T.M. Seward

Victoria University of Wellington, Wellington, Wellington, New Zealand

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Publications (79)176.63 Total impact

  • Kono H. Lemke, Terry M. Seward
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    ABSTRACT: The M06-2X and B2PLYP-D functionals have been applied to predict structures and energies for (CO2)n clusters up to n = 16. A comparison between M06-2X, B2PLYP-D and benchmark CCSD(T) results indicates that M06-2X is capable of providing accurate binding energies. Stepwise M06-2X (CO2)n clustering free energies exhibit a sharp discontinuity at the magic cluster size n = 13 and systematically shift to more exergonic values with decreasing temperature, in particular for larger clusters. These results indicate that the M06-2X method provides an accurate and cost effective description of non-covalent interactions in (CO2)n clusters and therefore may provide important information on CO2 nucleation phenomena.
    Chemical Physics Letters 06/2013; 573:19–23. · 2.15 Impact Factor
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    ABSTRACT: Adsorbent-trapped volcanic gases, sublimates and condensates from active vents of the La Fossa crater on the island of Vulcano (Aeolian Islands, Italy) as well as ambient and industrial air were quantitatively analyzed by Short-Path Thermal Desorption–Solid Phase Microextraction–Cryotrapping–Gas Chromatography/Mass Spectrometry (SPTD–SPME–CF–GC–MS). Among the over 200 detected and quantified compounds are alkanes, alkenes, arenes, phenols, aldehydes, carboxylic acids, esters, ketones, nitriles, PAHs and their halogenated, methylated and sulfonated derivatives, as well as various heterocyclic compounds including thiophenes and furans. Most compounds are found at concentrations well above laboratory, ambient air, adsorbent and field blank levels. For some analytes (e.g., CFC-11, CH2Cl2, CH3Br), concentrations are up to several orders of magnitude greater than even mid-latitudinal industrial urban air maxima. Air or laboratory contamination is negligible or absent on the basis of noble gas measurements and their isotopic ratios.The organic compounds are interpreted as the product of abiogenic gas-phase radical reactions. On the basis of isomer abundances, n-alkane distributions and substitution patterns the compounds are thought to have formed by high-temperature (e.g., 900 °C) alkyl free radical reactions and halide electrophilic substitution on arenes, alkanes and alkenes. The apparent abiogenic organic chemistry of volcanic gases may give insights into metal transport processes during the formation and alteration of hydrothermal ore deposits, into the natural volcanic source strength of ozone-depleting atmospheric trace gases (i.e., halocarbons), into possibly sensitive trace gas redox pairs as potential early indicators of subsurface changes on volcanoes in the state of imminent unrest, and into the possible hydrothermal origin of early life on Earth, as indicated by the presence of simple amino acids, nitriles, and alkanoic acids.
    Geochimica et Cosmochimica Acta 01/2013; 101:191–221. · 3.88 Impact Factor
  • V. P. Zakaznova-Herzog, T. M. Seward
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    ABSTRACT: The ionization constants of thioarsenous acid have been determined at 22 degrees C by measuring the ultraviolet and visible spectra of thioarsenite species in dilute, aqueous sulfide solutions having S/As = 4.18, As = 1.1 x 10(-4) mol/dm(3) and pH approximate to 6-10.4. No oxidized species such as arsenate, thioarsenate or polysulfides were detected in the experimental solutions. The equilibrium constants for the thioarsenous acid ionization reactions were obtained from a principal component analysis treatment of the spectra and are as follows: H3AsS3 = H+ + H2AsS3- for which pK(a1) = 3.77 (+/- 0.15) H2-AsS32- = H+ + H2AsS3- for which pK(a2) = 6.53 (+/- 0.08) HAsS32- = H+ + AsS33- for which pK(a3) = 9.29 (+/- 0.08) The pK(a)'s for the oxythioarsenous ionization reactions have also been estimated by analogy with those for the end member arsenous and thioarsenous acids. The data emphasize the important role of the simple arsenic(III) thioanions in defining the transport and redox chemistry of arsenic in sulfide-containing natural waters. (C) 2011 Elsevier Ltd. All rights reserved.
