂ (dioxynaphthalene) and C₂O₃H₄ (glycolic acid). McElligott and Byrne [McElligott, S., Byrne, R.H., 1998. Interaction of and in seawater: Formation of . Aquat. Geochem.3, 345-356.] have also found B(OH)₃ to form an aqueous complex with . Recently Lemarchand et al. [Lemarchand, E., Schott, J., Gaillardeet, J., 2005. Boron isotopic fractionation related to boron sorption on humic acid and the structure of surface complexes formed. Geochim. Cosmochim. Acta69, 3519-3533] have studied the formation of surface complexes of B(OH)₃ on humic acid, determining ¹¹B NMR shifts and fitted values of formation constants, and ¹¹B, ¹⁰B isotope fractionations for a number of surface complexation models. Their work helps to clarify both the nature of the interaction of boric acid with the functional groups in humic acid and the nature of some of these coordinating sites on the humic acid. The determination of isotope fractionations may be seen as a form of vibrational spectroscopy, using the fractionating element as a local probe of the vibrational spectrum. We have calculated quantum mechanically the structures, stabilities, vibrational spectra, ¹¹B NMR spectra and ¹¹B,¹⁰B isotope fractionations of a number of complexes B(OH)₂L⁻ formed by reactions of the type:

     

Prediction of equilibrium Li isotope fractionation between minerals and aqueous solutions at high P and T: An efficient ab initio approach

The mass-dependent equilibrium stable isotope fractionation between different materials is an important geochemical process. Here we present an efficient method to compute the isotope fractionation between complex minerals and fluids at high pressure, P, and temperature, T, representative for the Earth’s crust and mantle. The method is tested by computation of the equilibrium fractionation of lithium isotopes between aqueous fluids and various Li bearing minerals such as staurolite, spodumene and mica. We are able to correctly predict the direction of the isotope fractionation as observed in the experiments. On the quantitative level the computed fractionation factors agree within 1.0‰ with the experimental values indicating predictive power of ab initio methods. We show that with ab initio methods we are able to investigate the underlying mechanisms driving the equilibrium isotope fractionation process, such as coordination of the fractionating elements, their bond strengths to the neighboring atoms, compression of fluids and thermal expansion of solids. This gives valuable insight into the processes governing the isotope fractionation mechanisms on the atomic scale. The method is applicable to any state and does not require different treatment of crystals and fluids.     

Uncertainty propagation in geochemical calculations: non-linearity in solubility equilibria

Uncertainty in the results of geochemical equilibrium calculations may be estimated from input uncertainties using either derivative approximations or Monte Carlo simulations. While derivative methods are fast and convenient for many equilibria, inherently non-linear aspects of solubility equilibria may lead to a failure of the linear approximation and thus to asymmetric and/or bimodal uncertainty in calculated concentrations. In these cases, the use of derivative methods and the assumption of Gaussian uncertainty in the calculated concentrations misrepresent the propagated uncertainty. Equilibria with gibbsite, calcite, and the chromate analog of jarosite are examined.     

Thermodynamic model for arsenic speciation in sulfidic waters: A novel use of ab initio computations

Recent discoveries demonstrate that the chemistry of arsenic in sulfidic waters is much more complex that previously believed. One implication is that all earlier thermodynamic data on stabilities of As thioanions require revision. Previously used experimental approaches for determining As thioanion stabilities may be inadequate to deal with the full range of complexity. Here we use computational as well as empirical information to construct a provisional model for equilibrium As thioanion distributions in sulfidic waters. Whereas previous authors have argued for either As(III) or As(V) thioanions, the new model predicts that both are important and can occur simultaneously under commonly encountered pH and ΣS^−II conditions. At the order of magnitude level, the model reasonably predicts the solubility of As₂S₃ in sulfidic solutions, provides tentative peak assignments for published Raman spectroscopic data and plausibly accounts for how sulfide modifies the bacterial toxicity of As. The model yields a thermodynamic justification for how sulfide, which is usually regarded as a reducing agent, can counter-intuitively drive oxidation of As(III) to As(V), as has been observed both in the laboratory and in the field. Despite its uncertain accuracy, the model serves as a useful source of new, testable hypotheses about As geochemistry and highlights crucial experimental data needs.     

