Nernst Partition Coefficients Research Articles

Uranium partitioning between apatite and hydrothermal fluids at 150–250 °C

This experimental study is focused on the immobilization of dissolved uranium (U) via its entrapment by apatite at hydrothermal conditions. Experiments on apatite crystallization were conducted in 0.5 M sodium chloride (NaCl) solutions at temperatures of 150, 200, and 250 °C. Uranium was introduced into the system as a solid compound (UO3), which controlled the concentration of dissolved U in the hydrothermal fluids. The results showed that U contents in apatite exceed U concentrations in co-existing fluid by 2–3 orders of magnitude. Apparent Nernst partition coefficients (DU) and exchange coefficient (KU/Ca) were evaluated. Experimentally determined DU values were consistent with DU predicted by the Lattice Strain Model at 200 and 250 °C. The obtained KU/Ca values shows dependence on temperature. The results lay the foundation for further assessment of uranium immobilization in apatite and other minerals at repository conditions.

Uranium uptake by phosphate minerals at hydrothermal conditions

The goal of this work was to evaluate the immobilization of uranium (U) through crystallization of calcium phosphate minerals (phosphates), which have a strong ability to absorb and retain dissolved uranyl, and therefore, are useful in various geological and environmental applications. To date, most of the experimental studies have been conducted at room temperature and high temperature assessments on uranium immobilization rely on the extrapolation procedure, which is not always accurate. To evaluate uranium partition coefficients between phosphates and hydrothermal fluid, we performed a series of crystallization experiments at 25–350 °C and various aqueous uranium concentrations.Crystallization occurred through the transformation of brushite to monetite or/and apatite in aqueous solutions doped with uranium aliquots. Solid products were extracted and characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The local bonding environment and valence state of uranium in apatite were determined via X-ray absorption spectroscopy (XAS). Uranium concentration in crystals and coexisting solutions were measured with inductively coupled plasma mass spectrometry (ICP-MS). Apparent partition coefficients were calculated as Nernst partition coefficients (DU) and Doener-Hoskins partition coefficients (KD−HU/Ca) (to account for closed reservoir effect). Experimental DU values were compared with those calculated using the lattice strain model. Results showed that >92% of U added to solutions was extracted via this crystallization method and KD−HU/Ca decreases with increasing phosphate crystallization temperature. Thus, phosphates, especially apatite, has a strong potential to immobilize uranium under hydrothermal conditions and can be used in the development of engineering barriers to further improve the efficiency of existing backfill materials in the disposal of nuclear waste.

Trace element partitioning coefficients between terrestrial silicate melts and plagioclase feldspar: Improved and simplified parameters

Nernst partition coefficient data are compiled and parameterized against commonly measured and petrologically significant Input Variables, allowing plagioclase/meltD values for 37 trace elements to be calculated. With few exceptions plagioclase/meltDs increase with decreasing temperature, anorthite-content of plagioclase (An), wt% melt MgO and FeO* (all iron as FeO), molar melt Mg/(Mg + Fetotal); and with increasing wt% melt SiO2 and Na2O + K2O. High field strength cations and rare earth elements (REE) with similar ionic radii have nearly fixed ratios of LnD (e.g. LnDLa/LnDCe). These can be linked as a chain to construct a nearest-neighbour plagioclase/meltDREE (NN-DREE) profile from a point of origin at DCe. Correlations between LnDCe and An content in the partitioning data were regressed to connect these variables algebraically. Analysis of these NN-DREE profiles with the Lattice Strain Model (LSM) requires a temperature value, which was pre-defined by fitting simplified temperature-An paths to experimental data binned for melt H2O content. In the LSM, r3+0 is the size of the site into which REE substitute. Three published r3+0 parameterizations were tested. The Dohmen and Blundy (2014) parameterization of r3+0 [Å] (r3+0 = 1.331 − 0.067An) yielded the best fits to the NN-DREE profiles when values of D3+0 and E3+M were optimized. D3+0 is the strain compensated partition coefficient and E3+M is Young’s Modulus of the M-site hosting REE. Starting from the preferred r3+0 parameterization, NN-DREE profiles at many An contents were fit with a LSM by varying D3+0 and E3+M. These multiple fits yielded a tight linear trend of increasing LnD3+0 with decreasing An content [LnD3+0 = (−2.8323An) – 0.0538] applicable to all three temperature-An functions. Previously proposed parameterizations of Young’s Modulus E3+M can reproduce DREE profiles of very calcic plagioclase (>An0.9), but yield profiles that are too steep to fit DREE profiles of more sodic compositions. The LSM fits for dry melts (H2O < 1%) yield a trend of linearly-decreasing LnE3+M with decreasing An content [LnE3+M = (1.2808An) + 3.4897]. The temperature-An functions for wet (1–5% H2O) and very wet (>5% H2O) melts yield similar LnE3+Mvs An trends, but at lower LnE3+M to compensate for lower temperatures. With these parameterizations of temperature, r3+0, D3+0 and E3+M, the NN-DREE Lattice Strain Model reproduces the increasingly flatter and higher DREE profiles of plagioclase crystallizing from basaltic to rhyolitic melts, with An-content as the sole Input Variable needed.