    Geochimica et Cosmochimica Acta 01/2012; 83:48-60. · 3.88 Impact Factor
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    ABSTRACT: The concentration of Ti in quartz as an indicator of the temperature conditions of quartz crystallization has gained widespread acceptance since the development of the `TitaniQ' geothermometer of Wark and Watson (2006; Contrib Mineral Petrol 152, 743) and its application in a volcanic context to the Bishop Tuff (Wark et al. 2007; Geology 35, 235). Recent extensions of the TitaniQ model have been made by Thomas et al. (2010; Contrib Mineral Petrol on line, doi:10.1007/s00410-010-0505-3) to incorporate the pressure-dependence of Ti solubility in quartz. Such a geothermobarometer is widespread in application and of interest to workers studying a great variety of crustal rocks. However, there is a significant contrast between the experimental results reported by Thomas et al. (2010) versus conclusions derived from other techniques for the quartz crystals (as well as consistent results from other mineral phases) from silicic volcanic rocks themselves. Here, we draw attention to Ti concentration data from quartz crystals in the 27 ka Oruanui and 760 ka Bishop eruption deposits. In these deposits, other lines of evidence yield pressure estimates for quartz crystal growth at the inferred magmatic temperatures that are between five and ten times less than the lower crustal or upper mantle values derived from the Thomas et al. (2010) formulation. In turn, if pressure estimates for quartz crystallization (from volatile concentrations in gas-saturated melt inclusions) in these examples are taken as accurate then the Thomas et al. (2010) formulation yields temperatures that are demonstrably too low, that is, well below the granite solidus. In either case, the values yielded by the new model are irreconcilable with geological and geophysical observations. Although systematic covariations between Ti concentrations in the experimental quartz crystals and the controlled pressures and temperatures at which they grew have been observed, consideration of the complexities of Ti solubility and speciation in the experimental aqueous fluids suggests that such relationships cannot be simply extrapolated to the natural magmatic environment. The implication is that the theoretical and experimental underpinnings for accurately correlating the Ti contents in magmatic quartz to the temperatures and/or pressures of quartz growth are not soundly based.
    AGU Fall Meeting Abstracts. 12/2010;
  • K. Lemke, S. Sadjadi, T. Seward
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    ABSTRACT: The structures and energetic properties of ionic alkali metal halide clusters play a significant role in our understanding of aqueous geochemical processes such as salt dissolution, precipitation and neutralization reactions. Mass spectrometric and quantum chemical studies of such systems offer new opportunities to study the size-dependent evolution of cluster structures, the occurrence of magic number species as well as their fundamental properties. The work here presents new results for the stability, abundance and structure of pure [Na(NaClm)]+ , [K(KCl)m]+ and mixed [Na(NaCl)p(KCl)q]+ metal halide clusters with m<23 and p+q<14, respectively, using ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS) in combination with the Gn and CBS-x multistep ab initio methods. Ion-cluster experiments were conducted on a modified 7T Bruker FT-ICR/MS equipped with electrospray ionization (ESI) sources and a custom-designed solvent gas inlet interface. In ESI FT-ICR/MS experiments performed with solutions containing NaCl and KCl salts (1mM; 80/20 CH3CN/H2O), singly and doubly charged salt clusters were generated up to a cluster size of [Na(NaCl)22]+, [K(KCl)17]+ and [K2(KCl)21,23]2+, respectively, including “magic number” clusters that correspond to the completed cluster cuboids with the dimensions 3x3x1 (m=4), 3x3x2+3 (m=10) 3x3x3 (m=13) and 3x3x5 (m=22) (see Figure). On the other hand, no pure clusters except [K(KCl)1-3]+ were generated when alkali halides were electrosprayed from 1mM NaCl/KCl solutions. Instead, mixed [Na(NaCl)p(KCl)q]+ clusters are generated up to p+q=14, which are the largest mixed alkali halide clusters yet generated in mass spectrometric experiments, including a suite of ionic species that are generated via CH3CN fragmentation and charge transfer in [Na(CH3CN)n]+ to yield the clusters [Na(NaCN)(CH3CN)n-1]+. We describe our ESI FT-ICR/MS experiments and discuss ion cluster abundances and extent of clustering in terms of variation of the solvent, desolvation temperature, ESI capillary and cone voltage as well as solution concentration. We also report and compare local minima geometries and relative energies for a number of representative [Na(NaCl)m]+ and [K(KCl)m]+ clusters using the composite CBS-QB3 and G4 methods and comment on the onset of the doubly charged cluster series. FT-ICR mass spectra for [Na(NaCl)n]+ clusters generated from 1mM NaCl in 20%H2O 80% acetonitrile in positive ion mode.
