Pitzer Ion-interaction Model Research Articles

Modeling geochemical factors controlling fluoride concentration in groundwater

The fluoride in groundwater can affect human health. The concentration of fluoride ions in groundwater is influenced by geogenic processes and is limited by the solubility of fluoride-containing minerals, especially fluorite. In this work, we summarize and assess fluorite solubility and the Pitzer interaction model parameters of related species, by which a quantitative model for calculation of the phases and chemical speciation in the Na–Ca–H–F–Cl–SO4–OH–HCO3–CO3–CO2–H2O aqueous system for temperatures 0–100 °C, and a pressure of 1 bar was established. Based on this model, we evaluate factors that govern the levels of fluoride, e.g. temperature, solution composition, pH, CO2 partial pressure, and concentration of carbonate minerals in the aquifer. The fluorite solubility increases with temperature and varies in different aqueous solutions. The fluoride concentration is highest in NaHCO3 type aqueous solutions. In acidic solution, HF is the dominant species, and free fluoride becomes dominant with increasing pH. Dissolved CO2 in solution slightly increases the concentration of fluoride in non-bicarbonate aqueous solution and non-calcite-bearing aquifer systems. In contrast, it has a significant negative effect in calcite and bicarbonate-bearing aquifer systems, where it greatly decreases the fluoride concentration. In calcite-bearing aquifer systems, the fluoride concentration is lower than in non-calcite mineral aquifer systems.

Thermodynamic properties determination of aqueous mixtures of CaCl2 and Ca(NO3)2 by the potentiometric method at T = 298.15 ± 0.1 K

The main goal of this work is to provide precise thermodynamic data about the ternary system (CaCl2+Ca(NO3)2+H2O), which may allow modeling its behavior. The Pitzer ion interaction model and Harned rule were used to illustrate the ternary electrolyte system. The activity coefficients were determined using a potentiometric method. The measurements were performed at T=298.15±0.1K and at total ionic strengths from (0.0010 to 5.0000)mol·kg−1. Different series of molal salt ratios were r=mCaCl2mCa(NO3)2=1.00, 2.50, 5.00, 10.00 and 15.00. The PVC based calcium ion-selective electrode (Ca2+-ISE), and the Ag/AgCl electrode used in this work were prepared in our laboratory. The mixing Pitzer parameters (θClNO3,ΨCaClNO3) were determined for this system. Then these parameters were used to calculate thermodynamic properties such as the osmotic coefficients (∅), the activity coefficients of Ca(NO3)2 in the mixture (γ±Ca(NO3)2) and the excess Gibbs free energy (GE). The experimental results showed that both Pitzer model and Harned rule were suitable to be used satisfactorily to describe this system.

The phase equilibriums in the NH4Cl-CaCl2-H2O system at 50 and 75°C and their Pitzer model representations

The solubilities and refractive indexes in the NH4Cl-CaCl2-H2O system were measured at 50 and 75°C and the phase diagrams were constructed on the basis of the experimental data. The mixing parameters and equilibrium constant Ksp were evaluated using the Pitzer ion-interaction model representations. The results obtained were in good agreement with the experimental data. The mixed parameters of Pitzer ion-interaction model and equilibrium constant obtained in the work can furthermore be applied to solubility predictions of more complicated systems containing NH4Cl and CaCl2.

Determination and modeling of activity coefficients of cobalt chloride in the (water + ethanol) mixed solvent system by potentiometric method at 298.15 K

