Heat capacities of aqueous solutions of sodium hydroxide and water ionization up to 300 °C at 10 MPa

A commercial (Setaram C80) calorimeter has been modified to measure the heat capacities of highly caustic solutions at temperatures up to 300 °C and pressures up to 20 MPa. The improvements have allowed more accurate determination of the isobaric volumetric heat capacities of chemically aggressive liquids at high temperatures. Test measurements with aqueous solutions of sodium chloride showed a reproducibility of about ±0.1%, with an accuracy of ∼0.3% or better, over the whole temperature range. Heat capacities of aqueous solutions of sodium hydroxide at concentrations from 0.5 to 8 mol/kg were measured at temperatures from 50 to 300 °C and a pressure of 10 MPa. Apparent molar isobaric heat capacities of NaOH(aq) were calculated using densities determined previously for the same solutions by vibrating-tube densimetry. Standard state (infinite dilution) partial molar isobaric heat capacities of NaOH(aq) were obtained by extrapolation using an extended Redlich-Meyer equation. Values of the standard heat capacity change for the ionization of water up to 300 °C were derived by combining the present results with the literature data for HCl(aq) and NaCl(aq).     

The ion-pair constant and other thermodynamic properties of HCl up to 350°C

Solubilities of silver chloride in aqueous hydrochloric acid solutions have been determined from 100 up to 350°C. From these measurements, the ionisation constant of HC1 has been evaluated up to 225°C. Evidence is presented to show that a protonated silver species, HAgCl₂⁰, exists at 275°C and above. Available experimental data up to 200°C have been firted to Pitzer's equation to generate an algorithm to calculate stoichiometric activity and osmotic coefficients of HCl up to 350°C and concentrations up to at least 3.0 m. Using the present results and those of Wrightet al. (1961), Pearsonet al. (1963) and Lukashowet al. (1976), the dissociation constant (K_d) of HCl as a function of temperature is described by the equation log₁₀K = 2136.898 + 1.020349T−4.5045 × 10⁻⁴T²−50396.40/T−901.770 10g₁₀T (Tin °K) which is valid in the range 25–350°C. Calculated enthalpy (ΔH⁰), entropy (ΔS⁰) and heat capacity change (ΔC_p⁰) functions for HCl dissociation have been rationalized in terms of changing solute and solvent characteristics as temperature is raised.     

An XRD study of the crystal structure of gearksutite and its stability during heating to 300°C

The crystal structure of gearksutite, Ca and Al hydrofluoride CaAlF₄(OH) · H₂O, was refined using the Rietveld method with power diffraction data. The thermal stability of its crystal structure was studied for the first time using high-temperature XRD. Thermal XRD study of the mineral in the temperature range from 25 to 300°C revealed its stability to temperatures of 300-310°C. The mineral began to decay at temperatures greater than 300°C. The increase in the unit-cell parameters was established and the coefficients of thermal expansion were calculated.     

Amorphous silica solubilities IV. Behavior in pure water and aqueous sodium chloride,sodium sulfate,magnesium chloride,and magnesium sulfate solutions up to 350°C

Solubilities of amorphous silica were determined in separate aqueous solutions of sodium chloride, sodium sulfate, magnesium chloride, and magnesium sulfate at temperatures up to 350°C. These salts, of strong interest in hydrothermal oceanography and geothermal energy, generally ranged in concentration from zero to saturation. Solubilities in the sodium chloride solutions followed closely earlier observed decreases in sodium nitrate solutions at high temperatures.Amorphous silica solubilities were depressed most by magnesium chloride, followed by magnesium sulfate, and less by sodium chloride. As the temperature rose the relative decrease in solubility caused by added salt became smaller. Surprisingly, sodium sulfate solutions, showing little effect at 25°C, sharply raised the solubility as the temperature increased to 350°C. Plots of the logarithms of derived activity coefficients against molalities of added salt gave approximately straight lines. These plots allow simple predictions of amorphous silica solubility in single salt solutions.     

