Standard State Thermodynamic Properties Research Articles

A new activity model for Fe\u2013Mg\u2013Al biotites: II\u2014Applications in the K2O\u2013FeO\u2013MgO\u2013Al2O3\u2013SiO2\u2013H2O (KFMASH) system

The new biotite activity model and standard-state thermodynamic properties of Ann, Phl, and Eas presented in part-I were used to make pseudosections of bulk compositions representing experimental Fe–Mg exchange equilibria and (model) pelitic bulk rock compositions in the system K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH), using mainly the software Perple_X. These pseudosection calculations (termed ‘our calculation(s)’ in the following) were compared to analogous ones performed with the solution model of biotite and thermodynamic data cited in White et al. (J Metamorph Geol 32:261–286, 2014, 10.1111/jmg.12071), termed ‘W14 calculation’. Our calculations with the experimental bulk composition used by Zhou (Ti–Mg–Fe biotites: formation, substitution, and thermodynamic properties at 650 to 900 °C and 1.1 Kb with fO2 defined by the CH4–graphite buffer. PhD thesis, State University of New York, 1994) in his experimental study of the Fe–Mg exchange between biotite (Bt) and olivine (Ol) confirm that biotite had no or only minimal octahedral Al (AlVI) in these experiments. The experimental data of Ferry and Spear (—FS78, Contrib Mineral Petrol 66:113–117, 1978, 10.1007/BF00372150) on the Fe–Mg distribution between biotite and garnet (Grt) are well reproduced by our calculations. The computed composition of biotite (XFe) in equilibrium with garnet of Alm90Py10 composition and the resulting lnKD values as a function of temperature are in good agreement with the experimental brackets. An analogous W14 calculation on the same Fe-rich bulk composition predicts too high XFeBt in order of 0.1 mol fraction. The AlVI contents of biotite of about 0.3–0.45 apfu, as measured by Gessman et al. (Am Mineral 82:1225–1240, 1997, 10.2138/am-1997-11-1218) in similar biotite–garnet exchange experiments performed with Alm80Py20 and Alm70Py30 garnets, are well reproduced by our, as well as by W14 calculations. The extent of Tschermak substitution in biotite in the FS78 experiments, which had Fe-richer bulk compositions, has not been measured. Comparing the FS78 biotites with the ones from Gessman et al. (Am Mineral 82:1225–1240, 1997, 10.2138/am-1997-11-1218), it is very likely that the biotites reported in FS78 contained AlVI in the same order of ca. 0.3–0.4 apfu. A T–XFe (= molar FeO/(FeO + MgO) pseudosection demonstrates the bulk composition dependence of lnKD of the Mg/FeGrt/Bt exchange reaction in high-variance fields. Further comparisons, demonstrating the application of the new biotite solution model in the KFMASH system, are presented in pseudosections constructed for an average model pelite, as well as for a natural high-T/low-P and a natural high-P metapelite. The pseudosections show that biotite according to our biotite model breaks down at lower temperatures and pressures than predicted from the W14 biotite model in the KFMASH system. This means that KFMASH biotite can break down before the wet solidus is reached, which can explain the existence of dry high-T/low-P metapelites. At higher pressures, biotite according to our calculations breaks down at lower pressures than computed with the W14 biotite model. Before biotite breaks down, however, its AlVI content based on our calculations could potentially be used for pseudosection barometry, similarly as the Si-in-phengite barometer. These trends need to be confirmed by a future extension of our model which incorporates Ti, Fe3+ and a di–tri-octahedral substitution.

Thermodynamic Properties of Aqueous Species Calculated Using the HKF Model: How Do Different Thermodynamic and Electrostatic Models for Solvent Water Affect Calculated Aqueous Properties?

