Christomir Christov

Thermodynamics of the aqueous sodium and magnesium bromide system at the temperatures 273.15 K and 298.15 K

A thermodynamic approach based on the Pitzer model has been used for plotting the theoretical solubility isotherms of the NaBr-MgBr2-H2O system at the temperatures T = 273.15 K and T = 298.15 K. The thermodynamic functions (osmotic coefficients, binary parameters of interionic interaction and thermodynamic solubility products) needed for simulation at T = 273.15 K of the corresponding binary solutions have been calculated using empirical approximating equations which express the dependence of osmotic coefficients and binary parameters on temperature. The ternary Pitzer parameters are calculated using experimental data on the solubility of the saturated ternary solution. Good agreement Between experimental and calculated solubilities has been found.

Thermodynamic simulation of four-component carnallite type systems

SummaryThe standard method ofPitzer for predicting the solubility isotherms of systems in which solid phases with a constant composition crystallize is applied to cases when mixed crystals are formed. The four-component carnallite type systems RbCl-CsCl-MgCl2-H2O, RbCl-KCl-MgCl2-H2O, and RbCl-RbBr-MgCl2-MgBr2-H2O and the corresponding subsystems are thermodynamically simulated at 25°C. It is established that the solubility diagrams consist of crystallization regions of the simple saltsMX,M′X′, MgX2·6H2O, and MgX′2·6H2O and of the corresponding carnallite type double salts with the composition 1:1:6. A method of calculation of the integralGibbs energy of mixingGmix(s) of crystals formed in water-salt systems has been proposed. The results on the systems RbCl-KCl-H2O, RbCl-RbBr-H2O, and MgCl2-MgBr2-H2O are compared with experimental data from the literature and with values calculated using various models.ZusammenfassungDiePitzer-Methode zur Voraussage der Löslichkeitsisothermen in Mehrstoffsystemen, in welchen feste Phasen mit konstanter Zusammensetzung auskristallisieren, wurde auch für Fälle angewendet, bei denen sich Mischkristalle bilden. Die Vierstoffsysteme RbCl-CsCl-MgCl2-H2O, RbCl-KCl-MgCl2-H2O und RbCl-RbBr-MgCl2-MgBr2-H2O, aus welchen Carnallit-Typ-Mischkristalle auskristallisieren, und die dazugehörigen Dreistoff-Randsysteme wurden bei 25°C simuliert. Man stellt fest, daß die Löslichkeitsdiagramme sowohl Kristallisationsbereiche der einfachen SalzeMX,MX, MgX2·6H2O und MgX′2·6H2O als auch der entsprechenden carnallitartigen Doppelsalze mit der Zuzammensetzung 1:1:6 umfassen. Eine Methode zur Berechnung derGibbs-EnergieGmix(s) für die in Wasser-Salz-Systemen gebildeten Mischkristalle wird vorgeschlagen. Die für die Systeme RbCl-KCl-H2O, RbCl-RbBr-H2O und MgCl2-MgBr2-H2O erhaltenen Ergebnisse werden mit experimentellen Literaturdaten und Resultaten von Berechnungen aufgrund verschiedener Modelle verglichen.

Thermodynamic study of the NaCl Na2SO4 Na2Cr2O7 H2O system at the temperature 298.15 K

Abstract The Pitzer ion-interaction model has been used for thermodynamic simulation of the ternary NaClue5f8Na 2 Cr 2 O 7 ue5f8H 2 O and Na 2 SO 4 ue5f8Na 2 Cr 2 O 7 ue5f8H 2 O, and the quaternary NaClue5f8Na 2 ue5f8SO 4 -Na 2 Cr 2 O 7 -H 2 O systems at T=298.15 K. The necessary thermodynamic functions (binary and ternary parameters of interionic interaction and thermodynamic solubility products) have been calculated and the theoretical solubility isotherms have been plotted. Good agreement between experimentally determined and calculated solubilites has been found.