Computer modeling of natural silicate melts: What can we learn from ab initio simulations

The structural and dynamical properties of four silicate liquids (silica, rhyolite, a model basalt and enstatite) are evaluated by ab initio molecular dynamics simulation using the density functional theory and are compared with classical simulations using a simple empirical force field. For a given composition, the structural parameters of the simulated melt vary little between the two calculations (ab initio versus empirical) and are in satisfactory agreement with structure data available in the literature. In contrast, ionic diffusivities and atomic vibration motions are found to be more sensitive to the details of the interactions. Furthermore, it is pointed out that the electronic polarization, as evaluated by the ab initio calculation, contributes significantly to the intensity of the infrared absorption spectra of molten silicates, a spectral feature which cannot be reproduced using nonpolarizable force field. However the vibration modes of TO₄ species and some structural details are not accurately reproduced by our ab initio calculation, shortcomings which need to be improved in the future.     

Water dissolution in albite melts:: Constraints from ab initio NMR calculations

Hartree-Fock and B3LYP NMR calculations were performed at the 6-311+G(2df,p) level on cluster models representing albite glasses using B3LYP/6 to 31G* optimized geometries. Calculation results on several well-known crystalline materials, such as low albite and KHSi₂O_5, were used to check the accuracy of the calculation methods.Calculated ²⁹Si-NMR results on clusters that model protonation of Al-O-Si linkages and the replacement of Na⁺ by H⁺ indicate a major increase in Si-O(H) bond length and a 5 ppm difference in δ_iso for ²⁹Si compared to that for anhydrous albite glass. The calculated δ_iso of ²⁷Al in such linkages agrees with the experimental data, but shows an increase in C_q that cannot be fully diminished by H-bonding to additional water molecules. This protonation model is consistent with both experimental ¹⁷O NMR data and the major peak of ¹H-NMR spectra. It cannot readily explain the existence of the small peak in the experimental ¹H spectra around 1.5 ppm. Production of the depolymerized units Al [Q³]-O-H upon the dissolution of water is not consistent with ²⁷Al, ¹H, or ¹⁷O NMR experimental results. Production of Si [Q³]-O-H is consistent with all of the experimental ¹⁷O and ¹H-NMR data; such units can produce both the major peak at 3.5 ppm and the small peak at 1.5 ppm in ¹H spectra, either with or without hydrogen bonding. This species, however, cannot produce the main features of ²⁹Si spectra.It is concluded that although neither protonation nor the production of Si [Q³]-O-H alone is consistent with the available experimental data, the combination of these two processes is consistent with available experimental NMR data.     

The dynamism of clustering: Interweaving material and discursive processes

The aim of this paper is to contribute to an understanding of clusters, including both the material and discursive dynamism of cluster construction, and shed light on how clusters—once established—affect the actors, institutions and processes that constitute them. It does this by viewing clusters as an actant, i.e. something that acts or to which activity is granted by others. The empirical analysis examines two clusters in the public cluster programme Norwegian Centre of Expertise (NCE): the Møre maritime cluster and the Hordaland subsea cluster. It focuses on the type of development paths they are following and how the material and discursive processes are interweaved in these paths. The clusters are related to the concept of cluster construction, which is triggered by ideas, representations, policy and industry practice. The Møre maritime cluster is characterized by bottom-up clustering processes and illustrates how the material practices of firms can trigger clustering processes such as the establishment of a cluster and the identification of a prototype of best cluster practice. On the other hand, the Hordaland subsea cluster expresses a top-down process and how the ideal world of academics and policy-making can encourage processes of clustering among co-located firms. Based on these observations of material and discursive interweaved clustering processes and how they affect both those who are practicing and those who are promoting them, we find it reasonable to argue for a stronger awareness of such feedback loops in cluster studies.     

