Thermodynamic Solubility Product Constants Research Articles

Study on deposit formation model in sulfide-containing natural gas environment

The breathing pipe of a produced water storage tank in a sulfide-containing natural gas station is prone to deposit formation, which leads to pipeline blockage. In this study, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analyses of the deposit in breathing pipe show that the deposit is composed of elemental sulfur and corrosion scales of ferrous polysulfide and ferrous sulfate. Existing deposit formation prediction models cannot predict the formation of elemental sulfur and corrosion scales in sulfide-containing environments. Herein, based on thermodynamic models of elemental sulfur and corrosion scale formation, deposit formation models of elemental sulfur, ferrous polysulfide, and ferrous sulfate scale formation are established. It is found that deposition of elemental sulfur and ferrous polysulfide increases with decreasing temperature of the breathing tube. Corrosion of pipe in the precipitating corrosive water leads to higher activity of left[{mathrm{Fe}}^{2+}right] on the inner wall of the pipe carried by the sulfide-containing natural gas. Consequently, ferrous polysulfide and ferrous sulfate are easily deposited when the activity products of ferrous, sulfide, and sulfate ions are higher than the thermodynamic solubility product constant. The aforementioned prediction models are applied to predict the deposition of ferrous polysulfide, ferrous sulfate corrosion scale, and elemental sulfur using the chemical composition data of gas and precipitating water in the breathing pipe of the produced water tank of TB101-X1 well. The prediction results of the models are consistent with those of actual chemical composition analysis, which verifies the accuracy and reliability of the models.

Insights into the Composite Scale Formation and Coprecipitation Behavior of CaSO4 and SrSO4 at different salinity level

The dependency of the calcium sulfate (CaSO4) deposit formation on the presence and concentration of co-precipitating ions, is a fundamental question to the advancement of crystallization science. In this paper, the thermodynamics and kinetics of the static precipitation of 47.5 mM calcium sulfate, in isolation and presence of strontium sulfate (SrSO4) as common co-crystallizing salt, are examined at 30°C. The deposition of pure and composite sulfate scales is studied by varying the salinity of the medium from 0.35 to 1.50 M NaCl. To evaluate the effect of the co-precipitating, strontium ion concentration was altered from 0 to 20.0 mM. In order to elucidate the crystallization mechanism in terms of reaction rate and extent, the concentration of the free scaling ions, including that of Ca2+, SO42− and Sr2+, is systematically monitored at different intervals until equilibrium is achieved. Moreover, crystal deposits collected at regular intervals from the isothermal incubation experiments are characterized for changes in their microstructure, morphology, and elemental distribution, to establish correlations with the data obtained on the evolution of the solution composition. The analysis of the crystallographic properties of the deposits substantiates the dependency of the thermodynamics and kinetics of the CaSO4 precipitation process on the salinity and co-existence of supersaturated SrSO4 in the mixture. Particularly, the morphology of calcium sulfate deposits is altered in the presence of SrSO4, which corroborates the assumption of co-crystal interactions. These results indicate that heterogeneous crystal nucleation and growth of the mixed salts can be prompted at temperatures and salinity conditions as low as 30°C and 0.35 M, when the concentration of Sr2+ is increased up to 20.0 mM. Using the Pitzer model derived ion activity coefficients, discrepant thermodynamic solubility product constant (Ksp) values are also determined for the pure salts when these co-precipitate in mixed systems. Reaction kinetics for calcium sulfate crystallization is also highly sensitive to the ionic strength effect as well as to the presence and concentration of strontium ions. Accordingly, these observations confirm the need to account for both contributing and non-contributing ions in assessing the thermodynamics and kinetics of crystal formation.

