Aqueous Liquid Vapor Research Articles

Impact of Tetrabutylammonium on the Oxidation of Bromide by Ozone.

The reaction of ozone with sea-salt derived bromide is relevant for marine boundary layer atmospheric chemistry. The oxidation of bromide by ozone is enhanced at aqueous interfaces. Ocean surface water and sea spray aerosol are enriched in organic compounds, which may also have a significant effect on this reaction at the interface. Here, we assess the surface propensity of cationic tetrabutylammonium at the aqueous liquid–vapor interface by liquid microjet X-ray photoelectron spectroscopy (XPS) and the effect of this surfactant on ozone uptake to aqueous bromide solutions. The results clearly indicate that the positively charged nitrogen group in tetrabutylammonium (TBA), along with its surface activity, leads to an enhanced interfacial concentration of both bromide and the bromide ozonide reaction intermediate. In parallel, off-line kinetic experiments for the same system demonstrate a strongly enhanced ozone loss rate in the presence of TBA, which is attributed to an enhanced surface reaction rate. We used liquid jet XPS to obtain detailed chemical composition information from the aqueous-solution–vapor interface of mixed aqueous solutions containing bromide or bromide and chloride with and without TBA surfactant. Core level spectra of Br 3d, C 1s, Cl 2p, N 1s, and O 1s were used for this comparison. A model was developed to account for the attenuation of photoelectrons by the carbon-rich layer established by the TBA surfactant. We observed that the interfacial density of bromide is increased by an order of magnitude in solutions with TBA. The salting-out of TBA in the presence of 0.55 M sodium chloride is apparent. The increased interfacial bromide density can be rationalized by the association constants for bromide and chloride to form ion-pairs with TBA. Still, the interfacial reactivity is not increasing simply proportionally with the increasing interfacial bromide concentration in response to the presence of TBA. The steady state concentration of the bromide ozonide intermediate increases by a smaller degree, and the lifetime of the intermediate is 1 order of magnitude longer in the presence of TBA. Thus, the influence of cationic surfactants on the reactivity of bromide depends on the details of the complex environment at the interface.

Temperature effects on the spatial distribution of electrolyte mixtures at the aqueous liquid-vapor interface.

The microscopic picture of ions at the aqueous liquid-vapor interface continues to be an important and active area of research. Both experiments and simulations have shown that certain ions, such as Br- and I-, prefer to adsorb at the interface, but there is not yet a consensus as to the relative importance of various ion-specific properties that influence surface solvation. In a previous study, we systematically explored the effect of ion size on determining whether or not a monovalent ion would adsorb at the surface, and found that, for electrolyte mixtures represented by non-polarizable models, the larger/smaller anions are enriched/depleted at the interface. Here, we extend that study to include temperature effects enabling a van't Hoff analysis of the enthalpic and entropic contributions. We perform configurational-bias Monte Carlo simulations in the Gibbs ensemble to investigate the partitioning of mixtures of differently sized ions at the aqueous liquid-vapor interface from 284.09 K to 347.22 K at a pressure of 1 atm. Ions are represented using our own previously developed models that vary only in size (i.e., the Lennard-Jones σ parameter changes, while all other parameters are held constant across ion types). System properties studied include surface tension, interfacial width, ion surface excess, number density profiles, z-dependent transfer free energy, enthalpy, entropy, and anion-cation coordination numbers.

Microthermometric behavior of crystal-rich inclusions in spodumene under confining pressure