New, high-precision P–T estimates for Oman blueschists: implications for obduction, nappe stacking and exhumation processes

Oman blueschists and eclogites lie below the obduction nappe of the Semail ophiolite in one of the key areas on Earth for the study of plate convergence. Here new metamorphic and tectonic constraints are provided for the central, yet poorly constrained Hulw unit, sandwiched between the low‐grade units (～10 kbar, <300 °C) and the As Sifah eclogites (P_max ～ 23 kbar; T_max ～ 600 °C). TWEEQU multi‐equilibrium thermobarometry, using both compositional mapping and spot analyses, and Raman spectroscopy of carbonaceous material yield a high‐precision P–T path for the Hulw and As Sheikh units and reveal that they shared a common P–T history in four stages: (i) a pressure decrease from 10–12 kbar, 250–300 °C to 7–9 kbar, 300–350 °C; (ii) almost isobaric heating at ～8–10 kbar from 300–350 °C to 450–500 °C; (iii) a pressure decrease at moderate temperatures (～450–500 °C); and (iv) isobaric cooling at ～5–6 kbar from 450–500 to 300 °C. No significant pressure or temperature gap is observed across the upper plate–lower plate discontinuity to the north and west of the Hulw unit. The combination of tectonic and P–T data constrains the stacking chronology of the three main metamorphic units comprising the Saih Hatat window (i.e. the Ruwi‐Quryat, the Hulw‐As Sheikh and the Diqdah‐As Sifah units). These results strengthen the view that the tectonic and metamorphic data are conveniently accounted for by a simple, N‐vergent continental subduction of the passive Arabian margin below the obduction nappe along a cold P–T gradient.     

Fluid transfer of gold,palladium, and rare earth elements and genesis of ore occurrences in the Subpolar Urals

To estimate the behavior of Au, Pd, REE, and Y in magmatic and postmagmatic processes, a series of experimental studies on the solubility of noble metals and REE in magma, magmatic fluid, and hydrothermal solutions has been performed in wide temperature and pressure ranges (300–400°C, 860–1350°C; 1–14 kbar). The coefficients of Au and Pd partitioning (D ^F/L) between fluid and tholeiitic melt have been determined. Depending on P, T, and the composition of the system, they vary from 1 to 11 for Au and 0.02 to 1 for Pd. The phase solubility technique was used to determine Au and Pd solubility in hydrothermal fluid. The effects of temperature, composition, and fluid acidity on Au and Pd solubility have been estimated. The high solubility of these metals in aqueous chloride solutions has been established for both Au (28–803 mg/kg at T = 300°C, 305–1123 mg/kg at T = 350°C, and 330–1400 mg/kg at T = 400°C) and Pd (40–126 mg/kg at T = 300°C, 62–152 mg/kg at T = 350°C, and 20–210 mg/kg at T = 400°C). The coefficients of REE and Y partitioning (D ^F/L) between fluid and tholeiitic or alkaline melts have been determined. They vary from 0.00n to 2 depending on P, T, and fluid composition. The experimental data on Au and Pd solubility in solutions and magmatic fluids and the wide variation of REE D ^F/L between fluid and melt show that magmatic and hydrothermal fluids are efficient agents of Au, Pd, and REE transfer and fractionation. The obtained experimental data were used for elucidating sources of fluids and their role in the genesis of Au-Pd-REE occurrences in the Subpolar Urals.     

Experimental determination of portlandite and brucite solubilities in supercritical H2O