Modeling the Osmotic and Activity Coefficients of Lanthanide Nitrate Aqueous Solutions at 298.15 K from Low Molalities to Supersaturation

This article is a contribution to the modeling of the thermodynamic properties of 15 lanthanide (including lanthanum)-nitrate aqueous binary solutions, from low molalities to saturation (for Ce, Gd, Tb, and Tm) and supersaturation (for La, Pr, Nd, Sm, Eu, Dy, Ho, Er, Yb, and Lu) with respect to the corresponding trinitrate lanthanide solid salts. A critical compilation of the experimental and previous modeling data available in the literature is presented. The modeling approach is based on the standard Pitzer formulation for strong aqueous electrolytes, with two cases considered: three (beta((0)), beta((1)), and C-phi) or five (beta((0))), beta((1)), beta((2)), alpha(2), and C-phi) parameters. The best fits are obtained for the latter case, leading to the representation of unprecedented accuracy for the osmotic and activity coefficients over the whole range of experimental data up to the saturation/supersaturation points. On the basis of the models developed, the thermodynamic solubility product constants and the standard molar Gibbs free energy of formation of precipitating hexahydrate or pentahydrate lanthanide-nitrate solids are calculated.

Thermodynamic Investigation of NaClO3 Solubility in the Mixed Solvent Medium and the Related Ion – Pair Formation at Different Temperatures

Using the evaporating method, the solubility of sodium chlorate was determined in the various mixed solvents (water + ethanol + propanol) at various temperatures. The results showed that the solubility of NaClO3 decreases with increasing the mass percent of ethanol and propanol. On the other hand, the solubility of NaClO3 increases with increasing the temperature. In addition, the equilibrium constant of ion pair formation, KIP, for the reaction Na+(aq) + ClO3-(aq) -->Na+ClO3- (Ion Pair) was estimated upon Fuoss contact ion pair model and then, the values of ion-pair concentrations were determined by using the extended Debye-Hückel model and iteration calculations in various mixed solvents and various temperatures . Finally the value of thermodynamic solubility product constant, Ksp(th), and the values ∆H°, ∆S° and ∆G° of ion-pair formation were estimated in the mixed solvent media.

Thermodynamic Investigation of NaClO3 Solubility in the Mixed Solvent Medium and the Related Ion – Pair Formation at Different Temperatures

Using the evaporating method, the solubility of sodium chlorate was determined in the various mixed solvents (water + ethanol + propanol) at various temperatures. The results showed that the solubility of NaClO 3 decreases with increasing the mass percent of ethanol and propanol. On the other hand, the solubility of NaClO 3 increases with increasing the temperature .In addition, the equilibrium constant of ion pair formation, K IP, for the reaction Na + (aq) + ClO 3 - (aq) Na + ClO 3 - (Ion Pair) was estimated upon Fuoss contact ion pair model and then, the values of ion-pair concentrations were determined by using the extended Debye-HA¼ckel model and iteration calculations in various mixed solvents and various temperatures . Finally the value of thermodynamic solubility product constant, K sp(th) , and the values I”H ° , I” S ° and I” G ° of  and of ion-pair formation were estimated in the mixed solvent media.

Solubility Pattern of CaSO4·2H2O in the System NaCl + CaCl2 + H2O and Solution Densities at 35 °C: Non-ideality and Ion Pairing

The solubility of CaSO4·2H2O was determined in aqueous NaCl solutions up to very high salinities and constant CaCl2 concentrations at 35 °C. Addition of CaCl2 into the aqueous NaCl system reduces the solubility of CaSO4·2H2O quite dramatically while maintaining the basic pattern of the solubility curve. Mean ionic activity coefficients γ± of CaSO4·2H2O derived using the extended Debye−Hückel law with quadratic terms decrease with an increase in ionic strength. A comparison of the value of the thermodynamic solubility product constant, Ksp(th) of CaSO4·2H2O to the solubility product Ksp obtained from the observed solubility data indicate sizable differences. This has been explained through a combination of the extended Debye−Hückel law and ion association theory. We also measured accurate densities for the quaternary system CaSO4·2H2O + NaCl + CaCl2 + H2O at 35 °C. The density of the solution increases linearly with an increase in concentration. Solutions containing higher amounts of CaCl2 were found to be less dense when compared at the same ionic strengths. Solubility and density data as a function of concentration have been correlated using polynomial and linear fits by the method of least squares. These studies are of relevance in the production of salt with low impurities of Ca2+ and SO42- ions.