Highly efficient extractive desulfurization by specific functionalized porous ionic liquids via C-H···π interactions

Porous ionic liquids (PILs) are an emerging class of materials that possess the porosity of solids and the fluidity of liquids, which have shown great potential in separation. Herein, a novel kind of silica-based porous ionic liquids (OS-PIL) functionalized with quaternary ammonium salt was successfully synthesized to remove the dibenzothiophene (DBT) in the model fuel. The OS-PIL exhibit high extraction activity and its Nernst partition coefficient could reach up to 4.22. The experimental results indicated that a synergistic effect between porous materials and ionic liquids as well as the multiple sites in quaternary ammonium salt greatly contributed to the high extractive desulfurization efficiency. Moreover, density functional theory (DFT) calculations and spectroscopic investigations were employed to gain in-depth insights into the extraction mechanism. The results demonstrated that the porous structure and ion pair of OS-PIL exhibit stronger interaction for DBT, in which the C-H···π is dominant. These kinds of PILs with highly specific surface areas and multiple active sites will have good application prospects in the field of extractive desulfurization.

Sustained Release of a Polymeric Wetting Agent from a Silicone-Hydrogel Contact Lens Material.

Uptake and release kinetics are investigated of a dilute aqueous polymeric-surfactant wetting agent, (ethylene oxide)45—(butylene oxide)10 copolymer, also referred to as poly(oxyethylene)-co-poly(oxybutylene), impregnated into a newly designed silicone-hydrogel lens material. Transient scanning concentration profiles of the fluorescently tagged polymeric surfactant follow Fick’s second law with a diffusion coefficient near 10–11 cm2/s, a value 3–4 orders smaller than that of the free surfactant in bulk water. The Nernst partition coefficient of the tagged polymeric wetting agent, determined by fluorescence microscopy and by methanol extraction, is near 350, a very large value. Back-extraction of the polymeric-surfactant wetting agent releases only ∼20% of the loaded amount after soaking the fully loaded lens for over 7 days. The remaining ∼80% is irreversibly bound in the lens matrix. Reverse-phase liquid chromatography of the lens-loaded and lens-extracted surfactant demonstrates that the released wetting agent is more hydrophilic with a higher polarity. Aqueous poly(oxyethylene)-co-poly(oxybutylene) is hypothesized to attach strongly to the lens matrix, most likely to the lens silicone domains. Strong binding leads to slow transient diffusion, to large uptake, and to significant irreversible retention. These characteristics indicate the suitability of using a poly(oxyethylene)-co-poly(oxybutylene) nonionic polymeric surfactant to maintain enhanced lens wettability over time. Methodology and findings from this study provide useful insights for designing sustained-release contact-lens wetting agents and materials.