Experimentally reversed portlandite and brucite solubilities were determined between 300° and 600°C and 1 to 3 kbar. In the portlandite runs the molality of Ca decreases with increasing pressure at constant temperature. For instance, at 2 kbar log molalities at 300°, 400°, 500° and 600°C give values of −2.34, −2.71, −3.18 and −4.18, respectively. At 500°C, pressures of 1, 2 and 3 kbar yield values of −4.40, −3.18 and −2.65. Distribution of species in solution can be calculated with the aid of data from Helgeson and co-workers assuming Ca⁺⁺ is the dominant Ca species. These calculated Ca concentrations are within ± 0.2 log units of experimental values in most cases. The solubility reaction is, in all likelihood: 2H⁺ + Ca(OH)₂ ↔a3 Ca⁺⁺ + 2H₂O.Although the computed pH's are close to 2 units greater than neutral, the solutions apparently contained no significant Ca(OH)⁺ or Ca(OH)_2sq.Concentrations of Mg in the brucite runs show a sigmoidal behavior at 2 kbar as a function of temperature with log molalities of Mg of −4.00, −4.28, −4.14 and −4.60 at 350°, 450°, 550° and 600°C, respectively. Values at 1 kbar are lower and decrease monotonically from 350° to 550°C. Based on available thermodynamic data for Mg⁺⁺ it appears that Mg(OH)⁺ is the dominant Mg species in solution. The solubility reaction is proposed to be: H⁺ + Mg(OH)₂↔a3 Mg(OH)⁺ + H₂O.With the aid of data of Helgeson and co-workers values of the equilibrium constant for H₂O + Mg⁺⁺ ↔a3 Mg(OH)⁺ + H⁺ necessary to account for the measured solution compositions can be calculated. These calculations indicate Mg(OH)⁺ becomes dominant at temperatures above 450°C at 2 kbar and above 360°C at 1 kbar at neutral pH.     

On the quantitative evaluation of metamorphic fluid composition: Verification of the results of physicochemical simulations for water-mineral-rock reactions

This paper reports the results of a comparison of the qualitative physicochemical simulations (by the Winsel program complex) of the composition of the reacting fluid with experimental data on the water-electrolyte (NaCl, HCl, NaOH, and KOH)-mineral (quartz, corundum, microcline, and plagioclase) system and the water-electrolyte-rock (granite and pelite) system at 400–800°C and 1–10 kbar. Constraints are proposed for the temperature, pressure, and the composition of the electrolyte at which the simulation results are consistent with the experimental data.     

Fluid evolution of the Hub Stock, Horní Slavkov–Krásno Sn–W ore district, Bohemian Massif, Czech Republic

The Horní Slavkov–Krásno Sn–W ore district is hosted by strongly altered Variscan topaz–albite granite (Krudum granite body) on the northwestern margin of the Bohemian Massif. We studied the fluid inclusions on greisens, ore pockets, and ore veins from the Hub Stock, an apical expression of the Krudum granite. Fluid inclusions record almost continuously the post-magmatic cooling history of the granite body from ～500 to <50°C. Rarely observed highest-temperature (～500°C) highest-salinity (～30?wt.% NaCl eq.) fluid inclusions are probably the result of secondary boiling of fluids exsolved from the crystallizing magma during pressure release which followed hydraulic brecciation of the gneissic mantle above the granite cupola. The greisenization was related to near-critical low-salinity (0–7?wt.% NaCl eq.) aqueous fluids with low amount of CO₂, CH₄, and N₂ (≤10?mol% in total) at temperatures of ～350–400°C and pressures of 300–530 bar. Crush-leach data display highly variable and negatively correlated I/Cl and Br/Cl values which are incompatible with both orthomagmatic and/or metamorphic origin of the fluid phase, but can be explained by infiltration of surficial and/or sedimentary fluids. Low fluid salinity indicates a substantial portion of meteoric waters in the fluid mixture that is in accordance with previous stable isotope data. The post-greisenization fluid activity associated with vein formation and argillitization is characterized by decreasing temperature (<350 to <50°C), decreasing pressure (down to ～50–100 bar), and mostly also decreasing salinity.     

FOREWORD AND TABLE OF CONTENTS OF BOOK "PRINCIPLES OF THE TECTONICS OF CHINA"

An experimental study has been made of the system Pb-Sn-Sb-S and of its sections Pb-Sn-S and PbS-Sb₂S₃ In aqueous solutions of HCl, NH₄Cl and NaOH at T = 300–400°C and total pressure = P_H2O= 1000 atm. All lead and antimony sulfosalts known in nature have been synthesized and also the following sulfostannates: teal lite, franckeite, and cylindrite. The phase relations In a part of the system Pb-Sn-Sb-3 are discussed and an attempt is made to use the experimental data for interpretation of the conditions of deposition of “Bolivian” type ores containing sulfosalts and sulfostannates. —Authors.     