    AGU Fall Meeting Abstracts. 12/2010;
  • Z. Minubayeva, T.M. Seward
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    ABSTRACT: This UV spectrophotometric study was aimed at providing precise, experimentally derived thermodynamic data for the ionisation of molybdic acid (H2MoO4) from 30 to 300 °C and at equilibrium saturated vapour pressures. The determination of the equilibrium constants and associated thermodynamic parameters were facilitated by spectrophotometric measurements using a specially designed high temperature optical Ti–Pd flow-through cell with silica glass windows.The following van’t Hoff isochore equations describe the temperature dependence of the first and second ionisation constants of molybdic acid up to 300 °C: The resulting ionisation constants of molybdic acid demonstrate that in low sulphur containing hydrothermal fluids in the Earth’s crust, the transport of molybdenum is favoured by the species while the role of the associated H2MoO4 is of negligible importance at elevated temperatures above 200 °C.
    Geochimica et Cosmochimica Acta 01/2010; 74(15):4365-4374. · 3.88 Impact Factor
  • B. R. Tagirov, T. M. Seward
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    ABSTRACT: The solubility of synthetic ZnS(cr) was measured at 25–250°C and P=150bars as a function of pH in aqueous sulfide solutions (~0.015–0.15m of total reduced sulfur). The solubility determinations were performed using a Ti flow-through hydrothermal reactor. The solubility of ZnS(cr) was found to increase slowly with temperature over the whole pH range from 2 to ~10. The values of the Zn–S–HS complex stability constant, β, were determined for Zn(HS)20(aq), Zn(HS)3−, Zn(HS)42−, and ZnS(HS)−. Based on the experimental values the Ryzhenko–Bryzgalin electrostatic model parameters for these stability constants were calculated, and the ZnS(cr) solubility and the speciation of Zn in sulfide-containing hydrothermal solutions were evaluated. The most pronounced solubility increase, about 3 log units at m(Stotal)=0.1 for the temperatures from 25 to 250°C, was found in acidic solutions (pH~3 to 4) in the Zn(HS)20(aq) predominance field. In weakly alkaline solutions, where Zn(HS)3− and Zn(HS)42− are the dominant Zn–S–HS complexes, the ZnS(cr) solubility increases by 1 log unit at the same conditions. It was found that ZnS(HS)− and especially Zn(HS)42− become less important in high temperature solutions. At 25°C and m(Stotal)=0.1, these species dominate Zn speciation at pH>7. At 100°C and m(Stotal)=0.1, the maximum fraction of Zn(HS)42− is only 20% of the total Zn concentration (i.e. at pHt~7.5), whereas at 350°C and 3
    Chemical Geology - CHEM GEOL. 01/2010; 269(3):301-311.