Abstract A hydrothermal diamond anvil cell (HDAC) was used to observe the microthermometric behavior of solid + liquid + vapor inclusions in spodumene from the Tanco pegmatite, Manitoba, under confining pressure. At 25 °C, these inclusions commonly contain a carbonate mineral (zabuyelite, rarely calcite or nahcolite), quartz, a phyllosilicate (cookeite), and an aqueous carbonic fluid phase. Heating spodumene-hosted inclusions to temperatures between 600 and 680 °C in a HDAC resulted in total or partial dissolution of the contained solid phases, followed by homoepitaxial growth of new spodumene on the inclusion walls, which reduced the inclusion volume by up to 31%. At room temperature, the homogenized inclusions contain only an aqueous fluid phase, CO2 liquid, and CO2 vapor. Inclusions that failed to homogenize at 680 °C, or leaked during heating, contain partially dissolved minerals with or without an aqueous carbonic fluid. The volume of spodumene formed within an inclusion during experimental re-heating, as determined by the difference in inclusion size before and after total dissolution of the contained solid phases, was used to estimate the volume of zabuyelite, quartz/cristobalite, and cookeite produced by the reaction The relative volumes of the calculated reaction products approximate the proportions of zabuyelite, quartz/cristobalite, and cookeite in inclusions prior to heating. The absence of silicate glass in the quenched homogenized inclusions indicates that they do not represent the crystallized products of an entrapped hydrous silicate melt that wetted the surface of spodumene during its growth. Large changes in inclusion volume and composition during experimental re-heating shows that the inclusions are neither isochoric nor isoplethic systems and as such are unsuitable for estimating the P-T conditions of trapping. Readers should therefore exercise caution when using thermobaric estimates of pegmatite crystallization inferred from microthermometric measurements of presumably primary melt inclusions in spodumene.

Aqueous Nanoclusters Govern Ion Partitioning in Dense Polymer Membranes.

The uptake and sorption of charged molecules by responsive polymer membranes and hydrogels in aqueous solutions is of key importance for the development of soft functional materials. Here, we investigate the partitioning of simple monatomic (Na+, K+, Cs+, Cl–, I–) and one molecular ion (4-nitrophenolate; NP–) within a dense, electroneutral poly(N-isopropylacrylamide) membrane using explicit-water molecular dynamics simulations. Inside the predominantly hydrophobic environment, water distributes in a network of polydisperse water nanoclusters. The average cluster size determines the mean electrostatic self-energy of the simple ions, which preferably reside deeply inside them; we therefore find substantially larger partition ratios K ≃10–1 than expected from a simple Born picture using a uniform dielectric constant. Despite their irregular shapes, we observe that the water clusters possess a universal negative electrostatic potential with respect to their surroundings, as is known for aqueous liquid–vapor interfaces. This potential, which we find concealed in cases of symmetric monatomic salts, can dramatically impact the transfer free energies of larger charged molecules because of their weak hydration and increased affinity to interfaces. Consequently, and in stark contrast to the simple ions, the molecular ion NP– can have a partition ratio much larger than unity, K ≃10–30 (depending on the cation type) or even 103 in excess of monovalent salt, which explains recent observations of enhanced reaction kinetics of NP– reduction catalyzed within dense polymer networks. These results also suggest that ionizing a molecule can even enhance the partitioning in a collapsed, rather hydrophobic gel, which strongly challenges the traditional simplistic reasoning.

The physical and chemical evolution of fluids in rare-element granitic pegmatites associated with the Lacorne pluton, Québec, Canada

Co-magmatic rare-element (Be, Li, Nb, Ta) granitic pegmatites associated with the Lacorne monzogranite pluton of the Preissac-Lacorne batholith (Québec) range from a least evolved beryl-type in the pluton through a transitional beryl + spodumene-type to a most evolved spodumene-type in mafic country rocks. They possess internal lithologic fabrics and primary fluid inclusions that provide evidence for saturation of the magma with aqueous fluids immediately after the formation of aplite in the beryl pegmatite, and pene-contemporaneously with formation of the beryl + spodumene and spodumene pegmatites. The early fluids are represented by aqueous liquid-vapor (Type 1a) and aqueous liquid-vapor-solid (Type 2) inclusions in beryl from beryl and beryl + spodumene pegmatites and are estimated to have been trapped between 500 and 550 °C and at 3.5 Kb. On the basis of microthermometric measurements, analyses of the compositions of the precipitates from decrepitated inclusions and the nature of the solids (trapped), these fluids are interpreted to have been NaCl-dominated (≤16 wt% NaCl eq.) and to have contained appreciable Fe and dissolved CO2. In spodumene pegmatite, the equivalent fluid, which was trapped at 450 to 500 °C, contained significant Mn, Li and Cs in place of Fe, consistent with corresponding trends in the chemical evolution of the host rock.Volatile-rich, mainly secondary, aqueous fluid inclusions (Type 1b) trapped in beryl are interpreted to reflect temporary sharp drops in pressure later in the crystallization history of the beryl-bearing pegmatites due to local fluid overpressures that led to brecciation and consequent pressure release. These inclusions have high salinity, are CaCl2-rich and are considered to represent magmatic hydrothermal fluids that acquired their calcium as a result of their interaction with the host Lacorne pluton. Incursion of CaCl2-rich fluids into the spodumene pegmatites is interpreted to have occurred earlier in their crystallization history, i.e., upon emplacement of the pegmatites, as shown by the fact that a high proportion of primary inclusions in spodumene in these pegmatites contains considerable calcium, and calcium contents are generally higher in inclusions in spodumene than in beryl. The inclusions in the spodumene pegmatites are thought to have acquired their calcium through interaction of the fluids with the amphibolites (metabasalts) that host these intrusions.The crystallization of the pegmatites terminated with the entrapment of low-salinity aqueous‑carbonic fluids (Type 3 inclusions) in quartz (6–10 wt% NaCl eq.), which most likely formed as a result of the unmixing of the magmatic fluid into separate aqueous and carbonic fluids, probably at temperatures between 250 and 350 °C.The results of this study show that aqueous fluid saturation can take place at an early stage of pegmatite emplacement, and that magma evolution is matched by changes in the solute chemistry of the exsolving aqueous fluid. They also show that evolution to a more volatile-rich composition (H2O + F + Li) may have contributed to the increased mobility of later magma batches, thereby helping to explain the regional zonation of the pegmatites, from beryl-type within the pluton to spodumene-type in the adjacent amphibolite.