Thermodynamic properties of aqueous species are essential for modeling of fluid-rock interaction processes. The Helgeson-Kirkham-Flowers (HKF) model is widely used for calculating standard state thermodynamic properties of ions and complexes over a wide range of temperatures and pressures. To do this, the HKF model requires thermodynamic and electrostatic models of water solvent. In this study, we investigate and quantify the impact of choosing different models for calculating water solvent volumetric and dielectric properties, on the properties of aqueous species calculated using the HKF model. We identify temperature and pressure conditions at which the choice of different models can have a considerable effect on the properties of aqueous species and on fluid mineral equilibrium calculations. The investigated temperature and pressure intervals are 25–1000°C and 1–5 kbar, representative of upper to middle crustal levels, and of interest for modeling ore-forming processes. The thermodynamic and electrostatic models for water solvent considered are: Haar, Gallagher and Kell (1984), Wagner and Pruß (2002), and Zhang and Duan (2005), to calculate water volumetric properties, and Johnson and Norton (1991), Fernandez and others (1997), and Sverjensky and others (2014), to calculate water dielectric properties. We observe only small discrepancies in the calculated standard partial molal properties of aqueous species resulting from using different water thermodynamic models. However, large differences in the properties of charged species can be observed at higher temperatures (above 500°C) as a result of using different electrostatic models. Depending on the aqueous speciation and the reactions that control the chemical composition, the observed differences can vary. The discrepancy between various electrostatic models is attributed to the scarcity of experimental data at high temperatures. These discrepancies restrict the reliability of the geochemical modeling of hydrothermal and ore formation processes, and the retrieval of thermodynamic parameters from experimental data at elevated temperatures and pressures.

Thermodynamic properties of CaCO3–SrCO3–BaCO3 liquids: a molecular dynamics study using new empirical atomic potentials for alkaline earth carbonates

Thermodynamic modeling offers a powerful framework for studying melting reactions of carbonated mantle systems across a wide range of compositions, pressures, and temperatures. Such modeling requires knowledge of the standard state thermodynamic properties of the pure alkaline earth carbonate liquid components, which are difficult to determine experimentally due to their instability at 1 bar. Atomistic simulations offer a solution to these experimental difficulties by providing access to metastable states and supplying constraints on thermodynamic properties. We developed an empirically-derived potential model for the simulation of alkaline earth carbonates (MgCO3, CaCO3, SrCO3 and BaCO3), emphasizing the accurate simulation of the standard state thermodynamic properties of carbonate liquids. Molecular dynamics (MD) simulations of liquids in the CaCO3–SrCO3–BaCO3 system are performed over a geologically relevant temperature–pressure range (1100–3400 K and 0–43 GPa). Simulation data for each of these three components (up to a maximum of 2300 K and 30 GPa) are fitted to a temperature-dependent third-order Birch–Murnaghan equation-of-state to estimate their standard state thermodynamic properties. With a few exceptions, calculated properties agree well with available estimates from experiments and/or first-principles MD simulations. Exploration of binary mixtures supports ideal mixing of volumes, heat capacities, and compressibilities, reflecting the common liquid structure and pressure–temperature evolution for these three components. The success of this new model for CaCO3–SrCO3–BaCO3 liquids suggests that it can accurately predict the properties of MgCO3-bearing liquids, where experimental data are unavailable.

Experimental determination of the solubility product of dolomite at 50–253 °C

The ‘dolomite problem’, the scarcity of present-day dolomite formation near the Earth’s surface, has attracted much attention over the past century. Solving this problem requires having reliable data on the stability and kinetics of formation of this mineral. Toward this goal, the solubility of natural dolomite (CaMg(CO3)2) has been measured from 50 to 253 °C in 0.1 mol/kg NaCl solutions using a hydrogen electrode concentration cell (HECC). The obtained apparent solubility products (Kapp-sp-dol), for the reaction: CaMg(CO3)2 = Ca2+ + Mg2+ + 2CO32−, were extrapolated to infinite dilution to generate the solubility product constants for this reaction (Ksp°-dol). The derived equilibrium constants were fit and can be accurately described by log10Ksp°-dol = a + b/T (K) + cT (K) where a = 17.502, b = −4220.119 and c = −0.0689. This equation and its first and second derivatives with respect to T were used together with corresponding aqueous species properties to calculate the revised standard state thermodynamic properties of dolomite at 25 °C and 1 bar, yielding a Gibbs energy of formation (ΔfG298.15∘) equal to −2160.9 ± 2 kJ/mol, (log10Ksp°-dol = −17.19 ± 0.3); an enthalpy of formation (ΔfH298.15∘) of −2323.1 ± 2 kJ/mol, an entropy (S298.15∘) of 156.9 ± 2 J/mol/K and heat capacity (Cp298.15∘) of 154.2 ± 2 J/mol/K (uncertainties are 3σ). The dolomite solubility product derived in this study is nearly identical to that computed using SUPCRT92 (Johnson et al., 1992) at 200 °C, but about one order of magnitude higher at 50 and 25 °C, suggesting that dolomite may be somewhat less stable than previously assumed at ambient temperatures.