  • Kono H. Lemke, S. K. Butt, Terry M. Seward
    Geochmica et Cosmochimica Acta 06/2009;
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    K. H. Lemke, T. M. Seward
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    ABSTRACT: We present results from ab initio calculations for the structures, energetics and atmospheric abundances of neutral clusters containing water, carbon dioxide and nitrous oxide up to 45km altitude using the complete basis set CBS-Q and G3 multi-level procedures. Gas phase hydration energies, enthalpies and entropies for the stepwise attachment of water onto clusters according to X(H2O)n + H2O = X(H2O)n+1 (where X = H2O, CO2 and N2O) are reported for up to n=5. In particular, our results demonstrate that values for the incremental hydration enthalpies and entropies of all three gases H2O, CO2 and N2O asymptotically approach values characteristic of bulk liquid water (i.e. -44.0 kJ/mol for the enthalpy and -118.8 J/Kmol for the entropy of condensation) following attachment of around 3-4 water molecules. Interestingly, our calculated number densities for the water dimer at 292Kelvin are in excellent agreement with recent values obtained from IR measurements of atmospheric media (Pfeilsticker et al., 2003, Science). Our quantum chemical calculations indicate that water attachment onto H2O, CO2 and N2O is a thermodynamically favorable process, such that hydrated clusters would form a significant atmospheric repository of these species.
    Journal of Geophysical Research 10/2008; 113(D19). · 3.17 Impact Factor
  • Kono H. Lemke, Terry M. Seward
    Geochmica et Cosmochimica Acta 07/2008; 72(12).
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    ABSTRACT: The temperature and pressure dependences of pK for acridine ion ionization were determined up to 200 °C and 2000 bar. The UV-Vis measurements at high temperatures and pressures were conducted in flow-through spectrophotometric cells. Two independent series of experiment were performed: one in a Ti–Pd cell with silica quartz windows for measurements in the ultraviolet region, and another in a Ti grade 5 cell with sapphire windows for use at higher pressures, which permitted measurements in the visible region. Combined chemometric and thermodynamic analyses of the UV-Vis spectrophotometric data were used to extract the ionization constants as well as the changes in molar volume ΔV° for acridine protonation as functions of temperature and pressure. Values of pK decrease from 5.52 to 3.74 with increasing temperature from 25 to 200 °C at saturated water-vapor pressure. The pressure dependence of acridinium ion ionization is small (e.g., pK=5.5 at 25 °C and 2000 bar) and is characterized by positive ΔV°≤1.2cm3⋅mol−1, which is not surprising for this type of isocoulombic reaction involving a large molecule.
    Journal of Solution Chemistry 01/2008; 37(3):291-305. · 1.13 Impact Factor
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    Kono H. Lemke, Terry M. Seward
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    ABSTRACT: Reports of the high ion content of steam and low-density supercritical fluids date back to the work of Carlon [Carlon H. R. (1980) Ion content of air humidified by boiling water.J. Appl.Phys.51, 171–173], who invoked ion and neutral-water clustering as mechanism to explain why ions partition into the low-density aqueous phase. Mass spectrometric, vibrational spectroscopic measurements and quantum chemical calculations have refined this concept by proposing strongly bound ion–solvent aggregates and water clusters such as Eigen- and Zundel-type proton clusters H3O+·(H2O)m and the more weakly bound water oligomers (H2O)m. The extent to which these clusters affect fluid chemistry is determined by their abundance, however, little is known regarding the stability of such moieties in natural low-density high-temperature fluids. Here we report results from quantum chemical calculations using chemical-accuracy multi-level G3 (Curtiss–Pople) and CBS-Q theory (Peterson) to address this question. In particular, we have investigated the cluster structures and clustering equilibria for the ions and H3S+·(H2O)m(H2S)n, where m ⩽ 6 and n ⩽ 4, at 300–1000 K and 1 bar as well as under vapor–liquid equilibrium conditions between 300 and 646 K. We find that incremental hydration enthalpies and entropies derived from van’t Hoff analyses for the attachment of H2O and H2S onto H3O+, and H3S+ are in excellent agreement with experimental values and that the addition of water to all three ions is energetically more favorable than solvation by H2S. As clusters grow in size, the energetic trends of cluster hydration begin to reflect those for bulk H2O liquids, i.e. calculated hydration enthalpies and entropies approach values characteristic of the condensation of bulk water (ΔHo = −44.0 kJ mol−1, ΔSo = −118.8 J K mol−1). Water and hydrogen sulfide cluster calculations at higher temperatures indicate that a significant fraction of H3O+, and H3S+ ions exists as solvated moieties.