Molecular dynamics simulation of extractive desulfurization of diesel oil model using magnetic ionic liquids

This paper serves as a molecular dynamics (MD) study on the desulfurization of diesel oil model using magnetic ionic liquids (MILs). In this regard, three different MILs, namely, [emim][FeCl4], [bmim][FeCl4] and [hmim][FeCl4] have been used to remove the dibenzothiophene (DBT) from n-dodecane as diesel oil model. The effects of alkyl chain length of cation in MIL, temperature, initial sulfur content and mass ratio of MIL to diesel oil on two vital parameters of desulfurization process i.e. percentage of S-removal and Nernst partition coefficient (KN) were investigated. These two parameters were calculated based on the method proposed by Feng and Mi (Ind. Eng. Chem. Res. 2014, 53, 20234-20240), in which they used the radial distribution function (RDF) plots obtained by Conductor-like Screening Model for Real Solvents (COSMO-RS) to evaluate the desulfurization of fuel oil, quantitatively. Our results showed that the [bmim][FeCl4] has the highest DBT-philisity and its S-removal efficiency increases with increasing temperature and the concentration of the MIL. Furthermore, from the investigation of the initial sulfur content in diesel oil model it is concluded that the MIL can be a good extractor for oil refinery applications with a wide range of sulfur content in diesel oil. The results of RDF and combined distribution function (CDF) plots and also Voronoi tessellation analysis showed that the DBT molecules are adsorbed mainly by the MIL molecules compared with the n-dodecane which leads to DBT-removal. Also, it is found that the DBT molecules interact with the cation of MIL more than its anion. The results of domain analysis showed that the n-dodecane subset is stiffer than the MIL and DBT subsets. Altogether, the Fe-containing MILs can be a good sulfur extractor with high S-removal efficiency, lower toxicity than common volatile organic solvents, and low cost compared to the other common methods such as hydrodesulfurization (HDS), for future oil refinery applications.

Extractive desulfurization of diesel fuel by amide-based type IV deep eutectic solvents

As promising green alternative solvents for ionic liquids, deep eutectic solvents (DESs) have been widely used in separation, catalysis, synthesis, etc. Most of the researches have focused on the application of DESs formed by hydrogen bonding interaction. In this paper, amide-based type IV DESs were synthesized from metal chloride and amides with coordination interaction, and they were used for extractive desulfurization of fuels. The experimental results showed the DES ZnCl2/N-methylformanilide (ZnCl2/MFA) had the highest desulfurization efficiency with the Nernst partition coefficient (KN) as 2.41. The extraction mechanism was firstly explored by Fourier transform infrared spectrometer (FT-IR) and 1H nuclear magnetic resonance (1H NMR). Then density functional theory (DFT) study suggested that π-π interactions and CH···π interactions contribute mainly to effective removal of DBT from fuel oil by DESs.

An inexpensive N-methyl-2-pyrrolidone-based ionic liquid as efficient extractant and catalyst for desulfurization of dibenzothiophene

Inexpensive N-methyl-pyrrolidone (NMP)-based ionic liquids (ILs) are synthesized by coordinating N-methyl-pyrrolidone with anhydrous FeCl3 or ZnCl2. The introduction of metal chlorides lowers the solubility of NMP for actual diesel. The obtained C5H9NO·0.3FeCl3 IL shows remarkable extraction ability for dibenzothiophene (DBT) with Nernst partition coefficients (kN) above 7.5, which can be attributed to its low viscosity and bifunctional extractive groups of five-membered ring of NMP and unoccupied orbitals of Fe ion. The oxidative desulfurization of DBT using H2O2 as oxidant and ILs as extractants are investigated. The scavenger experiments and electron paramagnetic resonance (EPR) measurement verify the active species is hydroxyl radical (OH) responsible for the oxidation of DBT. FeCl3-based ILs show much better effects in catalyzing H2O2 to generate OH than ZnCl2-based ILs. The process and mechanism for extraction and catalytic oxidation of DBT in an oil–ionic liquid–H2O2 system are proposed. The C5H9NO·0.3FeCl3 IL shows excellent recycling performance. After six-run experiment, there is only little loss in activity, which can be ascribed to the high solubility (18,190ppm) of dibenzothiophene-sulfone (DBTO2), the main oxidation product of DBT, in the IL.