Genesis of the Huangshaping W–Mo–Cu–Pb–Zn polymetallic deposit in Southeastern Hunan Province, China: Constraints from fluid inclusions, trace elements, and isotopes

The Huangshaping polymetallic deposit is located in southeastern Hunan Province, China. It is a world-class W–Mo–Pb–Zn–Cu skarn deposit in the Nanling Range Metallogenic Belt, with estimated reserves of 74.31Mt of W–Mo ore at 0.28% WO3 and 0.07% Mo, 22.43Mt of Pb–Zn ore at 3.6% Pb and 8.00% Zn, and 20.35Mt of Cu ore at 1.12% Cu. The ore district is predominantly underlained by carbonate formations of the Lower Carboniferous period, with stocks of quartz porphyry, granite porphyry, and granophyre. Skarns occurred in contact zones between stocks and their carbonate wall rocks, which are spatially associated with the above-mentioned three types of ores (i.e., W–Mo, Pb–Zn, and Cu ores).Three types of fluid inclusions have been identified in the ores of the Huangshaping deposit: aqueous liquid–vapor inclusions (Type I), daughter-mineral-bearing aqueous inclusions (Type II), and H2O–CO2 inclusions (Type III). Systematic microthermometrical, laser Raman spectroscopic, and salinity analyses indicate that high-temperature and high-salinity immiscible magmatic fluid is responsible for the W–Mo mineralization, whereas low-temperature and low-salinity magmatic-meteoric mixed fluid is responsible for the subsequent Pb–Zn mineralization. Another magmatic fluid derived from deep-rooted magma is responsible for Cu mineralization.Chondrite-normalized rare earth element patterns and trace element features of calcites from W–Mo, Pb–Zn, and Cu ores are different from one another. Calcite from Cu ores is rich in heavy rare earth elements (187.4–190.5ppm), Na (0.17%–0.19%), Bi (1.96–64.60ppm), Y (113–135ppm), and As (9.1–29.7ppm), whereas calcite from W–Mo and Pb–Zn ores is rich in Mn (>10.000ppm) and Sr (178–248ppm) with higher Sr/Y ratios (53.94–72.94). δ18O values also differ between W–Mo/Pb–Zn ores (δ18O=8.10‰–8.41‰) and Cu ores (δ18O=4.34‰–4.96‰), indicating that two sources of fluids were, respectively, involved in the W–Mo, Pb–Zn, and Cu mineralization.Sulfur isotopes from sulfides also reveal that the large variation (4‰–19‰) within the Huangshaping deposit is likely due to a magmatic sulfur source with a contribution of reduced sulfate sulfur host in the Carboniferous limestone/dolomite and more magmatic sulfur involved in the Cu mineralization than that in W–Mo and Pb–Zn mineralization. The lead isotopic data for sulfide (galena: 206Pb/204Pb=18.48–19.19, 207/204Pb=15.45–15.91, 208/204Pb=38.95–39.78; sphalerite: 206Pb/204Pb=18.54–19.03, 207/204Pb=15.60–16.28, 208/204Pb=38.62–40.27; molybdenite: 206Pb/204Pb=18.45–19.21, 207/204Pb=15.53–15.95, 208/204Pb=38.77–39.58 chalcopyrite: 206Pb/204Pb=18.67–19.38, 207/204Pb=15.76–19.90, and 208/204Pb=39.13–39.56) and oxide (scheelite: 206Pb/204Pb=18.57–19.46, 207/204Pb=15.71–15.77, 208/204Pb=38.95–39.13) are different from those of the wall rock limestone (206Pb/204Pb=18.34–18.60, 207/204Pb=15.49–15.69, 208/204Pb=38.57–38.88) and porphyries (206Pb/204Pb=17.88–18.66, 207/204Pb=15.59–15.69, 208/204Pb=38.22–38.83), suggesting Pb206-, U238-, and Th 232-rich material are involved in the mineralization. The Sm–Nd isotopes of scheelite (εNd(t)=−6.1 to −2.9), garnet (εNd(t)=−6.8 to −6.1), and calcite (εNd(t)=−6.3) from W–Mo ores as well as calcite (εNd(t)=−5.4 to −5.3) and scheelite (εNd(t)=−2.9) from the Cu ores demonstrate suggest more mantle-derived materials involved in the Cu mineralization.In the present study we conclude that two sources of ore-forming fluids were involved in production of the Huangshaping W–Mo–Pb–Zn–Cu deposit. One is associated with the granite porphyry magmas responsible for the W–Mo and then Pb–Zn mineralization during which its fluid evolved from magmatic immiscible to a magmatic–meteoritic mixing, and the other is derived from deep-rooted magma, which is related to Cu-related mineralization.