    Geochimica et Cosmochimica Acta 01/2008; · 3.88 Impact Factor
  • Andri Stefánsson, Terry M. Seward
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    ABSTRACT: The hydrolysis of iron(III) was studied in acid aqueous solutions between 25 and 200 °C at saturated water vapour pressure by uv–vis spectrophotometry using a high-temperature, flow-through gold-lined optical cell. The strong ligand-to-metal charge transitions of iron(III) hydroxo complexes at wavelengths below 400 nm were used to obtain molar absorptivities, ε, and equilibrium hydrolysis constants using principal component analysis of the spectra. The total iron(III) concentrations ranged from 6.184 × 10− 5 to 1.652 × 10− 4 mol kg− 1 and the perchloric acid concentration was between 9.31 × 10− 4 and 0.398 mol kg− 1. Under these conditions two iron(III) species were identified, Fe3+ and FeOH2+, and the corresponding hydrolysis constant according to the reactionFe3+ + H2O = FeOH2+ + H+increased from logβ1 = − 2.18 ± 0.01 at 25 °C to 0.54 ± 0.15 at 200 °C. The hydrolysis of Fe3+ to form FeOH2+ is predominantly driven by positive entropy indicating electrostatic interaction between Fe3+ and OH−.
    Chemical Geology. 01/2008; 249:227-235.
  • O. M. Suleimenov, T. M. Seward, J. K. Hovey
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    ABSTRACT: The formation constant of the mononitratouranyl complex was studied spectrophotometrically at temperatures of 25, 40, 55, 70, 100 and 150 °C (298, 313, 328, 343, 373 and 423 K). The uranyl ion concentration was fixed at approximately 0.008 mol⋅kg−1 and the ligand concentration was varied from 0.05 to 3.14 mol⋅kg−1. The uranyl nitrate complex, UO2NO3+, is weak at 298 K but its equilibrium constant (at zero ionic strength) increases with temperature from log 10 β 1=−0.19±0.02 (298 K) to 0.78±0.04 (423 K).
    Journal of Solution Chemistry 08/2007; 36(9):1093-1102. · 1.13 Impact Factor
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    ABSTRACT: 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.
    Geochimica et Cosmochimica Acta 05/2007; · 3.88 Impact Factor
  • Jenny S. Cox, Terry M. Seward
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    ABSTRACT: Experimental data on the hydrothermal reaction kinetics of aspartic acid were acquired using a custom-built spectrophotometric reaction cell which permits in situ observation under hydrothermal conditions. The results of this study indicate that the reaction kinetics of dilute aspartic acid solutions are significantly different depending on the presence or absence of catalytic surfaces such as standard metal alloys. The spectroscopic data presented here represent the first direct observations, in situ and in real time, of an amino acid reacting in a hydrothermal solution. Quantitative kinetic information, including rate constants, concentration versus time profiles, and calculations of the individual component spectra, was obtained from the data using a chemometric approach based on factor analysis/principle component analysis which treats the rate expressions simultaneously as a system of differential algebraic equations (DAE) of index 1. Identification of the products was confirmed where possible by high pressure anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The reaction kinetics of aspartic acid under hydrothermal conditions was observed to be highly complex, in contrast to previous studies which indicated almost exclusively deamination. At lower temperatures (120–170 °C), several different reaction pathways were observed, including decarboxylation and polymerization, and the catalytic effects of reactor surfaces on the aspartic acid system were clearly demonstrated. At higher temperatures (above 170 °C), aspartic acid exhibited highly complex behaviour, with evidence indicating that it can simultaneously dimerize and cyclize, deaminate (by up to two pathways), and decarboxylate (by up to two pathways). These higher temperature kinetics were not fully resolvable in a quantitative manner due to the complexity of the system and the constraints of UV spectroscopy. The results of this study provide strong evidence that the reaction kinetics of aspartic acid are very sensitive to parameters such as temperature, reactor materials (i.e., reactive surfaces), and additives, and that previous observations on aspartic acid were specific to the choice of experimental conditions.