Oxygen isotope fractionation between chlorite and water from 170 to 350°C: a preliminary assessment based on partial exchange and fluid/rock experiments

Oxygen isotope fractionations in laboratory systems have been determined between chlorite and water at 170–350°C. In one series of experiments, the Northrop-Clayton partial exchange method was used where three (sometimes four) isotopically different waters were reacted with chlorite [(∑Fe)/∑Fe+Mg = 0.483] for four durations (132–3282 h) at 350°C and 250 b. The percents of exchange determined for the four times from shortest to longest are 4.4, 6.5, 8.0, and 11.9. The fractionations calculated from the Northrop and Clayton (1966) method are in modest agreement for the four run durations: 0.13, 0.26, −0.46, and −0.55 per mil. Errors associated with each of these fractionations are quite large (e.g., ±1.2 per mil for the longest run). The value determined for the longest run of ∼20 weeks is the most reliable of the group and compares very closely with a value of ∼ −0.7 per mil estimated by Wenner and Taylor (1971) based on natural chlorites. Good agreement is also observed with the estimates, −1.2 and −1.3‰ calculated at 350°C for chlorite compositions with [(∑Fe)/∑Fe+Mg] = 0.313 and 0.444, respectively, from equations given by Savin and Lee (1988) based on their empirical bond-type method.Additional fractionation data have been estimated from hydrothermal granite-fluid experiments where chlorite formed from biotite. Detailed thin section, scanning electron microscope (SEM), x-ray diffraction (XRD), and electron microprobe analyses demonstrate that biotite is altered exclusively to chlorite in 13 granite-fluid experiments conducted at the following conditions: T = 170–300°C, P = vapor saturation − 200 b, salinity = H₂O, 0.1 and 1 m NaCl, fluid/biotite mass ratios = 3−44, run durations = 122−772 h. The amount of chlorite, quantified through point counting and XRD, increased with increasing temperature, salinity, and time. The isotope compositions of chlorite were calculated from mass balance and compared to the final measured δ¹⁸O of the fluids. The 10³ln α values averaged 0.14, 0.8 and 2.9 per mil for 300°, 250°, and 200°C, respectively. A least-squares regression model of the combined data set (all T’s) gives the following expression for fractionation: 1000 ln α_chl-w=2.693 (10⁹/T³)−6.342 (10⁶/T²)+2.969 (10³/T) The curve described by this equation is in very good agreement with empirical curves given by Wenner and Taylor 1971, Savin and Lee 1988 and Zheng (1993).     

Solubility of the buffer assemblage pyrite + pyrrhotite + magnetite in NaCl solutions from 200 to 350°C

In the design of hydrothermal solubility studies it is important that the system be completely defined chemically. If the solubilities of minerals containing m metallic elements are to be determined in hydrothermal NaCl solutions, the phase rule requires that a total of m + 6 independent intensive parameters be controlled or measured in order to determine completely the system.In this study the solubility of the univariant assemblage pyrite + pyrrhotite + magnetite has been determined in vapor saturated hydrothermal solutions from 200 to 350°C for NaCl concentrations ranging from 0.0 to 5.0 molal. At any temperature, oxygen and sulfur fugacities were buffered by the chosen assemblage. System pH was determined from excess CO₂ partial pressures and computed ionic equilibria. Equilibrium constants were calculated by regression analysis of solubility data. The results show that more than 10 ppm of each mineral can dissolve in typical hydrothermal solutions under geologically realistic conditions. Solubilities were best represented by the species Fe²⁺ and FeCl⁺ at 200 and 250°C; Fe²⁺, FeCl⁺ and FeCl₂⁰ at 300°C; and Fe²⁺ and FeCl₂⁰ at 350°C. Ore deposition would occur by lowering temperature, diluting chloride concentration, or by raising pH through wall rock alteration reactions.     

Determination of the first ionization constant of silicic acid from quartz solubility in borate buffer solutions to 350°C

The solubility of quartz has been determined in borax buffer solutions having total boron concentrations of 0.10, 0.20, 0.40 and 0.60 mol kg^?1 and over the temperature range 130–350°C at the saturated vapour pressure of the system. The first ionization constant of silicic acid was calculated from the solubility data and varied from ?logK₁ = 8.88 (± 0.15) at 130°C to ?logK₁ = 10.06 (± 0.20) at 350°C. The solubility of quartz in these solutions was due to the presence of the three species, H₄SiO₄, H₃SiO₄^? and NaH₃SiO₄°. The equilibrium constant for the reaction, Na⁺ + H₃SiO₄^? = NaH₃SiO₄° extended from log K_as = 1.18?1.40 (± 0.20) over the temperature interval 135–301°C. The formation of NaH₃SiO₄° ion pairs was concluded to contribute significantly to the solubility of quartz in alkaline hydrothermal solutions when pH > 8 and sodium concentration exceeds 0.10 mol kg^?1.     