Geochemical and geochronological constraints on the formation of shear-zone hosted Cu–Au–Bi–Te mineralization in the Stanos area, Chalkidiki, northern Greece

Copper–gold–bismuth–tellurium mineralization in the Stanos area, Chalkidiki Peninsula, Greece, occurs in the Proterozoic- to Silurian-aged Serbomacedonian Massif, which tectonically borders the Mesozoic Circum-Rhodope metamorphic belt to the west and crystalline rocks of the Rhodope Massif to the east. This area contains the Paliomylos, Chalkoma, and Karambogia prospects, which are spatially related to regional NW–SE trending shear zones and hosted by marble, amphibolite gneiss, metagabbro, and various muscovite–biotite–chlorite–actinolite–feldspar–quartz schists of the Silurian Vertiskos Unit. Metallic minerals occur as disseminated to massive aggregates along foliation planes and in boudinaged quartz veins. Iron-bearing sulfides (pyrite, arsenopyrite, and pyrrhotite) formed prior to a copper-bearing stage that contains chalcopyrite along with galena, sphalerite, molybdenite, and various minerals in the system Bi–Cu–Pb–Au–Ag–Te. Fluid inclusion homogenization temperatures of primary aqueous liquid–vapor inclusions in stage I quartz veins range from 170.1°C to 349.6°C (peak at ~230°C), with salinities of 4.5 to 13.1wt.% NaCl equiv. Calculated isochores intersect P–T conditions associated with the upper greenschist facies caused by local overpressures during late-stage tectonic movement along the shear zone in the Eocene, which produced stretching and unroofing of rocks in the region. Values of δ34S for sulfides in the Stanos shear zone range from 2.42 to 10.19‰ and suggest a magmatic sulfur source with a partially reduced seawater contribution. For fluids in equilibrium with quartz, δ18O at 480°C varies from 5.76 to 9.21‰ but does not allow for a distinction between a metamorphic and a magmatic fluid.A 187Re–187Os isochron of 19.2±2.1Ma for pyrite in the Paliomylos prospect overlaps ages obtained previously from intrusive rocks spatially-related to the Skouries porphyry Cu–Au, the Asimotrypes Au, and the intrusion-related Palea Kavala Bi–Te–Pb–Sb±Au deposits in northern Greece, as well as alteration minerals in the carbonate-replacement Madem Lakkos Pb–Zn deposit. Ore-forming components of deposits in the Stanos area were likely derived from magmatic rocks at shallow depth that intruded an extensional shear environment at ~19Ma.