In this work, the thermodynamic properties of (CoCl2+C2H5OH+H2O) system were investigated by potentiometric method and based on Pitzer ion interaction model. For this purpose, primarily the mean activity coefficients of CoCl2 in pure water and ethanol–water mixture solvent were determined using a galvanic cell without liquid junction potential of type: Co2+-ISE|CoCl2 (m), C2H5OH (wt.%), H2O (100-wt.%) |Ag·AgCl. The measurements were performed at T=298.15K and at total ionic strengths from 0.001 to 6.000mol·kg−1 in various ethanol–water mixed solvent systems containing 0, 10, 20, 30, 40 and 50% mass fractions of ethanol. The mean activity coefficients measured were correlated with Pitzer ion interaction model and the Pitzer adjustable parameters were determined. Then these parameters were used to calculate the thermodynamics properties for under investigated system. The results showed that the Pitzer ion interaction model can satisfactory describe the investigated system. The modified three-characteristic-parameter correlation (TCPC) model was applied to correlate the experimental activity coefficient data for under investigation electrolyte system, too. The results showed that the modified TCPC model also was suitable in the case of the mixed solvent system.

Apparent molar volume and modeling of volumetric properties of ionic liquid aqueous solutions 1-butyl-3-metilmidazolium chloride [Bmim+][Cl-] at various temperatures

Densities of the aqueous solutions of ionic liquid 1-butyl-3 metilmidazolium chloride [Bmim + ][Cl - ] were determined using a vibrating tube densitometer Anton Paar DMA 5000 at a temperature range between (283.15 - 218.15) K. The apparent molar volumes V f of aqueous chloride1-butyl-3-methylimidazolium were calculated and adjusted to the Pitzer ion interaction model, obtaining the limiting apparent molar volumes V f and Pitzer volumetric parameters b (O) M V X , b (1) M V X , C V MX at temperatures of 283.15, 288.15, 293.15, 298.15, 303.15, 313.15 and 318.15K, proving that this model adequately represents the experimental volumetric data below an ionic strength of 0.6018 mol / kg. Finally the limiting apparent molar expansibilities f O E were calculated from the limiting apparent molar volumes at various temperatures and the results are discussed in terms of the interactions occurring in solution.

Thermodynamic investigation of the ternary mixed electrolyte (NaCl + Na2HCit + H2O) system using potentiometric measurements at T = (298.2 and 308.2) K

In this work, the mean activity coefficients of NaCl in the (NaCl+Na2HCit+H2O) ternary mixed electrolyte system were determined using the potentiometric method. The potentiometric measurements were carried out on the galvanic cell without liquid junction of the type: Na-ISE/NaCl (m1), Na2HCit (m2), H2O/Ag–AgCl over total ionic strengths from (0.01 to 4.000)mol·kg−1. Different series of the salt molal ratios r (r=mNaCl/mNa2HCit=0.1, 1, 2.5, 5.0, 7.5, 10.0) and pure NaCl were used for the measurement at T=(298.2 and 308.2)K and P=0.1MPa. The results were interpreted by using Pitzer ion-interaction model with and without higher-order electrostatic effects. The mixing parameters obtained were used to calculate the values of the mean activity coefficients of Na2HCit, the osmotic coefficients, solvent activity and the excess Gibbs free energies for the whole series of the studied mixed electrolyte system.

Predicting the solubility of SrSO4 in Na–Ca–Mg–Sr–Cl–SO4–H2O system at elevated temperatures and pressures

Precipitation of strontium sulfate (or SrSO4) has already been distinguished as one of the most costly and critical problems which may occur in process industries and oilfield operations. Costs due to scaling and remedial actions that need to be taken afterward are generally high owing to low solubility of SrSO4 in aqueous solutions. Therefore, a thorough understanding of the SrSO4 thermodynamic behavior under various operating conditions is vital to predict or even avoid the overall damage caused by scaling. The primary aim of this work is to develop a model based on Least Squares Support Vector Machine (LSSVM) and Coupled Simulated Annealing (CSA) referred to as CSA-LSSVM to predict strontium sulfate solubility as a function of pressure, temperature and ionic compositions. In this context, we have employed almost 1641 experimental data regarding strontium sulfate solubility to build a comprehensive model and to evaluate its reliability. The results show that the proposed model has a better performance in comparison with pre-existing empirical correlations used for predicting SrSO4 solubility and it is also in well accordance with experimental measurements. A comparison was also drawn between predictions of Pitzer ion interaction model with CSA-LSSVM model forecasts in terms of sensitivity analysis and single point solubility predictions. The whole dataset was analyzed at the end to diagnose the possible outliers and to investigate the reliability of recorded measurements. Based on the results obtained from this study, developed model could successfully be used in predicting SrSO4 solubility in aqueous Na–Ca–Mg–Sr–Cl–SO4–H2O system over temperature ranges from 2 to 253.5°C, and pressures from 1 to 568.51atm.