Mass spectrometric and quantum chemical determination of proton water clustering equilibria

We report on the thermochemistry of proton hydration by water in the gas phase both experimentally using high-pressure mass spectrometry (HPMS) and theoretically using multilevel G3, G3B3, CBS-Q, CBS-QB3, CBS/QCI-APNO as well as density functional theory (DFT) calculations. Gas phase hydration enthalpies and entropies for protonated water cluster equilibria with up to 7 waters (i.e., n ? 7H₃O⁺·(H₂O)_n) were observed and exhibited non-monotonic behavior for successive hydration steps as well as enthalpy and entropy anomalies at higher cluster rank numbers. In particular, there is a significant jump in the stepwise enthalpies and entropies of cluster formation for n varying from 6 to 8. This behavior can be successfully interpreted using cluster geometries obtained from quantum chemical calculations by considering the number of additional hydrogen bonds formed at each hydration step and simultaneous weakening of ion-solvent interaction with increasing cluster size. The measured total hydration energy for the attachment of the first six water molecules around the hydronium ion was found to account for more than 60% of total bulk hydration free energy.     

A method for activity calculations in saline and mixed solvent solutions at elevated temperature and pressure: A framework for geological phase equilibria calculations

Quantitative thermodynamic calculations that involve aqueous fluids have proved difficult because of the complexity of the interactions that occur within the fluids. Existing thermodynamic models are difficult to apply to mixed solvent or highly saline solutions at P > 0.3 GPa and T > 300 °C. This work constructs a method for activity-composition calculations in saline, mixed solvent, supercritical aqueous solutions. Mixing is formulated on a mole-fraction scale in terms of a set of independent end-members that describe composition and speciation within the solution. The ideal mixing term takes speciation into account and avoids problems with the common ion effect. Non-ideal interactions are represented by an activity coefficient term that combines a limited form of Debye-Hückel and a van Laar formulation. This approach, referred to as the DH-ASF model, is thermodynamically valid over a wide range of P, T and fluid composition. The value of the model lies in its broad applicability, and small number of calibration parameters. Experimental data from the literature for the systems NaCl-H₂O, KCl-H₂O, H₂O-SiO₂-CO₂, H₂O-NaCl-CO₂, H₂O-NaCl-SiO₂ and for H₂O-albite melts have been used to calibrate the DH-ASF model. Calculations were performed using Thermocalc, computer software that calculates equilibria for mineral-based chemical systems.¹ The model represents the data to within experimental error in most cases. Conditions modelled include pressures between 0.2 and 1.4 GPa, temperatures between 500 and 900 °C, and x_H2O from 0.1 to 1. Calibrated parameters are consistent with expectations based on the conceptual model for the fluid, and are relatively insensitive to changes in pressure and temperature for most examples. The DH-ASF model is thermodynamically valid for a range of P-T conditions that includes pressures from 0.1 to 2 GPa and temperatures from 200 to 1000 °C. A lack of experimental data restricts calibration of the model for many end-members. However, it may be possible to neglect parameters associated with end-members present in small amount. In this case, or with new experimental data for calibrations, the DH-ASF model allows previously inaccessible geological systems and processes to be modelled.     

APL computer programs for thermodynamic calculations of equilibria in P-T-X CO 2 space

APL computer programs for the thermodynamic calculation of devolatilization and solid-solid equilibria operate using stored values for the molar volume and entropy of solids, the free energies of H₂O and CO₂, and the free energies of formation for 110 geologically-important phases. P-T-X _{CO 2} calculations of devolatilization equilibria can be made at pressures from 0.2 through 10 kb, and temperatures from 200 through 1,000° C. P-T-X calculations of solid-solid equilibria may be accomplished at pressures to 30 kb and temperatures to 1,000° C. Calculations can be extrapolations from experimental points, or direct calculations from thermochemical data alone. Options are available in these programs to consider effects of: real vs. ideal gas mixing, thermal expansion and compressibility, solid solution, fluid pressure differing from solid pressure, and uncertainties in high-temperature entropies.A collection of thermodynamic data programs accompanies the programs for calculating P-T-X _{CO 2} equilibria. Over a wide range of physical conditions, the data functions report free energies, entropies, fugacities of H₂O and CO₂, high temperature entropies of solids, and activities of components in H₂O-CO₂ mixtures.List of Symbols Activity of H₂O and CO₂ - G_f Free energy of formation of a phase from elements - G_r Free energy change of reaction - G _r ^o Standard state free energy change of a reaction - Free energies of pure H₂O and CO₂ - H _r ^o Standard state enthalpy change for a reaction - K Equilibrium constant - R Gas constant - S _r ^o Standard state entropy change of reaction - S _s ^o Standard state entropy change of solids in a reaction - V_s ^o Standard state volume change of a reaction - V_s ^o Standard state volume change of solids in a reaction - Mole fraction of H₂O and CO₂ - Activity coefficient of H₂O and CO₂     