Implications of sepiolite dehydration for earthquake nucleation in the Galera Fault Zone: A thermodynamic approach

A new thermodynamic model for the Mg-phyllosilicate sepiolite was developed and used to calculate its P-T stability conditions and water content for different bulk rock compositions. The standard-state thermodynamic properties, entropy (S°) and enthalpy (H°), were initially estimated by oxide summation taking into account the different entropic and enthalpic contributions of the three types of water in sepiolite: zeolitic water, bound water, and structural OH groups. The starting model was then refined with experimental data. The dehydration process follows a step function that allowed us to define “end-members” with decreasing hydration states in a theoretical solid solution.The stability field of sepiolite is ultimately limited by the reaction sepiolite = talc + quartz + H2O, which is located at about 325 °C at 1–500 MPa. The large thermodynamic stability field of this clay mineral suggests that it could control the mechanical behaviour of crustal faults to 325 °C. The refined model was then applied to the natural case of the Galera Fault Zone (SE Spain) using thermogravimetric analysis and X-ray fluorescence data of the bulk rock composition of the fault core gouge, which is mainly composed of sepiolite. The dehydration of sepiolite at T < 300 °C is modest compared to that occurring during its breakdown, where 62% of water molecules leave the structure to form the association talc + quartz + H2O; a reaction that also involves a reduction of around 31% of the original solid volume. These significant hydration and volume changes of sepiolite can have important implications on the strength and mechanical stability of the Galera Fault and other sepiolite-bearing gouges. We compare triaxial friction experiments on the natural sepiolite-rich gouge with a synthetic gouge to estimate strength changes on the gouge with depth. The synthetic gouge represents the breakdown association above 325 °C, and was constructed following the mineral phases predicted by the thermodynamic model (93 wt% talc and 7 wt% quartz). The contrasting frictional strength and mechanical stability of sepiolite in comparison to talc could be one of the causes of fault instability and earthquake nucleation seen to be concentrated in the upper 13 km of the Galera Fault.

Thermodynamic analysis of hydrothermal synthesis of nanoparticles

The hydrothermal method is one of the most commonly employed techniques for synthesis of metal oxides, metals, and metal composites with different crystalline structures and morphologies, that are in the form of fine particles. The hydrothermal synthesis of nanoparticles involves hydrolysis of metal salt and condensation of metal hydroxide to produce ultrafine metal or metal oxide particles. We propose a Thermodynamic Modeling Framework for predicting the stability of the chemical species under the hydrothermal conditions. This can help in identifying the feasible regions for the hydrothermal synthesis of materials. The method is based on the integration of the Gibbs free energy equation, modified Bromley model for predicting activity coefficients, and the revised Helgeson-Kirkham-Flowers (HKF) model for estimating the standard-state thermodynamic properties of the species. The framework is tested with published experimental data for the synthesis of boehmite under subcritical temperature and supercritical conditions. The stability diagrams are generated for ceria and boehmite. The effect of pressure on the stability of the ceria species is studied. The proposed thermodynamic framework is useful for determining and identifying the process conditions under which the metal complex of interest is thermodynamically stable.

A Systematic Investigation of the Thermodynamic Properties of Aqueous Barium Sulfate up to High Temperatures and High Pressures

Standard state thermodynamic properties for completely dissociated aqueous barium sulfate, BaSO4(aq), were fixed by an ionic additivity relationship using the data from other completely dissociated electrolytes, barium chloride, sodium sulfate, and sodium chloride, from 298.15 to 598.15 K and at steam saturated pressure, psat. The solubility of barium sulfate in pure water was then predicted a priori from 273.15 to 598.15 K and pressures up to 140 MPa, and the results were compared with the literature data. These predicted solubility values for barium sulfate in pure water, when corrected for ion pair association of Ba2+(aq) ion with SO42–(aq) ion and hydrolysis of SO42–(aq) ion, are in very good agreement with the literature data to well within the uncertainties of the experimental data at all temperatures and pressures considered. Using the experimental data from this study and auxiliary data from the literature, the logarithm of the molar dissociation constants of BaSO4° associated ion pair were also c...