Prediction of the aqueous solubility of BaSO4 using pitzer ion interaction model and LSSVM algorithm

Deposition of barium sulfate (or BaSO4) has already been recognized as a devastating problem facing process industries and oilfield operations, mainly owing to its low solubility in aqueous solutions. Predicting and also preventing the overall damage caused by BaSO4 precipitation requires a profound knowledge of its solubility under different thermodynamic conditions. The main aim of this study is to develop a solubility prediction model based on a hybrid of least squares support vector nachines (LSSVM) and coupled simulated annealing (CSA) aiming to predict the solubility of barium sulfate over wide ranges of temperature, pressure and ionic compositions. Results indicate that predictions of the presented model are in well accordance with experimental measurements yielding overall correlation coefficient (R2) of 0.996 and total RMSE of 0.00077. Constructed model was also found to outperform a previously well-known correlation employed for predicting BaSO4 solubility in aqueous solutions. Solubility predictions based on Pitzer ion interaction model were also compared to CSA-LSSVM predictions in terms of single point estimations and sensitivity analysis. Results of this study suggest that CSA-LSSVM model could be implemented in assessing the solubility of BaSO4 in Na–Mg–Ca–K–Ba–Cl–SO4–H2O system over wide ranges of temperature from 0 to 279°C and pressures ranging from 1 to 1517 bars with an acceptable degree of accuracy.

Thermodynamic model for the solubility of Ba(SeO4, SO4) precipitates

Abstract The solubility of Ba(SeO4, SO4) precipitates was determined as a function of the BaSeO4 mole fractions, ranging from 0.0015 to 0.3830, and time with an equilibration period extending to as long as 302 days. Equilibrium/steady state conditions in this system are reached in ≤ 65 days. Pitzer's ion interaction model was used to calculate solid and aqueous phase activity coefficients. Thermodynamic analyses showed that the data do not satisfy Gibbs-Duhem equation, thereby demonstrating that a single-solid solution phase does not control both the selenate and sulfate concentrations. Our extensive data with log 10 [Ba] ranging from − 3.6 to −5.9 mol kg –1, log 10 [SeO4] ranging from − 3.6 to −5.2 mol kg –1, and log 10 [SO4] ranging from − 4.0 to −5.3 mol kg –1 can be explained with the formation of an ideal BaSeO4 solid solution phase that controls the selenium concentrations and a slightly disordered/less-crystalline BaSO4(s) (log 10 K ○ sp =− 9.5 instead of − 10.05 for barite) that controls the sulfate concentrations. In these experiments the BaSO4 component of the solid solution phase never reaches thermodynamic equilibrium with the aqueous phase. Thermodynamic interpretations of the data show that both the ideal BaSeO4 solid solution phase and less-crystalline BaSO4(s) phase are in equilibrium with each other in the entire range of BaSeO4 mole fractions investigated in this study.