Thermodynamical study on the magnesium selenate-nickel selenate-water system at 25°C

SummaryActivity coefficients of the salt components in both the saturated solutions and the (MgxNi1−x)SeO4·6H2O mixed crystals of the MgSeO4-NiSeO4-H2O system at 25°C have been determined by the isopiestic method. It has been established that the formed mixed crystals deviate only slightly from ideality and can be adequately described by a regular model. ThePitzer ion-interaction model has been used to calculate the thermodynamic properties of the salt components in the ternary system. The calculated data are in good agreement with those obtained experimentally by the isopiestic method.ZusammenfassungDie Aktivitätskoeffizienten der Salzkomponenten sowohl der gesättigten Lösungen als auch der Mischkristalle (Zusammensetzung: (MgxNi1−x)SeO4·6H2O) des Systems MgSeO4-NiSeO4-H2O wurden bei 25°C mit Hilfe der isopiestischen Methode bestimmt. Es konnte gezeigt werden, daß die gebildeten Mischkristalle nur leicht vom idealen Zustand abweichen und mit einem regulären Modell gut beschrieben werden können. Zur Berechnung der thermodynamischen Eigenschaften der Salzkomponenten des ternären Systems wurde dasPitzersche lonenwechselwirkungsmodell herangezogen. Die berechneten Werte stimmen mit den mittels der isopiestischen Methode gewonnenen experimentellen Ergebnissen gut überein.

A thermodynamic model of aqueous electrolyte solution behavior and solid-liquid equilibrium in the Li-H-Na-K-Cl-OH-H2O system to very high concentrations (40 molal) and from 0 to 250 °C

This paper describes a chemical model that calculates solute and solvent activities and solid-liquid equilibria in the Li-H-Na-K-Cl-OH-H2O system from dilute to high solution concentration within the 0 to 250 °C temperature range. The model coherently extends to Li the temperature-variable H-Na-K-OH-Cl-H2O model of Christov and Møller (2004b, p. 1309). The solubility modeling approach based on Pitzers (1973, p. 268) specific interaction equations is used. All binary (LiCl-H2O and LiOH-H2O) and ternary (LiCl-HCl-H2O, LiCl-NaCl-H2O, LiCl-KCl-H2O, LiOH-NaOH-H2O, LiOH-KOH-H2O, and LiOH-LiCl-H2O) lithium subsystems are included in the model parameterization. The model for the LiCl-H2O system is parameterized using two different approaches: (1) with 4 ion interaction binary parameters (β(0), β(1), β(2), and Cϕ), and (2) with 3 ion interaction binary parameters (β(0), β(1), and Cϕ) and including neutral aqueous LiCl0(aq) species. Approach (2) provides a better fit of activity data in unsaturated binary solutions and accurately predicts solid solubilities up to 40 mol.kg−1 and up to 250 °C. Therefore, this approach was used to parameterize lithium chloride mixed systems. Temperature functions for the thermodynamic solubility product (as log Kosp) of 5 simple lithium salts (LiCl.2H2O(cr), LiCl. H2O(cr), LiCl(cr), LiOH. H2O(cr), and LiOH(cr)) are determined. The log Kosp values of 3 double lithium basic salts precipitating in the LiOH-LiCl-H2O system at 50 °C (3LiOH.LiCl(cr), LiOH.LiCl(cr), and LiOH.3LiCl(cr)) are also estimated using solubility data.

Thermodynamic Study on Aqueous Solutionsof (NH4)2SeO4 and K2SeO4 at 298.15 K

Summary.u2002The isopiestic method has been used to determine the osmotic coefficients of binary solutions of (NH4)2SeO4 (from 2.739 to 5.502u2009molċkg−1) and K2SeO4 (from 1.086 to 4.742u2009molċkg−1) in H2O at 298.15u2009K. The Pitzer ion-interaction model has been employed for the thermodynamic analysis of the results. The optimum values of the binary parameters of ionic interaction have been calculated, and important thermodynamic characteristics of (NH4)2SeO4 and K2SeO4 have been determined.Zusammenfassung.u2002Die isopiestische Methode wurde zur Bestimmung der osmotischen Koeffizienten binaürer Loüsungen von (NH4)2SeO4 (2.739–5.502u2009molċkg−1) und K2SeO4 (1.086–4.742u2009molċkg−1) in H2O bei 298.15u2009K benutzt. Die Ergebnisse wurden mit Hilfe des Pitzer-Modells thermodynamisch analysiert. Optimale Werte der binaüren Parameter der interionischen Wechselwirkung wurden berechnet, und wichtige thermodynamische Charakteristiken von (NH4)2SeO4 und K2SeO4 wurden bestimmt.

Investigation of the Aqueous Lithium and Nickel Selenate System

The isopiestic method has been used to determine the water activity in the binary solutions Li2Se04-H20 at 25°C. The solubilities in the system Li2Se04-NiSe04-H20 have been investigated by the physicochemical analysis method. It has been established that the system is of a simple eufonie type. The Pitzer ion-interaction model has been used for thermodynamic analysis of the results obtained. The thermodynamic functions needed (binary and ternary parameters of interionic interaction, thermodynamic solubility products) have been calculated and the theoretical solubility isotherm has been plotted. The experimentally obtained and the calculated solubilities are in very good agreement, which proves the correctness of the experimental results obtained.