Non-ideality and ion-pairing in saturated aqueous solution of sodium fluoride at 25 °C

Using Solvent Evaporating and Atomic Emission Spectrophotometric methods, the solubility of NaF in water at 25 °C was determined. Comparing the value of the thermodynamic solubility product constant, K sp(th), ( K sp(th) = exp(− Δ G diss° / RT)) of NaF to the value which is obtained from the observed solubility, s/mol L −1 , and activity coefficients, f + and f −, which are estimated upon the extended Debye–Hückel law, K sp′ = [Na +][F −] f + f −, revealed a great difference. The difference has satisfactorily been explained using a combination of Debye–Hückel law and Ion-Association Theory.

Thermodynamic Solubility Constant of Ca(OH)2 in Simulated Radioactive Sulfate Liquid Waste

The thermodynamic solubility product constant (Ksp) of Ca(OH)2 in simulated radioactive sulfate liquid waste was experimentally determined at temperatures of 25° and 40°C. Synthetic solutions were prepared with pH ranging from 12.6 to >14 and ionic strength ranging from 0.25M to 3.7M. All the solutions were saturated in CaO and contained Na2SO4 to simulate the salts accompanying radioactive liquid waste. The Bromley model was applied to estimate the global ionic activity coefficients, and the Ksp value was compared with those found in the literature. The stability ranges of the different compounds formed as a function of pH were determined by X-ray diffractometry analysis, and their quantification was conducted by thermal analysis.

Determinação de parâmetros físico-químicos com um sensor potenciométrico sensível ao íon p-aminobenzoato

Este trabalho descreve a construção e a determinação de parâmetros físico-químicos com um eletrodo de segunda ordem do tipo, Pt|Hg|Hg2(PAB)2|Grafite, sensível ao íon p-aminobenzoato (PAB). O eletrodo é construído facilmente, apresenta um rápido tempo de resposta, é de baixo custo e tem um tempo de vida útil superior a 12 meses. Utilizando o referido eletrodo foi possível estimar os coeficientes de atividade iônica individuais do PAB, a 25ºC, em força iônica ajustada entre 0,700-3,000 mol L-1 com NaClO4, em solução aquosa. O potencial molal padrão do eletrodo determinado a 25ºC é de (445,5 ± 0,5) mV. A constante termodinâmica do produto de solubilidade, T Kps (I=0) do Hg2(PAB)2 determinada com o eletrodo é de (T Kps = 2,50 x 10-12 mol³ L-3 , a 25ºC). Uma característica favorável consiste no fato de que o eletrodo pode ser utilizado para determinar a concentração de íons p-aminobenzoato livres em sistemas complexos de íons metálicos.

Solution Equilibria for Uranium Ore Processing: The BaSO 4-H 2SO 4-H 2O System and the RaSO 4-H 2SO 4-H 2O System

A radio-tracer determination of the solubility of BaSO 4 in H 2SO 4-H 2O mixtures was undertaken at temperatures of 25°C and 60°C. These were subsequently modelled using the Pitzer model for the activity coefficients, and estimates were made for Ba 2+-SO 4 2− and Ba 2+-HSO 4 − interaction parameters. The final model yields an excellent description of the solubility of BaSO 4 in H 2SO 4-H 2O mixtures up to 6 mol/kg and at both 25°C and 60°C. The logarithm of the thermodynamic solubility product constant (log K sp) for barite obtained by regression analysis was −10.02 ± 0.02 at 25°C and −9.68 ± 0.01 at 60°C. The values of the ion association constant derived from these data are 2.49 ± 0.03 at 25°C and 2.55 ± 0.1 at 60°C. The enthalpy of dissolution for BaSO 4 was estimated to be 17.6 ± 0.2 kJ mol −1. Literature solubility data for the RaSO 4-H 2SO 4-H 2O system have also been interpreted, using the Pitzer model for the necessary activity coefficients. The logarithm of the thermodynamic solubility product constant (log K sp) for radium sulfate obtained was −10.21 ± 0.06 at 25°C, while the value of the ion association constant derived is 2.76 ± 0.05 at 25°C. The high negative value of the Pitzer parameter β 2 obtained by regression analysis of these data suggests that the explicit recognition of a RaSO 4(aq) ion association species is to be preferred in this case.