Long-term assessment of geochemical reactivity of CO2 storage in highly saline aquifers: Application to Ketzin, In Salah and Snøhvit storage sites

Saline aquifers are choice targets for geological storage of CO2 because of their storage potential and because these formations are not suitable for other uses. Geochemical modeling is an interesting tool to assess the geochemical behavior of CO2 in the saline aquifer, including its dissolution in the brine and its interactions with minerals. Two key parameters which determine the confidence one can have in the results of geochemical modeling are tested in this paper: (i) the establishment of the conceptual model, including the selection of the primary and secondary minerals expected to react; and (ii) the activity model and the associated thermodynamic databases to calculate the interaction energies within the saline solution. In this study, we performed an analysis of a large set of CO2 storage natural analogs, which makes it possible to identify the minerals that are likely to precipitate and dissolve during CO2–brine–rock interactions. Interestingly, this analysis indicates a strong dependence of Dawsonite precipitation on the initial sandstone mineralogy. Dawsonite can precipitate in lithic and feldspar rich sandstones but was not observed in quartz rich sandstones. These observations on mineral reactivity are used to establish reactivity conceptual models for three CO2 storage case-studies in saline sandstone aquifers (Ketzin, In Salah and Snøhvit) and a methodology is proposed to evaluate the long-term geochemical reactivity of these saline aquifers as a result of CO2 injection. Noticeable differences are obtained between the case-studies as a function of the initial mineralogy and chemical conditions in the sandstones, which highlight that CO2 mineral trapping can take place in a given storage site but can be almost absent in other storage sites. Regarding the activity model and the database, the Pitzer interaction model is rarely used for simulating CO2 geochemical behavior in saline aquifers despite the fact that more conventionally used activity models are not valid for such salinities. A comparison between calculated mineral solubility evolution with salinity versus experimental data is performed here using both B-dot and Pitzer activity models as well as six different databases. This comparison exercise shows that chemical interactions within saline solutions can only be reproduced using the Pitzer model, even though Pitzer databases are still incomplete or are not coherent for a wide range of chemical species and temperatures. The geochemical simulations of CO2 injection in Ketzin, In Salah and Snøhvit saline aquifers give divergent results using different activity models and databases. A high uncertainty on the simulation results is then linked to the database choice and this study clearly stresses the need for a Pitzer database that can be confidently used in all physical/chemical conditions found in deep sedimentary aquifers.

Isopiestic Studies on Rare Earth Chloride Quaternary System (H2O + LaCl3 + PrCl3 + NdCl3) and Ternary Subsystems

Isopiestic measurements have been carried out for the quaternary system H2O + LaCl3 + PrCl3 + NdCl3 and its ternary subsystems H2O + LaCl3 + PrCl3, H2O + LaCl3 + NdCl3, and H2O + PrCl3 + NdCl3 at 298.15 K. The results are well represented by the partial ideal solution model and the modified Pitzer ion-interaction model extending to C(3) over full concentration range.

Determination and modeling of activity coefficients of the ionic liquid 1-ethyl-3-methylimidazolium chloride in the (water + formamide) mixed solvent system at 298.2 K

In this work, the results relating to the mean activity coefficient measurements for 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl) in the (formamide+water) mixed solvent system using the potentiometric method have been reported. The electromotive force (emf) measurements were performed on the galvanic cell of the type: Ag|AgCl|[EMIm]Cl (m), formamide (wt.%), H2O (1−wt) %|EMIm-ISE, in various mixed solvent systems containing 0, 10, 20, 30, and 40% mass fractions of formamide over ionic strength ranging from 0.0010 to 2.5000mol·kg−1 at T=298.2K. The modeling of this ternary system was made based on the Pitzer ion-interaction model. The values of the mean activity coefficients, the osmotic coefficients, the excess Gibbs free energy and the solvent activity together with Pitzer ion-interaction parameters (β(0), β(1) and Cϕ) for the series under investigated system were determined.

Monetite promoting effect of NaCl on brushite cement setting kinetics.