Geobiochemistry of metabolism: Standard state thermodynamic properties of the citric acid cycle

Integrating microbial metabolism into geochemical modeling allows assessments of energy and mass transfer between the geosphere and the microbial biosphere. Energy and power supplies and demands can be assessed from analytical geochemical data given thermodynamic data for compounds involved in catabolism and anabolism. Results are reported here from a critique of the available standard state thermodynamic data for organic acids and acid anions involved in the citric acid cycle (also known as the tricarboxylic acid cycle or the Krebs cycle). The development of methods for estimating standard state data unavailable from experiments is described, together with methods to predict corresponding values at elevated temperatures and pressures using the revised Helgeson–Kirkham–Flowers (HKF) equation of state for aqueous species. Internal consistency is maintained with standard state thermodynamic data for organic and inorganic aqueous species commonly used in geochemical modeling efforts. Standard state data and revised-HKF parameters are used to predict equilibrium dissociation constants for the organic acids in the citric acid cycle, and to assess standard Gibbs energies of reactions for each step in the cycle at elevated temperatures and pressures. The results presented here can be used with analytical data from natural and experimental systems to assess the energy and power demands of microorganisms throughout the habitable ranges of pressure and temperature, and to assess the consequences of abiotic organic compound alteration processes at conditions of subsurface aquifers, sedimentary basins, hydrothermal systems, meteorite parent bodies, and ocean worlds throughout the solar system.

Melting relations in the system FeCO3–MgCO3 and thermodynamic modelling of Fe–Mg carbonate melts

To constrain the thermodynamics and melting relations of the siderite–magnesite (FeCO3–MgCO3) system, 27 piston cylinder experiments were conducted at 3.5 GPa and 1170–1575 °C. Fe-rich compositions were also investigated with 13 multi-anvil experiments at 10, 13.6 and 20 GPa, 1500–1890 °C. At 3.5 GPa, the solid solution siderite–magnesite coexists with melt over a compositional range of X Mg (=Mg/(Mg + Fetot)) = 0.38–1.0, while at ≥10 GPa solid solution appears to be complete. At 3.5 GPa, the system is pseudo-binary because of the limited stability of siderite or liquid FeCO3, Fe-rich carbonates decomposing at subsolidus conditions to magnetite–magnesioferrite solid solution, graphite and CO2. Similar reactions also occur with liquid FeCO3 resulting in melt species with ferric iron components, but the decomposition of the liquid decreases in importance with pressure. At 3.5 GPa, the metastable melting temperature of pure siderite is located at 1264 °C, whereas pure magnesite melts at 1629 °C. The melting loop is non-ideal on the Fe side where the dissociation reaction resulting in Fe3+ in the melt depresses melting temperatures and causes a minimum. Over the pressure range of 3.5–20 GPa, this minimum is 20–35 °C lower than the (metastable) siderite melting temperature. By merging all present and previous experimental data, standard state (298.15 K, 1 bar) thermodynamic properties of the magnesite melt (MgCO3L) end member are calculated and the properties of (Fe,Mg)CO3 melt fit by a regular solution model with an interaction parameter of −7600 J/mol. The solution model reproduces the asymmetric melting loop and predicts the thermal minimum at 1240 °C near the siderite side at X Mg = 0.2 (3.5 GPa). The solution model is applicable to pressures reaching to the bottom of the upper mantle and allows calculation of phase relations in the FeO–MgO–O2–C system.

SUPCRTBL: A revised and extended thermodynamic dataset and software package of SUPCRT92

The computer-enabled thermodynamic database associated with SUPCRT92 (Johnson et al., 1992) enables the calculation of the standard molal thermodynamic properties of minerals, gases, aqueous species, and reactions for a wide range of temperatures and pressures. However, new data on the thermodynamic properties of both aqueous species and minerals have become available since the database’s initial release in 1992 and its subsequent updates. In light of these developments, we have expanded SUPCRT92’s thermodynamic dataset and have modified the accompanying computer code for thermodynamic calculations by using newly available properties. The modifications in our new version include: (1) updating the standard state thermodynamic properties for mineral end-members with properties from Holland and Powell (2011) to improve the study of metamorphic petrology and economic geology; (2) adding As-acid, As-metal aqueous species, and As-bearing minerals to improve the study of environmental geology; (3) updating properties for Al-bearing species, SiO2°(aq) and HSiO3-, boehmite, gibbsite, and dawsonite for modeling geological carbon sequestration. The new thermodynamic dataset and the modified SUPCRT92 program were implemented in a software package called SUPCRTBL, which is available online at www.indiana.edu/~hydrogeo/supcrtbl.html.