Association of alkanes with the aqueous liquid-vapor interface: a reference system for interpreting hydrophobicity generally through interfacial fluctuations.

We report free energy calculations and fluctuation profiles of single alkanes (from methane to pentane) along the direction normal to the air-water interface. The induced fluctuations and the interfacial stabilities of alkanes are found to be correlated and similar to the results of inorganic monovalent ions (Ou et al., J. Phys. Chem. B, 2013, 117, 11732). This suggests that hydrophobic solvation of solutes and ions is important in determining the adsorption behavior.

Ion-specific induced fluctuations and free energetics of aqueous protein hydrophobic interfaces: toward connecting to specific-ion behaviors at aqueous liquid-vapor interfaces.

We explore anion-induced interface fluctuations near protein–water interfaces using coarse-grained representations of interfaces as proposed by Willard and Chandler (J. Phys. Chem. B2010, 114, 1954−195820055377). We use umbrella sampling molecular dynamics to compute potentials of mean force along a reaction coordinate bridging the state where the anion is fully solvated and one where it is biased via harmonic restraints to remain at the protein–water interface. Specifically, we focus on fluctuations of an interface between water and a hydrophobic region of hydrophobin-II (HFBII), a 71 amino acid residue protein expressed by filamentous fungi and known for its ability to form hydrophobically mediated self-assemblies at interfaces such as a water/air interface. We consider the anions chloride and iodide that have been shown previously by simulations as displaying specific-ion behaviors at aqueous liquid–vapor interfaces. We find that as in the case of a pure liquid–vapor interface, at the hydrophobic protein–water interface, the larger, less charge-dense iodide anion displays a marginal interfacial stability compared with that of the smaller, more charge-dense chloride anion. Furthermore, consistent with the results at aqueous liquid–vapor interfaces, we find that iodide induces larger fluctuations of the protein–water interface than chloride.

Clathrate Hydrate Equilibrium Data for the Gas Mixture of Carbon Dioxide and Nitrogen in the Presence of an Emulsion of Cyclopentane in Water

Carbon dioxide and nitrogen gas separation is achieved through clathrate hydrate formation in the presence of cyclopentane. A phase diagram is presented in which the mole fraction of CO2 in the gas phase is plotted against the mole fraction of CO2 in the carbon dioxide + nitrogen + cyclopentane mixed hydrate phase, both defined with respect to total amount of CO2 and N2 in the respective phase. The curve is plotted for temperatures ranging from 283.5 K to 287.5 K and pressures from 0.76 MPa to 2.23 MPa. The results show that the carbon dioxide selectivity is moderately enhanced when cyclopentane is present in the mixed hydrate phase. Carbon dioxide could be enriched in the hydrate phase by attaining a mole fraction of up to 0.937 when the corresponding mole fraction in the gas mixture amounts to 0.507. When compared to the three phase hydrate–aqueous liquid–vapor equilibrium in the ternary system {water + carbon dioxide + nitrogen}, the equilibrium pressure of the mixed hydrate is reduced by 0.95 up to 0....

Spherical Monovalent Ions at Aqueous Liquid–Vapor Interfaces: Interfacial Stability and Induced Interface Fluctuations

Ion-specific interfacial behaviors of monovalent halides impact processes such as protein denaturation, interfacial stability, and surface tension modulation, and as such, their molecular and thermodynamic underpinnings garner much attention. We use molecular dynamics simulations of monovalent anions in water to explore effects on distant interfaces. We observe long-ranged ion-induced perturbations of the aqueous environment, as suggested by experiment and theory. Surface stable ions, characterized as such by minima in potentials of mean force computed using umbrella sampling MD simulations, induce larger interfacial fluctuations compared to nonsurface active species, conferring more entropy approaching the interface. Smaller anions and cations show no interfacial potential of mean force minima. The difference is traced to hydration shell properties of the anions, and the coupling of these shells with distant solvent. The effects correlate with the positions of the anions in the Hofmeister series (acknowledging variations in force field ability to recapitulate essential underlying physics), suggesting how differences in induced, nonlocal perturbations of interfaces may be related to different specific-ion effects in dilute biophysical and nanomaterial systems.