Brushite forming calcium phosphate cements (CPCs) have received growing interest for scaffold applications due to their high surface area and high bioresorbability. The dehydrated form of brushite, monetite, has a finer microstructure with higher surface area, higher strength and bioresorbability comparable to brushite, making it a viable alternative phase in CPCs. The increase in monetite content of the β-tricalcium phosphate (β-TCP)-monocalcium phosphate monohydrate (MCPM) cement system due to the reduction in its supersaturation upon addition of NaCl to excess setting liquid was investigated kinetically. The relaxation period was monitored by pH-stat titration of the cement solution by 0.1 M NaOH. Monetite growth was achieved in shorter periods at higher NaCl concentrations where the supersaturation gap between brushite and monetite is thought to be narrowed due to high ionic strength in accord with Pitzer's ion interaction model. The brushite/monetite ratio decreased consistently with increasing NaCl concentration in the 3-6 M range.

The free proton concentration scale for seawater pH

Due to the use of multiple pH scales in seawater, studies related to the pH of marine environments are unnecessarily complicated and prone to inaccuracy. It is desirable that a standard scale be adopted, and we suggest the free proton pH scale be used. To ensure that the free proton scale is accurate and consistent with primary pH measurements in seawater, we use the Pitzer ion-interaction model to re-evaluate the free scale pH and stoichiometric dissociation constants of HSO4− and H2CO3. The Pitzer model is validated over a salinity range of 5 to 45 and temperatures of 0 to 45°C using the measured mean activity coefficient of HCl in artificial seawater. The resulting standard potential and stoichiometric dissociation constants are compared to previous estimates. The validated model results are used to evaluate more accurate values for the pH of equi-molal (m=0.04molkg−1) amine buffers on the free proton concentration scale, which can be used to calibrate free scale pH measurements in natural waters.

Determination of thermodynamic properties of the ternary electrolyte system {CoCl2 + Co(NO3)2 + H2O} by the potentiometric method at T = 298.15

In this work, the Pitzer ion interaction model and Harned rule were used to illustrate the ternary electrolyte system {CoCl2+Co(NO3)2+H2O}. The activity coefficients were determined using a potentiometric method. The galvanic cell used had no liquid junction of type: Co2+-ISE|CoCl2 (mA), Co(NO3)2 (mB), H2O|Ag.AgCl. The measurements were performed at T=298.15K and at total ionic strengths from 0.001 to 6.000mol·kg−1 for different series of salt ratios r=mCoCl2mCo(NO3)2=1.00, 2.50, 5.00, 7.50, 10.00 and 15.00. The PVC based cobalt ion-selective electrode (Co2+-ISE), the PVC based nitrate ion-selective electrode (NO3−-ISE) and the Ag/AgCl electrode used in this work were prepared in our laboratory and showed a reasonably good Nernst response. The experimental results showed that both Pitzer model and Harned rule were suitable to be used satisfactorily to describe this ternary system.

Modelling of salt crystallization in building materials with microstructure – Poromechanical approach

A novel mathematical model of chemo-hydro-thermo-mechanical behavior of porous building materials considering salt transport and crystallization is presented in the paper. The additional pressure, which is generated during the salt crystallization, is taken into account by means of the effective stress principle. The solid surface fraction in contact with the growing crystal is calculated based on the pore distribution model obtained by mercury intrusion porosimetry. The Pitzer ion interaction model and the Freundlich non-equilibrium isotherms are utilized to define the kinetics of salt crystallization/dissolution. The properties of the solution and the magnitude of crystallization pressure depends on the internal pore structure of the material. The model equations are solved by means of the finite element and finite difference method. Some test problems, as well as the drying examples of brick and concrete wall saturated with the NaCl solution, are presented.

Thermodynamic study of (KCl + proline + water) system based on potentiometric measurements at T = (298.2 and 303.2) K

In this paper, the results relating to the thermodynamic properties of (KCl+proline+water) system using the potentiometric method are reported. The electromotive force (emf) measurements were performed on the galvanic cell of the type: Ag|AgCl|KCl (m), proline (w%), H2O (1−w)%|K-ISE, in various mixed solvent systems containing 0, 2.5, 5.0, 7.5, 10.0 and 12.5% mass fraction of proline over ionic strength ranging from 0.0010 to 3.9578mol.kg−1 at T=(298.2 and 303.2)K. The modeling of this ternary system was made based on the Pitzer ion-interaction model. The resulting values of the mean activity coefficients, the osmotic coefficients and the excess Gibbs free energy together with Pitzer ion-interaction parameters (β(0), β(1) and Cφ) for the series under investigated system are reported.