Dissociation Constant (pKa) and Thermodynamic Properties of Some Tertiary and Cyclic Amines from (298 to 333) K

The potentiometric titration method was used to measure pKa values of nine amines [2-(diisopropylamino)ethanol [2-DIPA], N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine [THPEDA], 2-{[2-(dimethylamino) ethyl]methyl amino} ethanol [2-DMAEMAE], tris[2-(2-methoxyethoxy)ethyl]amine [TMEEA], N-(2-hydroxyethyl) aniline [2-HEAN], 1-(2-hydroxyethyl)piperazine [HEP], piperazine [PZ], monoethanolamine [MEA], and N-methyldiethanolamine [MDEA] at (298.15, 303.15, 313.15, 323.15, and 333.15) K. pKa values of the last three amines were compared with published data to validate the procedure and assess the accuracy of the instrument. Thermodynamic quantities, such as standard enthalpy (ΔH°·kJ–1·mol–1) and entropy (ΔSo·kJ–1·mol–1) for the dissociation process, were determined at 298.15 K using the van’t Hoff equation. From the experimental results, the values of the standard state thermodynamic properties were derived and compared to the values of commercially available amines used as absorbents for CO2 capture. Among t...

Dissociation Constants (pKa) of Tertiary and Cyclic Amines: Structural and Temperature Dependences

The dissociation constants of the conjugate acids of 14 amines (diethylethanolamine, monoethanolamine, n-butyldiethanolamine, t-butyldiethanolamine, n,n-dimethylpropanolamine, methyl-diethanolamine, ethyldiethanolamine, monoethylethanolamine, n,n-dimethylisopropanolamine, triethanolamine, 4-methylpiperazine-1-amine, 3-morpholino propylamine, 4,2-hydroxylethylmorpholine, and triethylamine) were measured over a temperature range between 293.15 and 333.15 K using the potentiometric titration method. The change in standard state thermodynamic properties was derived from the van’t Hoff equation. The influence of the steric hindrance, number of −OH groups, and length of alkyl chain on the dissociation constants was identified. Of the studied amines, few sterically hindered derivatives of piperazine, a secondary amine monoethylethanolamine, and a tertiary amine n,n-dimethylpropanolamine have high pKa values but lower standard enthalpy than those of the benchmark amine, monoethanolamine (MEA), and thus were deemed promising for CO2 capture technology. Monoethylethanolamine (MEEA) was found to have the highest basicity (pKa) with the lowest standard state enthalpy (ΔH°/kJ·mol–1).

A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO–FeO–Al2O3–SiO2–H2O: applications to P–T sections and geothermometry

We present a new thermodynamic activity-composition model for di-trioctahedral chlorite in the system FeO–MgO–Al2O3–SiO2–H2O that is based on the Holland–Powell internally consistent thermodynamic data set. The model is formulated in terms of four linearly independent end-members, which are amesite, clinochlore, daphnite and sudoite. These account for the most important crystal-chemical substitutions in chlorite, the Fe–Mg, Tschermak and di-trioctahedral substitution. The ideal part of end-member activities is modeled with a mixing-on-site formalism, and non-ideality is described by a macroscopic symmetric (regular) formalism. The symmetric interaction parameters were calibrated using a set of 271 published chlorite analyses for which robust independent temperature estimates are available. In addition, adjustment of the standard state thermodynamic properties of sudoite was required to accurately reproduce experimental brackets involving sudoite. This new model was tested by calculating representative P–T sections for metasediments at low temperatures (<400 °C), in particular sudoite and chlorite bearing metapelites from Crete. Comparison between the calculated mineral assemblages and field data shows that the new model is able to predict the coexistence of chlorite and sudoite at low metamorphic temperatures. The predicted lower limit of the chloritoid stability field is also in better agreement with petrological observations. For practical applications to metamorphic and hydrothermal environments, two new semi-empirical chlorite geothermometers named Chl(1) and Chl(2) were calibrated based on the chlorite + quartz + water equilibrium (2 clinochlore + 3 sudoite = 4 amesite + 4 H2O + 7 quartz). The Chl(1) thermometer requires knowledge of the (Fe3+/ΣFe) ratio in chlorite and predicts correct temperatures for a range of redox conditions. The Chl(2) geothermometer which assumes that all iron in chlorite is ferrous has been applied to partially recrystallized detrital chlorite from the Zone houillère in the French Western Alps.