Temperature-responsive ionic liquid extraction and separation of the aromatic sulfur compounds

Extraction of aromatic sulfur compounds from model oil using a temperature-responsive ionic liquid (IL) N-butyl-N-methylpiperidinium tetrachloroferrate ([C4mpip]FeCl4) as extractant has been investigated. In the extractive desulfurization process, liquid–liquid equilibrium was obtained at 45°C for 10min. After the extraction system was cooled to room temperature, the IL returned to solid due to the reversible thermoregulated phase transition of the IL. Therefore, it was easy for separation of oil and solid [C4mpip]FeCl4. The extraction efficiency and Nernst partition coefficient (KN) could get to 45.5% and 2.92, respectively, after a single extraction of DBT. Some important factors, such as extraction temperature, the amount of IL, initial sulfur content, multiple extractions, reusability and the mutual solution were investigated. The extraction ability of different sulfur compounds followed the order DBT>BT>4,6-DMDBT. Finally, the extraction mechanism was studied systematically with experimental and theoretical methods. Compared with the extraction abilities of another three ILs, [C8mpip]FeCl4, [C12mpip]FeCl4 and [C4Py]FeCl4, the size and aromatic structure of cation may be two positive factors but not the main extraction mechanism. The coordination interaction between Fe atom of IL and S atom of DBT was confirmed by IR spectra and theoretical computation.

In situ study of boron partitioning between calcite and fluid at different crystal growth rates

The boron isotopic and chemical content of carbonates (expressed as δ11B and B/Ca ratios) have been proposed as proxies for seawater carbonate system parameters. Thermodynamic and kinetic effects on δ11B and B partitioning are not yet fully constrained, underscoring the importance of exploring possible effects of growth rate on boron incorporation in synthetic calcium carbonate minerals, which is the focus of this study. Secondary Ion Mass Spectrometry (SIMS) measurements of B/Ca and δ11B were performed on single crystal of calcite synthesized by diffusion of CO2 under controlled conditions from a solution of NH4Cl–CaCl2 doped with boron. Growth rates of calcite (V, nm/s) within crystals grown isothermally at 24.6°C were monitored by sequentially spiking calcite-precipitating fluids with rare earth element (REE) dopants. The REE were analyzed with SIMS at spots that match those locations where B/Ca and δ11B ratios were measured. Values for the boron Nernst partition coefficient, defined as DB=B(calcite)/B(fluid), increase from 0.5 (pHNBS=8.15) to 0.9 (pH=8.00) with values of V increasing from 0.04 to 0.13nm/s. For δ11B behavior, it was not possible to draw conclusive results due to the analytical error (2.2‰; 2σ). pH effects on DB during calcite precipitation, associated with an increase in pH from 8.00 to 8.15, appear to be masked by the competing effects of changing V. We conclude that over the range of growth rates and other conditions investigated in this study, growth rate effects on B partitioning need to be accounted for when using B/Ca ratios in biogenic calcite as a proxy for seawater carbonate system parameters.