    Geochimica et Cosmochimica Acta 01/2007; · 3.88 Impact Factor
  • Jenny S. Cox, Terry M. Seward
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    ABSTRACT: Experimental data on the hydrothermal reaction kinetics of α-alanine, glycine, and β-alanine were acquired using a custom-built spectrophotometric reaction cell which permits in situ observation under hydrothermal conditions. Quantitative kinetic information, including rate constants, concentration versus time profiles, and calculations of the individual component spectra, was obtained from the data using a self-modeling chemometric approach based on factor analysis which treats the rate expressions simultaneously as a system of differential algebraic equations (DAE) of index 1. Experimental data collected at 120–165 °C and 20 bar indicates that aqueous α-alanine, glycine and β-alanine will preferentially undergo dimerization and subsequent cyclization when heated in an inert reactor. The results presented here lend further support to the roles of temperature, exposed reactive surfaces, and matrix additives in the reaction kinetics of the structurally simple amino acids examined in this study.
    Geochimica et Cosmochimica Acta 01/2007; · 3.88 Impact Factor
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    ABSTRACT: The soluble and insoluble hydrolysis products of palladium were investigated in aqueous solutions of 0.6 mol kg−1 NaCl at 298.2 K. Potentiometric titrations of millimolal palladium(II) solutions were used to monitor hydrolysis reactions of the mononuclear PdCl3OH2− and species. Spectrophotometric titrations were also used to corroborate the speciation change and to extract the correlative molar absorption coefficients for the PdCl3OH2− species in the 210–320 nm range. Longer-term potentiometric titrations systematically yielded precipitates which matured over a period of 6 weeks and resulted in a more extensive release of protons to the solution. Precipitation experiments in the 3–11 pH range showed the dominant precipitating phase to be Pd(OH)1.72Cl0.28. EXAFS measurements yielded an average of 3.50 O and 0.50 Cl atoms per Pd atom with a Pd–O distance of 2.012 Å and a Pd–Cl distance of 2.185 Å. Speciation modeling of proton and palladium mass balance data of experiments for palladium concentrations ranging from 0.047 to 10.0 mmol kg−1 required the presence of polynuclear complexes containing 3–9 palladium atoms. The existence of such complexes is moreover supported by previous investigations of palladium hydroxide chains of the type [Pd(OH)1.72Cl0.28]n, that are coiled and/or aggregated into nanometer-sized (15–40 Å) spheroids.
    Geochimica et Cosmochimica Acta 01/2007; 71(20):4834-4845. · 3.88 Impact Factor
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    ABSTRACT: The solubility of ZnS(cr) was measured at 100 °C, 150 bars in sulfide solutions as a function of sulfur concentration (m(Stotal) = 0.02–0.15) and acidity (pHt = 2–11). The experiments were conducted using a Ti flow-through hydrothermal reactor enabling the sampling of large volumes of solutions at experimental conditions, with the subsequent concentration and determination of trace quantities of Zn. Prior to the experiments, a long-term in situ conditioning of the solid phase was performed in order to attain the reproducible Zn concentrations (i.e. solubilities). The ZnS(cr) solubility product was monitored in the course of the experiment. The following species were found to account for Zn speciation in solution: Zn2+ (pHt < 3), (pHt 3–4.5), (pHt 5–8), and ZnS(HS)− (pHt > 8) (pHt predominance regions are given for m(Stotal) = 0.1). Solubility data collected in this study at pHt > 3 were combined with the ZnS(cr) solubility product determined at lower pH to yield the following equilibrium constants (t = 100 °C, P = 150 bars):The solubilities of ZnS(cr), determined beyond the Zn2+ predominance region (at pHt > 2.5), are lower than the sphalerite solubilities previously reported in the literature, resulting in lower values of the formation constants for the Zn–S–HS complexes. The results of this study indicate that in natural sulfide-rich fluids the maximum Zn concentrations are attained at pH = pK1(H2S), where predominates.