掺Fe和V的金红石电子结构的第一性原理计算研究

采用基于密度泛函理论的第一性原理计算方法,对掺杂Fe和(或)V的金红石型TiO2的电子结构进行了计算。理论模拟的结果表明,纯金红石的禁带宽度为1.98 eV;Fe掺杂金红石型TiO2的禁带宽度为2.18 eV,由Fe3d和O2p轨道杂化在禁带中间形成了两条杂质能级;V掺杂金红石型TiO2的禁带宽度减小为1.80 eV,由V3d和O2p轨道杂化形成的杂质能级位于金红石的导带底,引入了一个浅施主能级;Fe和V共掺杂的金红石禁带中存在一个较宽的杂质能带,禁带宽度减小为1.73 eV。杂质能级的出现以及禁带宽度的减小使得Fe和V掺杂的金红石具有更好的可见光响应能力。同时,Fe和V的类质同像替代使得金红石中MO6八面体具有较大的畸变程度,有助于表面缺陷的增加,从而为光催化反应提供天然活性位。为进一步深入揭示含铁、钒等杂质的天然金红石的可见光催化机制提供了理论支持。     

Geochemical diversity in S processes mediated by culture-adapted and environmental-enrichments of Acidithiobacillus spp.

Coupled S speciation and acid generation resulting from S processing associated with five different microbial treatments, all primarily Acidithiobacillus spp. (i.e. autotrophic S-oxidizers) were evaluated in batch laboratory experiments. Microbial treatments included two culture-adapted strains, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans, their consortia and two environmental enrichments from a mine tailings lake that were determined to be >95% Acidithiobacillus spp., by whole-cell fluorescent hybridization. Using batch experiments simulating acidic mine waters with no carbon amendments, acid generation, and S speciation associated with the oxidation of three S substrates (thiosulfate, tetrathionate, and elemental S) were evaluated. Aseptic controls showed no observable pH decrease over the experimental time course (1 month) for all three S compounds examined. In contrast, pH decreased in all microbial treatments from starting pH values of 4 to 2 or less for all three S substrates. Results show a non-linear relationship between the pH dynamics of the batch cultures and their corresponding sulfate concentrations, and indicate how known microbial S processing pathways have opposite impacts, ultimately on pH dynamics. Associated geochemical modeling indicated negligible abiogenic processes contributing to the observed results, indicating strong microbial control of acid generation extending over pH ranges from 4 to less than 2. However, the observed acid generation rates and associated S speciation were both microbial treatment and substrate-specific. Results reveal a number of novel insights regarding microbial catalysis of S oxidation: (1) metabolic diversity in S processing, as evidenced by the observed geochemical signatures in S chemical speciation and rates of acid generation amongst phylogenetically similar organisms (to the genus level); (2) consortial impacts differ from those of individual strain members; (3) environmental enrichments of Acidithiobacillus spp. catalyze different S reaction arrays than pure strain Acidithiobacillus spp.; and (4) microbial catalysis of S reactions involves significant disproportionation tied to substantial H⁺ consumption, with the formation of as yet, poorly characterized intermediate S species, most likely polythionates and polysulfane monosulfonic acids that are thought to be involved in microbial S storage mechanisms.     

Biogeochemical processes in a clay formation in situ experiment: Part C - Organic contamination and leaching data