Desulfurization of Real Fuel Oils by Extraction with Ionic Liquids

Aromatic 1-butyl-3-methylimidazolium dicyanamide ([C4mim][N(CN)2]) and 1-ethyl-3-methylimidazolium dicyanamide ([C2mim][N(CN)2]) ionic liquids are tested for their performance in the extractive desulfurization of real FCC gasoline and diesel fuel. [C4mim][N(CN)2] has proven to be more effective than [C2mim][N(CN)2] in removing sulfur from fuels and was thus selected to undergo a series of further tests. A competitive desulfurization efficiency of nearly 40% and 30% was realized with [C4mim][N(CN)2] for diesel fuel and gasoline, respectively, in a single extraction at <1 h, 25°C, and 1:1(w/w)IL:fuel. The influence of IL:fuel mass ratio, temperature, and multiple extractions on S-extraction efficiency is investigated, and the result tends to favor large-scale industrial application. This high efficiency obtained at low temperature, together with the insensitivity of the Nernst partition coefficient on desulfurization efficiency, is industrially favorable because not much energy and cost are required. The influence of mass ratios is not obvious, but to some degree, the Nernst partition coefficients depend on the mass ratio, suggesting that this extraction is not a completely physically-determined extraction. This work offers a significant contribution to the production of clean oils by extraction with ionic liquids.

Effective and Intrinsic Kinetics of the Two-Phase Alkylation of i-Paraffins with Olefins Using Chloroaluminate Ionic Liquids As Catalyst

Acidic ionic liquids (IL) are attractive alternative catalysts in refinery alkylation of i-paraffins with light olefins, but the intrinsic kinetics and influence of mass transfer on the effective kinetics in this biphasic system is still unknown. Solubility measurements were conducted (largely with neutral, nonacidic ILs) using mixtures of i-hexane/2-hexene and i-pentane/2-pentene, respectively, to determine the Nernst partition coefficient and thus the maximum concentration of olefins and paraffins in the IL. Thereafter, kinetic studies were carried out both in a stirred and nonstirred batch reactor using i-hexane/1-hexene and i-pentane/1-pentene. In the static system, the concentration profile of the particular olefin in the organic phase was measured. The experimental results are in good agreement with the simulation based on the interplay of the chemical reaction in the ionic liquid as well as of the external and internal mass transfer to the interface and into the IL. The effective reaction rate of a...

Deep extractive and oxidative desulfurization of dibenzothiophene with C5H9NO·SnCl2 coordinated ionic liquid

A new C5H9NO·SnCl2 coordinated ionic liquid (IL) was prepared by reacting N-methyl-pyrrolidone with anhydrous SnCl2. Desulfurization of dibenzothiophene (DBT) via extraction and oxidation with C5H9NO·SnCl2 IL as extractant, H2O2 and equal mol of CH3COOH as oxidants was investigated. The Nernst partition coefficients kN of C5H9NO·SnCl2 IL for the DBT in n-octane was above 5.0, showing its excellent extraction ability. During the oxidative desulfurization process, the optimal molar ratio of H2O2/DBT was six. Sulfur removal of DBT in n-octane was 94.8% in 30min at 30°C under the conditions of H2O2/DBT molar ratio of six and V (IL):V (oil)=1:3. Moreover, the sulfur removal increased with increasing temperature because of the high reaction rate constant, low viscosity, and high solubility of dibenzothiophene-sulfone in the IL. The kinetics of oxidative desulfurization of DBT was also investigated, and the apparent activation energy was found to be 32.5kJ/mol. The IL could be recycled six times without a significant decrease in activity.

Eluted substances from unpolymerized and polymerized dental restorative materials and their Nernst partition coefficient

Components released from resin-based dental materials are important factors in the assessment of the biocompatibility of these materials. The study was performed to investigate the elution of substances from unpolymerized and polymerized composites (Tetric=TET; Arabesk=ARA), ormoceres (Admira)=ADM; Definite=DEF) and the compomere (Hytac=HYT). Specimens were polymerized and immersed in either water or methanol. Besides the unpolymerized specimens were dissolved in methanol. Eluted substances were detected by gas chromatography/mass spectroscopy. The Nernst partition coefficient (DC) of 64 substances, eluted from various resin-based dental materials was determined. Only in methanolic and aqueous eluates from unpolymerized and polymerized specimens of DEF and ADM, the comonomere 1,2/1,3-glycerol dimethacrylate was measured. Triethylene glycol dimethacrylate was eluted into the aqueous and methanolic phase from polymerized specimens from TET and ARA. 2-Hydroxyethyl methacrylate was eluted into the methanolic phase from polymerized specimen from TET and HYT. Residuals of monomer synthesis like triphenyl stibane were found in unpolymerized specimens of TET and ARA. Camphorquinone was eluted into the methanolic eluate from polymerized and unpolymerized specimens from all tested dental materials. Highest DC of 20.8 was found for 1/2-cyclohexene methacrylate. DC of urethane dimethacrylate and bisphenol-A-glycidyldimethacrylate varies from different manufacturers. Impurities from manufacturing process were found in some resin-based materials. Various well-known substances causing allergic reactions were found in aqueous or methanolic elutes. Patients, dental and manufacturing personnel are exposed to these substances.