Determination of the HCl dissociation constant at a temperature of 350°C and 200 bars of pressure by the potentiometric method using a ceramic electrode

A technique has been developed for pH measurement in flow-through cells at temperatures from 175 to 350°C and pressures up to 350 bars in a nonisothermal cell consisting of a ZrO₂(Y₂O₃) ceramic electrode and a Ag/AgCl (2 M KCl, 25°C) flow-through reference electrode. This technique has been applied to determination of the HCl dissociation constant at 350°C and 200 bars; previously, the HCl dissociation has not been studied sufficiently reliably under these conditions. The obtained value pK _dis = 2.16 ± 0.03 was used to estimate the acidity of fluids from their chemical composition at the vent of high-temperature submarine hydrothermal solutions.     

Carbonate equilibria in hydrothermal systems: First ionization of carbonic acid in NaCl media to 300°C

The ionization quotients of aqueous carbon dioxide (carbonic acid) have been precisely determined in NaCl media to 5 m and from 50° to 300°C using potentiometric apparatus previously developed at Oak Ridge National Laboratory. The pressure coefficient was also determined to 250°C in the same media. These results have been combined with selected information in the literature and modeled in two ways to arrive at the best fits and to derive the thermodynamic parameters for the ionization reaction, including the equilibrium constant, activity coefficient quotients, and pressure coefficients. The variation with temperature of the two fundamental quantities $\text{Δ}\text{V}\text{?}{}^{\mathrm{o}}$ and $\text{Δ}\text{C}\text{?}{}^{\mathrm{o}}{}_{\mathrm{p}}$ were examined along the saturation vapor pressure curve and at constant density. The results demonstrated again that for reactions with minimal electrostriction changes the magnitudes and variations of $\text{Δ}\text{C}\text{?}{}^{\mathrm{o}}{}_{\mathrm{p}}$ and $\text{Δ}\text{V}\text{?}{}^{\mathrm{o}}$ with temperature are small and, in addition, $\text{Δ}\text{C}\text{?}{}_{\mathrm{p}}$ and $\text{Δ}\text{V}\text{?}$ are approximately independent of salt concentration.The results have also been applied to an examination of the solubility of calcite as a function of pH (in a given NaCl medium) for the neutral to acidic region both for systems with fixed CO₂ pressure and systems where the calcium ion concentration equals the concentration of carbon. The pH of saturated solutions of calcite with P_CO2 of 12 bars increases from 5.1 to 5.5 between 100° and 300°C.     

Recovery of Zn from wastewater of zinc plating industry by precipitation of doped ZnO nanoparticles

In this study, a facile precipitation process to treat wastewater from zinc plating industry is presented. Water purification rates of Zn range between 96.40 % and 99.99 % depending on the reaction conditions. Optimal results are gained at a low pH value of 9, low temperature of 40 °C and a fast alkalization using NaOH solution containing 16 % pure NaOH. Traces of Ni, Fe, Zn, Cu and Cr present in the wastewater were almost completely removed. The precipitates were analysed by X-ray diffraction, infrared and Raman spectroscopy, electron microscopy and magnetic measurements. They consist of doped ZnO as a main phase. Although ZnO exclusively crystallizes in nanoparticle size, the morphology is directly influenced by the experimental parameters. Additionally, very small amounts of ZnCO₃ and Zn(OH)₂ were detected. Magnetic investigations indicate the incorporation of Ni and Fe into the ZnO lattice. The measured saturation magnetization is ~0.01 emu/g and the Curie temperature is ~75 °C.     