Thermodynamics of silver-silver ion electrode in acetonitrile-water mixtures

From the electromotive force (e.m.f.) measurements of cells with liquid-junction potentials, the standard potentials of the silver electrode were obtained in 5%, 10% and 15% (w/w) acetonitrile-water mixtures at five different temperatures ranging from 15 to 35 °C. Standard thermodynamic quantities for the cell reaction were estimated. Thermodynamic solubility product constants of silver halides were computed. The results are discussed in terms of ion solvation.

Precipitation of NH4UO2PO4.3H2O - Solubility and structural comparison with alkali uranyl(2+) phosphates

Precipitates formed in the system UO2(NO3)2-NH4OH-H3PO4-H2O, aged for 30 days at 298 K, were studied. The precipitates were characterized by chemical and thermogravimetric analyses, x-ray powder diffraction, infrared spectroscopy, polarized light microscopy, and by their fluorescent properties. The precipitation boundary was established tindallometrically and microscopically. On the basis of these measurements, the stability conditions, structural parameters, and solubility of the tetragonal polymorph of NH4[UO2PO4]·3H2O were determined. This compound shows a close structural relationship with H3O[UO2PO4]·3H2O (space group P4/ncc) and alkali uranyl(2+)phosphates polyhydrates M[UO2PO4]·nH2O (n =4 for M=Li; n =3 for M=Na, K, Rb and n =2.5 for M=Cs). The unit-cell dimensions determined for NH4UO2PO4·3H2O are: a=b=7.02 Å, c=18.08 Å (P4/ncc). The thermodynamic solubility product constant, Ks=a(NH4+)×a(UO22+)×a(PO43−), for NH4UO2PO4·3H2O was determined: log Ks= −26.50±0.09. The Ks values of M[UO2PO4]·n H2O (at ionic strength, I=0.23 mol dm−3) calculated from previously published experimental data by using correct stability constants of uranyl(2+)phosphate complexes are: log Ks=−22.61±0.08 for M=Na;log Ks= −23.92±0.12 for M=K;log Ks= −24.13±0.19 for M=Rb;log Ks= −23.80±0.20 for M=Cs; andlog Ks= −24.74±0.10 for M=NH4,showing that NH4UO2PO4·3H2O is less soluble than corresponding alkali uranyl(2+)phosphates.

Standard thermodynamics of transfer: III. Silver and silver salt electrodes in water + mono- and + dihydric alcohol mixtures

The standard thermodynamic quantities of transfer of Ag +, X − (X = N 3, CNS), Y 2− (Y = SO 4, CrO 4, Cr 2O 7) and Z 3− (Z = PO 4 or AsO 4) ions have been evaluated in water + 10 and + 20 mass% methanol, ethanol, 1-propanol and 2-propanol, and in water +10 and + 30 mass% ethylene glycol. The thermodynamic solubility product constants of silver salts in these solvents have been determined.

Standard thermodynamics of transfer: IV. The silver and silver salt electrodes in acetic acid + water mixtures at 25 °c

The standard transfer free energy changes for Ag +, IO − 3 and BrO − 3ions in 10, 20, 40 and 60 wt% acetic acid mixtures have been evaluated. The thermodynamic solubility product constants of silver halides, pseudo-halides and oxy halides in these solvents have been calculated.