Cr-spinel/olivine and Cr-spinel/liquid nickel partition coefficients from natural samples

The Nernst partition coefficient of nickel ( D Ni) between Cr-spinel and silicate melt in natural systems has been investigated using mid-ocean ridge basalts (MORB) and other volcanic rocks. The Cr-spinel/olivine D Ni values in volcanic rocks are between 1.2 and 0.3, indicating that the Cr-spinel/liquid D Ni values vary from slightly higher to significantly lower than the olivine/liquid D Ni values in natural systems. The Cr-spinel/liquid D Ni values from the MORB samples vary between 6 and 11, slightly higher than those from the S-bearing experiments of Satari et al. [Satari P., Brenan J. M., Horn I. and McDonough W. F. (2002) Experimental constraints on the sulfide- and chromite–silicate melt partitioning behavior of rhenium and platinum-group elements. Economic Geology 97, 385–398]. The results of the MORB samples and the experiments of Satari et al. (2002) indicate a negative correlation between the Cr-spinel/liquid D Ni and the X Cr values in Cr-spinels (Cr cation number on the basis of 3 total cations in the spinel structure). Variations of Cr-spinel/liquid D Ni values with Cr-spinel compositions can be estimated from an empirical equation based on the results of the MORB samples and the experiments by Satari et al. (2002). The choice of Cr-spinel/liquid D Ni = 10 for numerical modeling by Righter et al. [Righter K., Leeman W. P. and Hervig R. L. (2006) Partitioning of Ni, Co, and V between spinel-structured oxides and silicate melts: importance of spinel composition. Chemical Geology 227, 1–25] is reasonable for basaltic systems. For picritic and komatiitic systems a lower value of ∼5 is more appropriate.

Trace element partitioning coefficients between silicate melts and orthopyroxene: Parameterizations of D variations

Nernst partition coefficient data between orthopyroxene and silicate melts show variability for most trace elements which cannot be neglected when designing petrogenetic trace element models. Orthopyroxene/Liquid D data were examined for variation against pressure, temperature; orthopyroxene (Opx) wollastonite content (Wo = 100 × Ca/Ca + Mg + Fe), mg# (Mg/Mg + Fe total), and tetrahedral Al (Al iv) content; and wt.% melt SiO 2, Al 2O 3, FeO, MgO, H 2O and MgO# (MgO/MgO + FeO total). For most elements, Opx/Liquid D values correlate best against melt LnMgO (wt.%) content, Opx mg#, and melt SiO 2, with most Opx/Liquid D values increasing as LnMgO and Opx mg# decrease and as SiO 2 increases. Variations of Opx/Liquid D with other factors show more diffuse patterns. The effect of pressure is important for Opx/Liquid D Na and D Cs. Log f O2 may be important in constraining Opx/Liquid D V. Multiple regression analysis of combinations of these input variables generally yields better solutions, although in most cases the simple regressions against LnMgO or Opx mg# capture most of the variance. Multi-element Opx/Liquid D profiles calculated from Opx/Liquid D regressions against melt MgO and SiO 2 content, Opx mg#, and multiple regression analysis of melt and mineral compositional variables, are compared to results of the Lattice Strain Model; generating parameterizations of D 0 (the strain compensated partition coefficient), E 3+ M (Young's Modulus), and r 0 (the size of the M site), which can be used to calculate Opx/Liquid D values for the rare-earth elements (REE) and Y. These parameterizations of Opx/Liquid D variations yield results comparable to experimental or natural partitioning data, and provide better constrained solutions to trace element models applied to magma genesis and differentiation. Regressions were also performed to generate a number of orthopyroxene-saturation geothermometers, which are accurate to ca. 50°K. Variations of the Fe–Mg exchange coefficient were also parameterized.