    Geochimica et Cosmochimica Acta 01/2007; 71(20):4942-4953. · 3.88 Impact Factor
  • K. Lemke, T. Seward
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    ABSTRACT: The structures and thermochemical properties of hydrated ions and neutral molecules play an important role in our understanding of solvent clustering and hydrogen bonding in the gas phase. Considerable effort therefore has been devoted to both the experimental and theoretical determination of stepwise hydration energies of geochemically important ions and neutral molecules with solvents, for instance H2O or H2S, over a broad range of temperatures typical of those encountered in volcanic gases. Because volcanic gases contain mutiple solute and solvent components which are subject to proton transfer, competive solvation and solvent switching, characterizing individual clusters has been a fundamental challenge to a molecular-level understanding of high temperature gas-phase solvation. However, recent advances in computational chemistry methods, especially Pople´s Gaussian (G-n) and complete basis set limit (CBS-x) model chemistries, now allow characterization of the dominant cluster structures and thermochemical properties of solute-solvent and solvent-solvent interactions in high temperature volcanic gases. Building on reported measurements of volcanic gases at Vesuvio, Italy, and Showa-Shinzan, Japan, as well as our recent investigations of ion-hydration we have re-examined the high temperature clustering equilibria of the small hydronium (H3O+) and ammonium (NH4+) ions as well as neutral ammonia and sulphur species with H2O and/or H2S using ab initio quantum chemical methods. From our study, we find that most of the gas phase ions tend to associate with a small number of H2O and H2S molecules to yield a hydrated ion cluster even at low humidities. Furthermore, inspection of van´t Hoff data demonstrate that (1) hydration energies of ions are shifted to less exergonic values as the solvent shell grows and the composition shifts from water-rich to hydrogen sulphide rich, (2) ion-cluster size increases with decreasing temperature at constant humidity, (3) attachment of H2S onto neutral ammonia is substantially more endergonic than the corresponding reaction with H2O and (4) temperature increases are reflected in a weakening of the hydrogen bonding in neutral ammonia clusters. For instance, we predict that the concentrations of NH3(H2O) clusters in fumarolic gases (H2O=740Torr) of the Showa- Shinzan volcano are 5.8x1014cm-3 at 371K but are reduced to 2.7x1013cm-3at 743K. In general, the observed energetic trends demonstrate the significance of hydrogen-bonded networks in both ionic and neutral solvent clusters at elevated temperatures.
    AGU Fall Meeting Abstracts. 11/2006; -1:1733.

Publication Stats

653 Citations
176.63 Total Impact Points

Institutions

  • 2010–2013
    • Victoria University of Wellington
      • School of Geography, Environment and Earth Sciences
      Wellington, Wellington, New Zealand
  • 1997–2008
    • ETH Zurich
      • Institute of Geochemistry and Petrology
      Zürich, ZH, Switzerland
  • 2003
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland
  • 1999–2000
    • The University of Manchester
      Manchester, England, United Kingdom
  • 1996
    • Pennsylvania State University
      • Department of Geosciences
      University Park, Maryland, United States
    • Hochschule für Technik Zürich
      Zürich, Zurich, Switzerland