Standard thermodynamics of transfer. I. Silver and silver salt electrodes in glycerol + water mixtures

The standard thermodynamic quantities of transfer of Ag +, X −, Y 2− and Z 3− ions (X = N 3, CNS, IO 3, BrO 3, VO 4; Y = SO 4, CrO 4, Cr 2O 7, WO 4; Z = PO 4, AsO 4) in water plus 5, 10, 20 or 30 wt% glycerol have been evaluated. The thermodynamic solubility product constants of silver salts in these solvents have been calculated.

Thermodynamics of silver—silver halide electrodes and thermodynamic solubility products of silver halides in glycerol + water mixtures at different temperatures

The standard potentials of silver—silver bromide and silver—silver iodide electrodes in glycerol+water mixtures containing 5, 10, 20 and 30 wt% glycerol were determined from electromotive force measurements of the cell Ag(s), AgX(s), KX(c)//KCl(c), AgCl(s), Ag(s), where X is Br or I, at seven different temperatures in the range 5–35°C. The standard potentials in each solvent are represented as a function of temperature. The standard thermodynamic functions for the electrode reactions, the primary medium effects of various solvents upon X −, and the standard thermodynamic quantities for the transfer of 1 g-ion of X − from water to the respective glycerol + water media are evaluated and discussed in the light of ion—solvent interactions as well as the structural changes of the solvents. From the values of the Ag/Ag + and Ag/AgX, X − electrodes, the thermodynamic solubility product constants of silver chloride, silver bromide and silver iodide have been determined in glycerol + water solvent mixtures at different temperatures.

Standard potentials of silver-silver ion electrode and thermodynamic solubility product constants of Ag X ( X = Cl, Br, I or CNS) in glycerol + water mixtures at 25°C (298.15K)

Standard potentials of silver-silver ion electrode and thermodynamic solubility product constants of Ag X ( X = Cl, Br, I or CNS) in glycerol + water mixtures at 25°C (298.15K)

Thermodynamic properties of the silver ion in alcohol + water solvent mixtures from electromotive force measurements and thermodynamic solubility product constants of AgX (X = Cl, Br, I or CNS) at different temperatures

The standard potentials of the silver-silver ion electrode in alcohol+water solvent mixtures containing 10 and 20 wt% methanol, ethanol, 1-propanol and 2-propanol have been determined from the electromotive force measurements of the cell Ag(s), AgCl(s), NaCl(c), NaNO 3(c)// NaNO 3(c), AgNO 3(c), Ag(s) at seven different temperatures in the range 5–35°C. The standard potentials in each solvent have been represented as a function of temperature. The standard thermodynamic functions for the electrode reaction, the primary medium effects of various solvents upon Ag +, and the standard thermodynamic quantities for the transfer of 1 g-ion of Ag + from water to the respective alcohol + water media have been evaluated and discussed in the light of ion-solvent interactions as well as the structural changes of the solvents. From the values of the standard potentials of the Ag/Ag + and Ag/AgX, X − electrodes, the thermodynamic solubility product constants of silver chloride, silver bromide, silver iodide and silver thiocyanate have been determined in alcohol + water solvent mixtures at different temperatures.

Thermodynamics of the silver-silver ion electrode and thermodynamic solubility product constants of silver halides and pseudo-halides in urea-water mixtures

Thermodynamics of the silver-silver ion electrode and thermodynamic solubility product constants of silver halides and pseudo-halides in urea-water mixtures

The hydrogen fluoride solvent system-V: The thermodynamic solubility product constant of CaF2 and the basicity of water in liquid HF

Activity coefficients for CaF2 in liquid HF were determined by solubility measurements on CaF2 in the presence of varying concentrations of NaF ranging from 0·1175 to 0·7295 moles per 1000 g of HF. The thermodynamic solubility product constant of CaF2 in liquid HF was determined to be 1·525 × 10−3 at 0°C. From the effect of small amounts of water on the solubility of CaF2 in liquid HF, a minimum ionization constant of 0·55 for water as a base in HF was determined at the same temperature.