The effect of aqueous alcohols (methanol, t-butanol) and sulfolane on the dissociation constants and thermodynamic properties of alkanolamines

The dissociation constants of protonated monoethanolamine, N-methyldiethanolamine have been determined in aqueous mixtures of methanol, t-butanol–water and sulfolane solvents. The mole fractions of the organic compounds ranged from (0.2 to 0.95) and the temperatures from (283 to 353)K. Standard state thermodynamic properties like ΔrG, were derived from the results. The basic strength of the protonated alkanolamine decreased with decreasing dielectric constant and increase in temperature of the solvent.

A Priori Prediction of Thermodynamic Properties of Electrolytes in Mixed Aqueous–Organic Solvents to Extreme Temperatures

The unified theory of electrolytes (J. Phys. Chem. B 2009, 113, 2398-2404) for predicting the standard state thermodynamic properties of aqueous electrolytes has been extended to include mixed solvent systems. The solubility of solid sodium chloride in mixed solvents (methanol/water concentration up to 75% w/w) was also measured up to 466 K and pressures near 7 MPa. The present model, together with a simple modification of Pitzer's thermodynamic treatment of aqueous solutions, allows a priori prediction of solubility of electrolytes in aqueous/organic systems to extreme temperatures and pressures. Solubility is predicted for sodium chloride and potassium chloride in mixed solvents (methanol/water, ethanol/water) over a wide range of temperatures and compositions from the extension of the unified theory of electrolytes to mixed solvents. Comparisons indicate good agreement in all cases to well within the uncertainties of the experimental data. The stoichiometric activity coefficients of saturated solution of sodium chloride in methanol/water mixed solvents were calculated up to 473.15 K. The stoichiometric activity coefficients, as a function of temperature at all concentrations (0 ≤ m ≤ m(sat)) and the entire range of mole fraction of methanol, were also calculated up to 473.15 K. The novelty of the present approach is that no additional parameters are required to account for the medium effect.

Hydration thermodynamics of the SWy-1 montmorillonite saturated with alkali and alkaline-earth cations: A predictive model

The aim of the present work was to study the thermodynamic equilibria between water and a homo-ionic montmorillonite SWy-1 saturated by different cations. The choice of this smectite is justified by the large set of experimental data available from the literature for eight different interlayer cations: Na +, K +, Rb +, Cs +, Mg 2+, Ca 2+, Sr 2+, and Ba 2+. In particular, studies by Cases et al. (1992, 1997) and Bérend et al. (1995) are providing heat of adsorption data, pairs of desorption–adsorption isotherms, and information about the partition of adsorption–desorption water molecules between external surfaces and internal spaces. By calculating the effective amount of hydration water as the difference between the so-called gravimetric water and the surface covering water, a thermodynamic model was then developed, based on the concept of Ransom and Helgeson (1994) considering an asymmetric subregular binary solid solution between a fully hydrated and a anhydrous smectite. A set of six thermodynamic parameters ( Δ H ∘ hyd , S ∘ hyd and four Margules parameters) was extracted by a least square method from measurements of enthalpies of adsorption and paired adsorption–desorption isotherms for each interlayer cation. These six initial parameters were then used to determine a complete set of standard thermodynamic hydration parameters ( Δ H ∘ hyd , Δ G ∘ hyd , Δ S ∘ hyd , heat capacity, molar volume, and number of interlayer H 2O) and quantify, for each cation, the number of moles of hydration water molecules as a function of relative humidity and temperature. The validation of the standard state thermodynamic properties of hydration for each end member was carried out using three approaches: (1) a comparison with experimental isotherms obtained on hetero-ionic and homo-ionic SWy-1 smectite at different temperatures; (2) a comparison with the experimental integral enthalpy and entropy of hydration of the SWy-1 smectite; and (3) a comparison with experimental isotherms acquired on various smectites (Upton, MX80, Arizona) with different layer charges. Eventually, the present work demonstrates that, from a limited number of measurements, it is possible to provide the hydration thermodynamic parameters for hydrated smectites with different compositions and under different conditions of temperature and relative humidity, using the newly developed predictive model.