Immiscible silicate liquid partition coefficients: implications for crystal-melt element partitioning and basalt petrogenesis

This study investigates partitioning of ele- ments between immiscible aluminosilicate and boro- silicate liquids using three synthetic mixtures doped with 32 trace elements. In order to get a good spatial separation of immiscible liquids, we employed a high- temperature centrifuge. Experiments were performed at 1,050-1,150� C, 1 atm, in sealed Fe and Pt containers. Quenched products were analysed by electron micro- probe and LA ICP-MS. Nernst partition coefficients (D's) between the Fe-rich and Si-rich aluminosilicate immiscible liquids are the highest for Zn (3.3) and Fe (2.6) and the lowest for Rb and K (0.4-0.5). The plots of D values against ionic potential Z/r in all the composi- tions show a convex upward trend, which is typical also for element partitioning between immiscible silicate and salt melts. The results bear upon the speciation and structural position of elements in multicomponent silicate liquids. The ferrobasalt-rhyolite liquid immis- cibility is observed in evolved basaltic magmas, and may play an important role in large gabbroic intrusions, such as Skaergaard, and during the generation of unusual lavas, such as ferropicrites.

Trace element partitioning in plagioclase feldspar

Compilation and interpretation of experimental and natural Nernst partition coefficient ( plagioclase/melt D) data show that, with a few exceptions, increases in plagioclase/melt D correlate with decreasing anorthite-content of plagioclase. In contrast, increases of plagioclase/melt D for Ga, Sc, Cu, Zn, Zr, Hf and Ti, are better correlated against decreasing melt MgO or increasing melt SiO 2 contents. plagioclase/melt D for Ti and the rare earth elements (REE) show little dependence on temperature, but increase as the melt water content increases. plagioclase/melt D for K and Sr are sensitive to pressure. Variations of D 0 (the strain compensated partition coefficient), r 0 (the size of the site into which REE substitute), and E (Young’s Modulus of this site) were parameterized against variations of melt SiO 2, the An-content of plagioclase, and other combinations of variables, allowing plagioclase/melt D REE-Y to be calculated from a variety of input parameters. The interrelations of temperature, melt MgO and SiO 2 content, and plagioclase anorthite-content for wet and dry systems were also parameterized to facilitate interpolation where such data are lacking. When combined, these semi-empirical parameterizations yield plagioclase/melt D results comparable to available experimental and natural data.

The solubility of platinum and gold in NaCl brines at 1.5 kbar, 600 to 800°C: A laser ablation ICP-MS pilot study of synthetic fluid inclusions