Data interpretation of the Porewater Chemistry (PC) experiment at the Mont Terri Rock Laboratory has led to unexpected observations of anaerobic microbial processes which caused important geochemical perturbations of the Opalinus Clay water in the borehole. The increases of acetate to 146 mg C/L, of DIC to 109 mg C/L and of CH₄ to 0.5 mg C/L were unexpected and could not be explained without the presence of a C source in the system. The organic C fuelling the observed microbial activity was until then unknown. Leaching tests were performed on several polymers used for the fabrication of the PC equipment to identify the source of organic matter (OM). Polyethylene (PE) appears to be very inert and does not release detectable concentrations of dissolved organic C (DOC) (<1 ppb) into the water. Polyurethane (PU) leaches out a dozen different organic compounds accounting for only 13 μg DOC/g PU. Under the conditions of the leaching tests, 1 g of polyamide (PA, Nylon) also releases ∼512 μg of the plasticizer N-Butyl-Benzene-Sulfonamide (NBBS). Soaking tests with polyethylene samples immersed in acetone under conditions similar to those used to remove grease spots on the porous PE filter prior to installation showed that acetone could have been trapped in the PE filter, corresponding to an initial concentration of 1.5 g acetone/L of water. However, the accumulated amount of organic C taken into account from all these components was insufficient to satisfactorily explain the observed microbially mediated reducing perturbation. Finally, large amounts of dissolved organic C were found to be released in the system by the jelly polymer filling the reference compartment of the pH and E_h electrodes permanently installed over 5 years in flow-through cells on the water circulation loop of the PC experiment. Glycerol was further identified by chromatographic analysis as the main organic compound released by the electrodes. From the analysis results, as well as from the geochemical calculations, the most likely primary organic C source fuelling the microbial perturbation was glycerol released from the polymeric gel filling the reference electrodes (1.6 g glycerol/electrode). Other sources, such as acetone, may also have contributed to microbial processes, but only to a minor extent.     

Copper oxidation state in chalcopyrite: Mixed Cu d and d characteristics

The determination of the oxidation states of copper and iron in sulfides, and chalcopyrite (CuFeS₂) in particular, using 2p X-ray photoemission spectroscopy (XPS) and L_2,3-edge X-ray absorption spectroscopy (XAS) is revisited. Reassessment of the published spectra derived by these methods produces consistent results and reveals the ‘d count’ in the copper compounds to be intermediate between d⁹ and d¹⁰. Nevertheless, these covalent copper compounds can be divided into those nominally monovalent and those nominally divalent. The Fe L_2,3-edge XAS of chalcopyrite, along with Mössbauer data, confirm the presence of high-spin Fe³⁺. Chalcopyrite, despite recent published reports to the contrary, clearly belongs to the monovalent copper class.     

Identification of Archaean plate tectonic processes from multidimensional discrimination diagrams and probability calculations

We applied our group's previously published multidimensional diagrams in 2006–2012 and corresponding probability estimates in 2011–2012 to geochemical data for Archaean rocks compiled from cratons in Australia, South Africa, Brazil, Canada, and India. Tectonic processes similar to present-day plate tectonics evidently were active at least since the Palaeoarchaean (?3570 Ma). This seems to be true in spite of a presumably hotter Earth at that time. For the eastern part of the Pilbara craton (Australia), a Palaeoarchaean (3570–3450 Ma) and Mesoarchaean (2900 Ma) continental arc setting apparently evolved to a collision (Col) setting during the Neoarchaean (2600 Ma). We infer an island arc (IA) environment for Kambalda (Australia) during the Neoarchaean (2700 Ma). For the Barberton belt (South Africa), a transition from a mid-ocean ridge regime during the older part of the Palaeoarchaean (3470 Ma) to an IA setting during the younger part (3300–3260 Ma) is likely. We inferred an arc environment for the São Francisco craton (Brazil) and the Rio Maria terrane (Brazil) during the Mesoarchaean (3085–2983 Ma and 2870 Ma, respectively), whereas a within-plate setting is clearly indicated for the Carajás metallogenic province (Brazil) during the Neoarchaean (2740–2700 Ma). We also recognize an IA regime for the Mesoarchaean (3000 Ma) North Caribou and Neoarchaean (2700 Ma) Abitibi greenstone belts (Canada), and for the Gadwal greenstone belt (India) during the Neoarchaean (2700–2500 Ma). A Col setting was inferred for the Archaean sanukitoid suite (Canada) and the Kolar suture zone (India) during the Neoarchaean (2700–2660 Ma and 2630–2520 Ma, respectively).     