Variation of wave velocity and thermal conductivity of concrete after high-temperature treatment

This paper studies the variation of mass, density, wave velocity and thermal conductivity of concrete after high-temperature heat treatment. The range of temperature to which the concrete specimens are exposed is 25–900 °C, in a heating furnace. The results are summarized as follows: three temperature ranges (20–300 °C, 300–600 °C and above 600 °C) corresponding to the moisture vaporization (i.e., adhered water, combined water or crystal water), decomposition of some minerals (i.e., Ca-hydroxide, Mg-hydroxide) and Ca-carbonate are obviously evident. The physical properties of concrete specimens change most significantly within the temperature range above 300 °C, which may be attributed to the transformation of concrete minerals. Moreover, within the temperature range of 300–900 °C, especially between 400 and 600 °C, the concrete structure has significant chemical changes basing on the variations of surface features, ultimately making the number and width of cracks and mass loss level increased, as well as the wave velocity and thermal conductivity changed.     

Behavior of oil in interactions with aqueous solutions under elevated and high temperatures and pressures

The behavior of oil was studied, and the solubility of its light and heavy fractions in hydrothermal solutions was evaluated at 260–700°C and pressures of 30–200 MPa. The experiments were accompanied with simultaneous growth of quartz crystals containing fluid inclusions (in the same solutions). These inclusions allowed one to trace, by means of thermobaric geochemistry, the in situ behavior of oil within a wide range of temperatures and pressures. It was shown that the oil undergoes pronounced transformations under the interactions with hydrothermal solutions. Even at 260–300°C (pressures of 30–50 MPa), the oil was enriched in light fractions. The content of these fractions was pronouncedly increased at 330–350°C (70–80 MPa pressure). This process was accompanied by the appearance of mazut-like, semisolid, and solid bitumoids in amounts that increased manifold within the 400–700°C temperature range (up to 200 MPa pressure). The oil transformations were accompanied by an ample emission of methane. At 260–300°C, the oil in the hydrothermal solution occurred mainly as liquid drops. However, at temperatures near 400°C (about 100–150 MPa pressure), the solubility of light fractions increased to about 5–6 vol % which pointed to the ability to transfer significant amounts of oil not only in the liquid-drop form but also in the dissolved form.     

Experimental determination of the solubility of the assemblage paragonite,albite, and quartz in supercritical H2O

The concentrations of Na, Al, and Si in an aqueous fluid in equilibrium with natural albite, paragonite, and quartz have been measured between 350°C and 500°C and 1 to 2.5 kbar. Si is the dominant solute in solution and is near values reported for quartz solubility in pure H₂O. At 1 kbar the concentrations of Na and Al remain fairly constant from 350°C to 425°C but then decrease at 450°C. At 2 kbar, Na increases slightly with increasing temperature while Al remains nearly constant. Concentrations of Si, Na, and Al all increase with increasing pressure at constant temperature.The molality of Al is close to that of Na and is nearly a log unit greater than calculated molalities assuming Al(OH)⁰₃ is the dominant Al species. This indicates a Na-Al complex is the dominant Al species in solution as shown by Anderson and Burnham (1983) at higher temperature and pressure. The complex can be written as NaAl(OH)⁰₄ ± nSiO₂ where n is the number of Si atoms in the complex. The value of n is not well constrained but appears to be less than or equal to 3.The results indicate Al can be readily transported in pure H₂O solutions at temperatures and pressures as low as 350°C and 1 kbar.     

Estimation of the heat-impact potential for stimulating the development of the deposits of the Bazhenov Formation according to the results of experimental studies

The influence of temperature on rock samples of the Bazhenov Formation is shown. The samples underwent pyrolysis at 300–480°C, as well as in closed autoclaves in the presence of water under formation pressure. The temperature impact at 400°C resulted in a decrease in the S2 pyrolytic peak by 90–95% and almost complete formation of the generation potential of the rocks. Microtomographic studies of samples combined with raster electron microscopy revealed a correlation between the variable reservoir properties of the rocks. At 350°C, the rocks are characterized by a system of fractures; as a result of impacts, the porosity and permeability can increase from several to several tens of times. Our results will allow more precise modeling of the influence of tertiary processes on the rocks of the Bazhenov Formation in order to increase the final oil recovery of the bed.