The concentration and distribution of Pt and Au in a fluid-melt system has been investigated by reacting the metals with S-free, single-phase aqueous brines (20, 50, 70 wt% eq. NaCl) ± peraluminous melt at a confining pressure of 1.5 kbar and temperatures of 600 to 800 °C, trapping the fluid in synthetic fluid inclusions (quartz-hosted) and vesicles (silicate melt-hosted), and quantifying the metal content of the trapped fluid and glass by laser ablation ICP-MS. HCl concentration was buffered using the assemblage albite-andalusite-quartz and f O 2 was buffered using the assemblage Ni-NiO. Over the range of experimental conditions, measured concentrations of Pt and Au in the brines ( C P t fluid , C A u f l u i d ) are on on the order of 1–10 3 ppm. Concentrations of Pt and Au in the melt ( C P t m e l t , C A u m e l t ) are ∼35–100 ppb and ∼400–1200 ppb, respectively. Nernst partition coefficients ( D P t f l u i d / m e l t , D A u f l u i d / m e l t ) are on the order of 10 2–10 3 and vary as a function of C m e t a l f l u i d (non-Henry’s Law behavior). Trapped fluids show a significant range of metal concentrations within populations of inclusions from single experiments (∼ 1 log unit variability for Au; ∼2–3 log unit variability for Pt). Variability in metal concentration within single inclusion groups is attributed to premature brine entrapment (prior to metal-fluid-melt equilibrium being reached); this allows us to make only minimum estimates of metal solubility using metal concentrations from primary inclusions. The data show two trends: (i) maximum and average values of C A u f l u i d and C P t f l u i d in inclusions decrease ∼2 orders of magnitude as fluid salinity ( m ∑ C l f l u i d ) increases from ∼4 to 40 molal (20 to 70 wt % eq. NaCl) at a constant temperature; (ii) maximum and average values of C A u f l u i d increase approximately 1 order of magnitude for every 100°C increase temperature at a fixed m ∑ C l f l u i d . The observed behavior may be described by the general expression: log ⁡ ( m m e t a l f l u i d , T , 1.5 k b a r ) = x ⋅ log ⁡ ( m ∑ C l f l u i d ) − y where x (slope of the solubility curve) is similar for both Au and Pt (−2), and y increases with increasing T. The strong negative correlation between salinity and metal concentration may result from (i) the “salting-out” of neutral hydrogen chloride complexes [e.g., PtCl 3H] as NaCl is added to the solution and free H 2O is consumed during the production of HCl 0 by the buffer assemblage, or (ii) the consumption of free H 2O by the hydration of non-chloride-based metal complexes such as hydroxides [e.g., Pt(OH) 2 · (H 2O) n ]. The proposed solubility mechanisms would be enhanced if activity coefficients for HCl and/or metal complexes decrease significantly with increasing fluid salinity. Identification of the exact dissolution mechanism at such extreme conditions and confirmation of the equilibrium metal concentrations awaits future study. The results of this pilot study demonstrate that single-phase hypersaline fluids which exsolve from or interact with residual magmatic liquids, partially crystallized rocks, or small volumes of PGE (platinum-group element)-Au-bearing sulfide can potentially dissolve and transport economically-significant amounts of Pt and Au across the magmatic-hydrothermal transition at moderately oxidizing conditions.

Partitioning coefficients between olivine and silicate melts

Variation of Nernst partition coefficients ( D) between olivine and silicate melts cannot be neglected when modeling partial melting and fractional crystallization. Published natural and experimental olivine/liquid D data were examined for covariation with pressure, temperature, olivine forsterite content, and melt SiO 2, H 2O, MgO and MgO/MgO + FeO total. Values of olivine/liquid D generally increase with decreasing temperature and melt MgO content, and with increasing melt SiO 2 content, but generally show poor correlations with other variables. Multi-element olivine/liquid D profiles calculated from regressions of D REE–Sc–Y vs. melt MgO content are compared to results of the Lattice Strain Model to link melt MgO and: D 0 (the strain compensated partition coefficient), E M 3+ (Young's Modulus), and r 0 (the size of the M site). Ln D 0 varies linearly with Ln MgO in the melt; E M 3+ varies linearly with melt MgO, with a dog-leg at ca. 1.5% MgO; and r 0 remains constant at 0.807 Å. These equations are then used to calculate olivine/liquid D for these elements using the Lattice Strain Model. These empirical parameterizations of olivine/liquid D variations yield results comparable to experimental or natural partitioning data, and can easily be integrated into existing trace element modeling algorithms. The olivine/liquid D data suggest that basaltic melts in equilibrium with pure olivine may acquire small negative Ta–Hf–Zr–Ti anomalies, but that negative Nb anomalies are unlikely to develop. Misfits between results of the Lattice Strain Model and most light rare earth and large ion lithophile partitioning data suggest that kinetic effects may limit the lower value of D for extremely incompatible elements in natural situations characterized by high cooling/crystallization rates.