Calculation of multicomponent chemical equilibria and reaction processes in systems involving minerals,gases and an aqueous phase

The compositional characteristics of many geochemical systems which involve the interaction of natural aqueous solutions with minerals and gases are conveniently described using the following thermodynamic components: Cl^?, SO₄⁼, HS^?, CO₃⁼, H⁺, Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺, Fe⁺⁺, Zn⁺⁺, Cu⁺, Al⁺⁺⁺, SiO₂ and H₂O. A set of mass balance and mass action equations equal in number to the number of components plus the number of saturated minerals (and gases) is defined for a specified temperature, pressure and bulk composition. The mass balance equations include terms for minerals, gases and the molalities of aqueous complexes and dissociated species. This set of non-linear equations can be solved with the aid of a computer using'a Newton-Raphson technique. The calculation takes account of aqueous ion complexing, oxidation-reduction equilibria, activity coefficients, non-unit water activity and solid solutions. The use of H⁺, SO₄⁼, HS^? and H₂O as components allows straightforward treatment of processes involving oxidation-reduction, evaporation, boiling and changes of total aqueous H⁺ due to hydrolysis, mineral reaction or temperature change. One product of this approach is a technique for calculating pH at high temperature from measurement of pH at room temperature.By linking a series of discrete overall heterogeneous equilibrium calculations in which incremental changes of bulk composition, temperature or pressure are made, dynamic geochemical processes can be modeled. Example calculations for two such processes are given. These are the heating of seawater from 25° to 300°C and the isothermal irreversible reaction of rhyolite with an aqueous solution at 250°C.     

Biogeochemical processes in a clay formation in situ experiment: Part D - Microbial analyses - Synthesis of results

The purpose of the Porewater Chemistry (PC) experiment at the Mont Terri (MT) Underground Rock Laboratory (URL) was to measure geochemical parameters, such as pH, Eh and pCO₂, in the porewater of the Opalinus Clay formation. Although the PC experiment was designed and implemented carefully from a geochemical perspective, conditions were not sterile and some microbial and nutrient contamination likely occurred. Microbial activity in the added synthetic porewater in the borehole was apparent shortly after initiation of the experiment and affected the geochemical parameters observed in the porewater. This paper summarizes the results from microbial analyses of post-termination PC water and overcore clay samples, conducted to attempt to elucidate the role of microbial activity in the evolution of the geochemical conditions in the PC experiment. Microbial analyses of the PC borehole water, and of clay overcore samples from around the borehole, were carried out at three laboratories and included both molecular biology and culturing methods.Results indicated the presence of heterotrophic aerobic and anaerobic organisms that resulted likely from the initial, non-sterile conditions, sustained by suspected contamination with organic matter (glycerol, acetone). The results also indicated the presence of NO₃-reducers, Fe-reducers, SO₄-reducers and methanogens (i.e., Bacteria as well as Archaea), suggesting a reducing environment with Fe(III)- and SO₄ reduction, and methanogenesis occurring in the PC water and adjacent clay. A black precipitate containing pyrite (identified by XRD and SEM) and a strong H₂S smell in the porewater confirmed the occurrence of SO₄ reduction. Microorganisms identified in the porewater included Pseudomonas stutzeri, Bacillus licheniformis, Desulfosporosinus spp. and Hyphomonas spp. Species identified in enrichment cultures from the overcore samples included Pseudomonas stutzeri, three species of Trichococcus spp., Caldanaerocella colombiensis, Geosporobacter subterrenus and Desulfosporosinus lacus. Overall the results indicated a thriving microbial community in the PC water and adjacent clay in contrast to “undisturbed” Opalinus Clay for which limited evidence for a small viable microbial community has been given in a previous study.     

掺杂Fe、Cd闪锌矿电子结构的第一性原理计算

采用基于密度泛函理论的第一性原理计算方法,对掺Fe和(或)Cd的闪锌矿型Zn S的电子结构进行了计算。计算结果表明,纯闪锌矿的禁带宽度为2.85 e V;掺Fe浓度为3.125%的闪锌矿禁带宽度为2.58 e V,且Fe的3d和S的3p轨道杂化在禁带中引入了两条杂质能级;随着掺Fe量的增加,杂质能级的宽度和峰高也随之增大;掺Cd闪锌矿的禁带宽度为2.68 e V,并在下价带底引入一条杂质能级;Fe/Cd共掺杂的闪锌矿禁带宽度为2.49 e V,在禁带中出现的两条施主杂质能级可提高闪锌矿的可见光响应及催化能力。计算结果为深入探讨天然闪锌矿的可见光催化机制提供了理论支持。