Real-solution stability diagrams for copper-ammonia-chloride-water system

A comprehensive thermodynamic model, which combined the Helgeson-Kirkham-Flowers (HKF) equation of state for standard-state thermodynamic properties of all species with realistic activity coefficient model developed by BROMLEY, was used to calculate the thermodynamic equilibrium, and a graphical method was developed to construct predominance existence diagrams (PED) for copper-ammonia-chloride in the presence of realistically modeled aqueous solutions. The existence of the different predominant chemical species for Cu(II) predicted by the diagrams was corroborated by spectrophotometrical studies and X-ray diffractometry. The simulated and experimental results indicate that the predominance of a given species in solution strongly depends on the pH value in this system. More quantitative information on real copper hydrometallurgy in the presence of ammonia and chloride can be obtained from these diagrams compared with the conventional predominance existence diagrams.

Ab-initio assessment of conventional standard-state thermodynamic properties of geochemically relevant gaseous and aqueous species

After some introductory remarks on the essential basic concepts concerning isolated (gas state) atoms and molecules (adiabatic vs. vertical ionization potential and electron affinity; dissociation energy), we will show how their (absolute) internal energy and enthalpy (i.e. “thermal corrections” to the energy of the molecule) may be converted into the conventional counterparts of common use in thermochemistry through an appropriate thermochemical cycle. The first-principles acceptation of entropy, in terms of translational, rotational, vibrational, and electronic contributions to the bulk partition function, will then be briefly restated, emphasizing that, for practical calculations, the V-dependency of the translational terms can be converted into a P-dependency with the perfect gas law. The entropy of “aqueous” species will then be discussed after some preliminary remarks on the significance of the “solvation entropy” in terms of a Polarized Continuum Model (PCM) conceptual framework, and some comments on the energy of the “hydronium ion” H 3O +. Some comments on the nature of the electrostatic portion of the solvation entropy, in terms of the Born solvation theory, and the non-electrostatic portion (solvent collapse+cavity formation+dispersion+repulsion+liberation entropy terms), will then be made, showing how this last term may be computed practically by exploiting its analogy with the Helgeson–Kirkham–Flowers electrostatic approach. After some elementary application of the various concepts to the gaseous state, we will present a potential application of major use in geochemistry, i.e. the possibility of computing ab-initio the interaction parameters (i.e. individual activity coefficients) of complex ions in solution through PCM procedures. We will then discuss the state of the art attained in determining ab-initio the p K a scale of organic and inorganic acids, perhaps the most demanding task, due to the high level of internal precision required. Finally, we will give some examples of the application of the assessment of the Gibbs free energy of formation from the elements ( G f °), the enthalpy of formation from the elements ( H f °), and entropy ( S°) at standard state (hypothetical 1-molal solution referred to infinite dilution at 298.15 K and 10 5 Pa) on geochemically relevant aqueous species of heavy metals.

Thermodynamic Properties of Aqueous Polyatomic Ions at Extreme Temperatures and Pressures

Recently a theoretical treatment (J. Phys. Chem. B 2009, 113, 2398-2404) was developed for predicting the standard state thermodynamic properties of electrolytes up to and beyond the critical temperature of water (1273 K and at pressures up to 1000 MPa). In general, the model requires sufficient data at 298.15 K including the Gibbs free energy of hydration and at two higher temperatures to fix two constants for each electrolyte. This communication describes an extension of this "two constant" theory to thermodynamic properties of polyatomic ions for which no accurate data for the Gibbs free energy of hydration exits at 298.15 K.

The effect of aqueous organic solvents on the dissociation constants and thermodynamic properties of alkanolamines

The dissociation constants of protonated monoethanolamine and N-methyldiethanolamine have been determined in methanol–water, ethanol–water, and t-butanol–water solvents. The alcohol mole fractions were ranging from 0.2 to 0.95 and the temperatures from 283 to 323 K, 283 to 333 K, and at 298.15 K, respective to the different solvents. The experimental results are reported with the standard state thermodynamic properties. The basic strength of the protonated alkanolamine decreases with decreasing dielectric constant and increasing temperature of the solvent. By using the dissociation constants of the alkanolamines in pure water, it is shown that a Born treatment alone is not able to estimate the dissociation constants when the composition of the solvent is changed to an aqueous organic mixture.