Thermodynamic study of the quaternary electrolyte (NaCl + NaNO3 + HCONH2 + H2O) system using potentiometric measurements at T = (298.2 and 303.2) K

In this work, the thermodynamic properties of the quaternary electrolyte (NaCl+NaNO3+HCONH2+H2O) system, using the potentiometric method, are reported. The potentiometric measurements were carried out on the galvanic cells without liquid junction of the types:Ag–AgCl|NaCl (mA), (100-w%) H2O+w% HCONH2|Na–ISE,Ag–AgCl|NaCl (m1), NaNO3 (m2), (100-w%) H2O+w% HCONH2|Na–ISE andNO3–ISE|NaNO3 (mB), (100-w%) H2O +w% HCONH2|Na–ISEover total ionic strengths from 0.001 to 4.000mol·kg−1. Different series of the salt molal ratios r (r=mNaCl/mNaNO3=0.1, 1, 2.5, 5.0, 10.0) and pure NaCl in mixed solvent system containing 10% mass fraction of formamide were used for the measurements at T=(298.2 and 303.2)K. The modeling of this quaternary system was made based on the Pitzer ion-interaction model. In according to Pitzer graphical method, the mixed ionic interaction parameters (θClNO3,ψNaClNO3) were evaluated for each series of the studied system. Then, the obtained parameters were used to calculate the values of the mean activity coefficients of NaNO3, the osmotic coefficients, solvent activity and the excess Gibbs free energies for the whole series of the studied mixed electrolyte system at T=(298.2 and 303.2)K.

Activity Coefficient Determinations of KCl in the KCl + Formamide + Water Mixed Solvent System Based on Potentiometric Measurements at 298.2 K

In this work mean activity coefficient measurements for KCl in the KCl + formamide + water system, using the potentiometric method, are reported. The electromotive force measurements were performed on a galvanic cell of the type Ag | AgCl | KCl (m), formamide (w%), H2O (1−w)% | K-ISE, in solvent mixtures containing w=(0,10,20,30, and 40)% mass percent of formamide over ionic strengths ranging from 0.0010 to 3.9578 mol⋅kg−1. Modeling of the activity coefficients of this ternary system was based on an extended Debye–Huckel equation and the Pitzer ion-interaction model. The resulting values of the mean activity coefficients, the osmotic coefficients and the excess Gibbs energy, together with Pitzer ion-interaction parameters (β(0), β(1) and Cϕ) and Debye–Huckel parameters (a, c and d), are reported for the investigated system.

Potentiometric determination of activity coefficients for NiCl2 in water + glucose mixtures at 298.15 K

In this work, the results relating to the mean activity coefficient measurements for NiCl2 in the NiCl2 + glucose + water system using the potentiometric method are reported. The potentiometric measurements were performed on the galvanic cell of the type: Ag|AgCl|NiCl2 (m), glucose (w%), H2O (1 − w)%|Ni-ISE, in various mixed solvent systems containing 0%, 10%, 20%, 30% and 40% mass fraction of glucose over ionic strength ranging from 0.0012 to 5.000 kg mol−1. The Pitzer ion-interaction model was used for the experimental data correlation and calculation of thermodynamic properties. The Pitzer ion-interaction parameters (β (0), β (1) and ) for each of the mass fractions of glucose were determined. Then, the obtained Pitzer parameters were used for the evaluation of the other thermodynamic properties such as of osmotic coefficients () and excess Gibbs free energy for the investigated system.