Temperature Dependence and Energetics of Single Ions at the Aqueous Liquid–Vapor Interface

We investigate temperature-dependence of free energetics with two single halide anions, I(-) and Cl(-), crossing the aqueous liquid-vapor interface through molecular dynamics simulations. The result shows that I(-) has a modest surface stability of 0.5 kcal/mol at 300 K and the stability decreases as the temperature increases, indicating the surface adsorption process for the anion is entropically disfavored. In contrast, Cl(-) shows no such surface state at all temperatures. Decomposition of free energetics reveals that water-water interactions provide a favorable enthalpic contribution, while the desolvation of ion induces an increase in free energy. Calculations of surface fluctuations demonstrate that I(-) generates significantly greater interfacial fluctuations compared to Cl(-). The fluctuation is attributed to the malleability of the solvation shells, which allows for more long-ranged perturbations and solvent density redistribution induced by I(-) as the anion approaches the liquid-vapor interface. The increase in temperature of the solvent enhances the inherent thermally excited fluctuations and consequently reduces the relative contribution from anion to surface fluctuations, which is consistent with the decrease in surface stability of I(-). Our results indicate a strong correlation with induced interfacial fluctuations and anion surface stability; moreover, resulting temperature dependent behavior of induced fluctuations suggests the possibility of a critical level of induced fluctuations associated with surface stability.

Solvation structure and energetics of single ions at the aqueous liquid–vapor interface

Potentials of mean force for single, nonpolarizable monovalent halide anions and alkali cations are computed for transversing the water–air interface (modeling using polarizable TIP4P-FQ and TIP4P-QDP). Iodide and bromide in TIP4P-FQ show interfacial stability, whereas chloride, bromide, and iodide show interfacial stability in TIP4P-QDP. A monotonic decrease in coordination number and an increasingly anisotropic distribution of solvating water molecules is shown to accompany movement of the ions towards vapor conditions; these effects are most noticeable with increases in ion size/decreases in magnitude of hydration free energy.

Is the Palea Kavala Bi–Te–Pb–Sb ± Au district, northeastern Greece, an intrusion-related system?

Intrusion-related gold systems are generally characterized by a Au–Bi–Te ± Sn–W metal assemblage genetically linked to the emplacement of granitoids. The Palea Kavala ore system, Greece, consists of ~ 150 minor Fe–Mn (Pb ± Zn ± Ag), Fe–Mn–Au, Fe–As–Au, Fe–Cu–Au, and Bi–Te–Au occurrences that occur primarily in quartz–calcite–sulfide veins (hypogene mineralization), or as supergene bodies, in overlapping zones centered on the ~ 21–22 Ma granodioritic Kavala pluton, which intrudes metamorphic rocks of the Paleozoic Rhodope metamorphic core complex. The pluton consists mostly of granodiorite with lesser amounts of diorite, tonalite and monzodiorite, which was emplaced along the regional E–W trending Kavala–Komotini fault. The recently discovered, ~ 4 km long, E–W trending so-called Kavala vein is a sheeted quartz vein system of Bi–Te–Pb–Sb ± Au mineralization that crosscuts the Kavala pluton and the schists and gneisses of the Rhodope Massif. The Kavala vein system is comprised of quartz with lesser amounts of K-feldspar, plagioclase and muscovite. Quartz–sericite–pyrite alteration is pervasive but minor kaolinite is also present. Pyrite (~ 5% of vein volume) contains inclusions of tetradymite (some gold-bearing), bismuthinite, and cosalite. Sulfur isotope values (n = 27) of pyrite from the Kavala and Chalkero veins, as well as pyrite and galena from Garizo Hill Fe–Mn–Pb vein range from − 1.9 to 1.0‰ (with one outlier of − 4.6‰) and suggest a magmatic sulfur source. Homogenization temperatures (T h) of type I (two-phase aqueous liquid–vapor) and type II (three-phase, H 2O–CO 2-rich) fluid inclusions that homogenize into the liquid phase in quartz from the Kavala and Chalkero veins range from 216.0° to 420.0 °C (n = 216) and 255.7° to 414.0 °C (n = 112), respectively. The T h of type III (two-phase aqueous liquid–vapor), which homogenize into the vapor phase, ranges from 210.4° to 323.4 °C (n = 28). The salinities of type I and type II inclusions range from 15.9 to 22.6 wt.% NaCl equiv. and 5.5 to 11.2 wt.% NaCl equiv., respectively. Eutectic temperatures of − 58.5° to − 44.3 °C for type I inclusions suggest the presence of appreciable CaCl 2 in addition to NaCl. Clathrate melting temperatures for type II inclusions of ~−56.7 °C indicate that CO 2 is the major component of the gaseous phase, however up to ~ 6% CH 4 is present in some inclusions. The presence of a zoned metallogenetic district centered on Bi–Te–Pb–Sb ± Au mineralization within the Kavala pluton, the presence of both magnetite and ilmenite in the Kavala pluton, and the two high-temperature, high-salinity, immiscible carbonic and aqueous fluids associated with the Kavala and Chalkero veins are consistent with them being part of an intrusion-related gold system that formed along the ilmenite–magnetite buffer.