Thermodynamic model for solution behavior and solid-liquid equilibrium in Na-Al(III)-Fe(III)-Cr(III)-Cl-H2O system at 25°C

Abstract The knowledge of the thermodynamic behavior of multicomponent aqueous electrolyte systems is of main interest in geo-, and environmental-sciences. The main objective of this study is the development of a high accuracy thermodynamic model for solution behavior, and highly soluble M(III)Cl3(s) (M= Al, Fe, Cr) minerals solubility in Na-Al(III)-Cr(III)-Fe(III)-Cl-H2O system at 25°C. Comprehensive thermodynamic models that accurately predict aluminium, chromium and iron aqueous chemistry and M(III) mineral solubilities as a function of pH, solution composition and concentration are critical for understanding many important geochemical and environmental processes involving these metals (e.g., mineral dissolution/alteration, rock formation, changes in rock permeability and fluid flow, soil formation, mass transport, toxic M(III) remediation). Such a model would also have many industrial applications (e.g., aluminium, chromium and iron production, and their corrosion, solve scaling problems in geothermal energy and oil production). Comparisons of solubility and activity calculations with the experimental data in binary and ternary systems indicate that model predictions are within the uncertainty of the data. Limitations of the model due to data insufficiencies are discussed. The solubility modeling approach, implemented to the Pitzer specific interaction equations is employed. The resulting parameterization was developed for the geochemical Pitzer formalism based PHREEQC database.

Thermodynamic Study on Aqueous Solutionsof (NH4)2SeO4 and K2SeO4 at 298.15 K@@@Thermodynamische Untersuchungen an wäßrigen Lösungen von (NH4)2SeO4 und K2SeO4 bei 298.15 K

Summary.u2002The isopiestic method has been used to determine the osmotic coefficients of binary solutions of (NH4)2SeO4 (from 2.739 to 5.502u2009molċkg−1) and K2SeO4 (from 1.086 to 4.742u2009molċkg−1) in H2O at 298.15u2009K. The Pitzer ion-interaction model has been employed for the thermodynamic analysis of the results. The optimum values of the binary parameters of ionic interaction have been calculated, and important thermodynamic characteristics of (NH4)2SeO4 and K2SeO4 have been determined.Zusammenfassung.u2002Die isopiestische Methode wurde zur Bestimmung der osmotischen Koeffizienten binaürer Loüsungen von (NH4)2SeO4 (2.739–5.502u2009molċkg−1) und K2SeO4 (1.086–4.742u2009molċkg−1) in H2O bei 298.15u2009K benutzt. Die Ergebnisse wurden mit Hilfe des Pitzer-Modells thermodynamisch analysiert. Optimale Werte der binaüren Parameter der interionischen Wechselwirkung wurden berechnet, und wichtige thermodynamische Charakteristiken von (NH4)2SeO4 und K2SeO4 wurden bestimmt.

Thermodynamic Study on Aqueous Solutionsof (NH 4 ) 2 SeO 4 and K 2 SeO 4 at 298.15 K

Summary.u2002The isopiestic method has been used to determine the osmotic coefficients of binary solutions of (NH4)2SeO4 (from 2.739 to 5.502u2009molċkg−1) and K2SeO4 (from 1.086 to 4.742u2009molċkg−1) in H2O at 298.15u2009K. The Pitzer ion-interaction model has been employed for the thermodynamic analysis of the results. The optimum values of the binary parameters of ionic interaction have been calculated, and important thermodynamic characteristics of (NH4)2SeO4 and K2SeO4 have been determined.Zusammenfassung.u2002Die isopiestische Methode wurde zur Bestimmung der osmotischen Koeffizienten binaürer Loüsungen von (NH4)2SeO4 (2.739–5.502u2009molċkg−1) und K2SeO4 (1.086–4.742u2009molċkg−1) in H2O bei 298.15u2009K benutzt. Die Ergebnisse wurden mit Hilfe des Pitzer-Modells thermodynamisch analysiert. Optimale Werte der binaüren Parameter der interionischen Wechselwirkung wurden berechnet, und wichtige thermodynamische Charakteristiken von (NH4)2SeO4 und K2SeO4 wurden bestimmt.