Experimental measurement of the solubility of bismuth phases in water vapor from 220°C to 300°C: Implications for ore formation

Abstract Preliminary measurements were carried out of the solubility of the O 2- buffering assemblage bismuth + bismite (Bi 2 O 3 ) in aqueous liquid–vapor and vapor-only systems at temperatures of 220, 250 and 300 °C. All experiments were carried out in Ti reaction vessels and were designed such that the Bi solids were contained in a silica tube that prevented contact with liquid water at any time during the experiment. Two blank (no Bi solids present) liquid–vapor experiments at 220 °C yielded Bi concentrations (±1 σ ) in the condensed liquid of 0.22 ± 0.02 mg/L, whereas the solubility measurements at this temperature yielded an average value of approximately 6 ± 9 mg/L, with replicate experiments ranging from 0.3 to 26 mg/L. Although the 6 mg/L value is associated with a considerable degree of uncertainty, the experiments do indicate transport of Bi through the vapor phase. Measured Bi concentrations in the condensed liquid at 250 °C were in the same range as those at 220 °C, whereas those at 300 °C were significantly lower (i.e., all below the blank value). Vapor-only experiments necessarily contained much smaller initial volumes of water, thereby making the results more susceptible to contamination. Single blank runs at 220 and 300 °C yielded Bi concentrations of 82 and 16 mg/L, respectively. Measured concentrations (±1 σ ) of Bi in the vapor-only solubility experiments at 220 °C were 235 ± 78 mg/L for an initial water volume of 0.5 mL, and at 300 °C were 56 ± 30 mg/L and 33 ± 21 for initial water volumes of 1 and 2 mL, respectively, suggesting strong preferential partitioning of Bi into the vapor. The results indicate a negative dependence of Bi solubility on temperature, but are inconclusive with respect to the dependence of Bi solubility on water density or fugacity. The experiments reported here suggest that significant Bi transport is possible in the vapor phase. Comparison of the liquid–vapor and vapor-only experiments further suggests that, at the conditions studied, the solubility of Bi in the vapor is significantly higher than that in the liquid phase (calculated distribution coefficients, i.e., C Vapor / C Liquid at 220 °C ranged from 81 to 168, where C is concentration in mg/L). The concentrations measured in the vapor-only experiments at 220 °C are approximately 11 orders of magnitude higher than those calculated from available thermodynamic data assuming no interaction between volatile Bi species and water molecules. This finding indicates that hydration of volatile Bi species probably occurs to a significant extent; similar to behavior observed previously in published vapor phase solubility studies of other metals. However, the interpretation of the results was complicated by the formation of Bi silicate phases and the lack of certainty that O 2 fugacity buffering was effective throughout the experiments.

Structure of the Methanol Liquid−Vapor Interface: A Comprehensive Particle-Based Simulation Study

This research addresses a comprehensive particle-based simulation study of the structural, dynamic, and electronic properties of the liquid-vapor interface of methanol utilizing both ab initio (based on density functional theory) and empirical (fixed charge) models. Numerous properties such as interfacial width, hydrogen bond populations, dipole moments, and correlation times are characterized with identical schemes to draw useful conclusions on the strengths and weakness of the proposed models for the interface of neat methanol. Our findings indicate that all models considered in this study yield similar results for the radial distribution functions, hydrogen bond populations, and orientational relaxation times. Significant differences in the models appear when examining both the dipole moments and surface relaxation near the aqueous liquid-vapor interface. Here, the density functional theory interaction potential predicts a significant decrease in the molecular dipole moment and slight expansion in the oxygen-oxygen distance as the interface is approached. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE. For submission to Journal of Physical Chemistry B

REE Daughter Minerals Trapped in Fluid Inclusions in the Giant Bayan Obo REE-Nb-Fe Deposit, Inner Mongolia, China

The Bayan Obo REE-Nb-Fe deposit hosts the world's largest known REE resource. The deposit consists of replacement bodies hosted in dolomite marble and of magnetite, REE fluorocarbonates, fluorite aegirine, amphibole, calcite, and barite. Three types of fluid inclusions have been recognized: two-phase aqueous liquid-vapor (L-V), two- to three-phase CO2 (C), and three-phase liquid-vapor-solid (L-V-S) inclusions. Microthermometry measurements indicate that the carbonic phase in C inclusions is nearly pure CO2. During heating experiments, hexagonal or irregular-shaped daughter minerals in L-V-S inclusions complete dissolution at temperatures of 420-480°C and recrystallize again at about 400-320°C. These show that daughter minerals in multiphase inclusions in mineralizing veins were crystallized from trapped fluids, and are real daughter minerals. REE-carbonates, halite, sylvite, barite, calcite, and pyroxene (?) have been identified on the basis of crystal habit (microscopic and SEM) and EDX analysis. By comparison with Raman spectra of reference REE-carbonate mineral crystals, hexagonal or irregular-shaped daughter minerals in L-V-S inclusions might be cebaite and bastnaesite. The presence of REE-carbonates as an abundant solid in the ore-forming veins shows that the original oreforming fluids were very rich in REE, and therefore had the potential to produce economic REE ores at Bayan Obo.

Experimental Investigation and Calculation of Methane Hydrate Formation Conditions in the Presence of Ethylene Glycol and Sodium Chloride

Experimental three-phase hydrate equilibrium data (aqueous liquid solution, vapor, and incipient solid hydrate) for methane hydrates in aqueous solutions of ethylene glycol and sodium chloride are presented. The data are obtained in the temperature range of (262 to 282) K and pressure range of (2.1 to 9.5) MPa. The incipient hydrate formation pressures are also calculated using the recently developed equation-of-state method of Clarke and Bishnoi. The computed results are compared with the experimental data.

An ab initio molecular dynamics study of the aqueous liquid-vapor interface.

We present an ab initio molecular dynamics simulation of the aqueous liquid-vapor interface. Having successfully stabilized a region of bulk water in the center of a water slab, we were able to reproduce and further quantify the experimentally observed abundance of surface "acceptor-only"(19%) and "single-donor"(66%) moieties as well as substantial surface relaxation approaching the liquid-vapor interface. Examination of the orientational dynamics points to a faster relaxation in the interfacial region. Furthermore, the average value of the dipole decreases and the average value of the highest occupied molecular orbital for each water molecule increases approaching the liquid-vapor interface. Our results support the idea that the surface contains, on average, far more reactive states than the bulk.

Equilibrium conditions for the hydrogen sulfide hydrate formation in the presence of electrolytes and methanol

AbstractNatural gas industry encounters systems that consist of gases like CO2 and H2S, and aqueous solutions of methanol and mixed electrolytes. A knowledge of the phase behavior of such systems, including hydrate formation, is essential in gas production and the design of facilities for gas transportation and processing. Recently, Dholabhai et al. (1997, 1996) and Bishnoi and Dholabhai (1998) described equilibrium conditions for CO2 and gas mixtures containing CO2 in the presence of methanol, electrolytes and ethylene glycol. In the present work aqueous three phase (aqueous liquid solution, vapor and incipient hydrate) equilibrium conditions of H2S hydrate formation in aqueous solutions of electrolytes and methanol are measured in the temperature range of 272 to 294 K and pressure range of 0.3 to 1.0 MPa. A ‘full view’ sapphire variable volume cell with a movable piston is used to obtain the experimental data.