Phase equilibria determination for the Al + Fe(II) + Mg + Ca + K + Cl + H2O system showed that FeCl2 is effective to promote the salting-out crystallization of AlCl3·6H2O. A novel process to recover AlCl3·6H2O from fly ash by salting-out crystallization with FeCl2 is proposed and proven feasible. This novel process includes leaching of fly ash by hydrochloric acid, reduction of Fe3+ to Fe2+, salting-out crystallization of AlCl3·6H2O with FeCl2, and filtering followed by washing. The solubility of AlCl3·6H2O in the Fe(II) + Mg + Ca + K + Cl + H2O system was determined over the entire practical concentration range and from 283.2 to 363.2 K using a dynamic method. The experimental solubilities were regressed to obtain new mixed solvent electrolyte (MSE) model parameters. These new parameters were capable of accurately representing the experimental data of the system from 283.2 to 343.2 K. The phase diagram of the ternary AlCl3–FeCl2–H2O system at 298.2 and 333.2 K was successfully constructed with the aid of the new MSE model parameters. Based on the phase diagram, a promising route to recover AlCl3·6H2O by salting-out crystallization with FeCl2 was generated and verified to be feasible in laboratory experiments. All the results generated from this study will provide fundamental data for industrial applications aiming at the recovery of alumina from fly ash resources.

For development of the new process for the recovery of dilute sulfuric acid by azeotropic distillation proposed in our earlier publication [Li et al., Ind. Eng. Chem. Res., 2013, 52, 3481–3489], in this paper, the vapor–liquid equilibria (VLE) for the FeSO4 + H2O and H2SO4 + FeSO4 + H2O systems were first determined by the quasi-static ebulliometric method. The azeotropic temperatures of the H2SO4 + H2O + entrainer (cyclohexane and octane) systems were also measured. The corresponding electrolyte nonrandom two-liquid interaction parameters were obtained by regressing the experimental data with a maximum average absolute deviation of boiling points of 0.83 K. The model with newly obtained parameters was verified by comparing its prediction with the experimental azeotropic temperature for the H2SO4 + FeSO4 + H2O + C6H12 quaternary system. The temperature and sulfuric acid concentration ranges of the study were 305.9–396.9 K and 0–86.1 wt %, respectively. Following from the experimental results, semicontinuous distillation experiments for the sulfuric acid recovery were performed with cyclohexane as the entrainer. Equipped with the new parameters, Aspen Plus was adopted to carry out the process simulation for the recovery of dilute sulfuric acid by azeotropic distillation. The simulation results show that when cyclohexane was employed as the entrainer, the dilute sulfuric acid can be concentrated to 68% by a packed column containing 4 theoretical stages and with a reboiler temperature of only 361 K.

Vapor–liquid equilibria (boiling points) data for the ZnSO4–H2SO4–H2O and the MgSO4–H2SO4–H2O systems were determined by the quasi-static ebulliometric method at (30, 60, 90, and 101.3) kPa. The boiling points of the ZnSO4–H2O and the ZnSO4–H2SO4–H2O systems were used to regress new chemical model parameters with the average absolute deviation of only 0.08 K. The model was verified by comparing its predictions of the solubility of zinc sulfate in water from (273.15 to 310.15) K and the activity of water in zinc sulfate solution at 298.15 K with literature data. Furthermore, the distributions of the ZnSO4(aq) (ZnSO4 neutral species), Zn2+, MgSO4(aq) (MgSO4 neutral species) and Mg2+ species were predicted. The ZnSO4−H2SO4−H2O system speciation provided a thermodynamic basis for the empirically optimized zinc sulfate concentrations currently employed in the Zn electrowinning industry.

A novel azeotropic distillation for sulfuric acid recovery, which uses organic solvents as entrainers, is proposed. This new distillation process may provide significant energy savings. Vapor–liquid equilibria (VLE) data were determined by the quasi-static ebulliometric method for the following systems at (30, 60, and 90) kPa: (1) sulfuric acid + water + ethanol; (2) sulfuric acid + water + butyl acetate; and (3) sulfuric acid + water + butyl acetate + ethanol. Through the use of the OLI software, a chemical model was established via regressing the experimental data to obtain the mixed solvent electrolyte (MSE) model parameters. The average absolute deviations of boiling points for all systems are only 1.34 K. The new model with newly obtained parameters was successfully applied to predict the VLE for the sulfuric acid + water + butyl acetate ternary system at constant pressure, providing important VLE information for the recovery of spent sulfuric acid by this new azeotropic distillation technology.

The high temperature dissolution behavior of diaspore concentrate was measured in concentrated NaOH–NaAl(OH)4 solutions. The dissolution rate of Al was greatly found to be enhanced by increasing NaOH concentration and temperature while decreased with addition of Al(OH)3. The concentration of Si as the main impurity constantly decreases with reaction time while the Fe is retained at a limited level. The generalized rate law for mineral dissolution and precipitation, proposed by Lasaga (Lasaga, A. C. Kinetic Theory in the Earth Science; Princeton University Press: Princeton, NJ, USA, 1998), was applied to model the kinetic behavior of Al on the basis of KSP(diaspore) and the activity coefficients of related species in the solution. The resulting kinetic model was capable of predicting the dissolution rate of Al in the Bayer liquor. The apparent activation energy of the dissolution reaction over the temperature range from 473.2 to 543.2 K was estimated at 83 kJ·mol–1.

The vapor pressures of methylcarbamate (MC) and methyl n-phenyl carbamate (MPC), at different temperatures ranging from (341.45 to 418.45) K, have been measured using the quasi-static ebulliometric method. The experimental data were fitted to the Antoine equation with the overall average absolute deviation of pressure of 0.06 kPa. Isobaric vapor–liquid equilibrium (VLE) data were also determined for the MC and MPC system at (1.00, 2.00, 4.00, 6.00, and 8.00) kPa by the same method and were correlated with nonrandom two-liquid (NRTL) and Wilson models. The both model parameters were obtained with the overall average absolute deviation of temperature 0.82 K and 0.81 K. The relative volatility of the binary system was calculated and was more than 1 by far, indicating that high-purity MPC can be obtained from the binary mixture by distillation technology.

The solubility of ammonium metavanadate (NH4VO3) in ammonium salt solution is significant for the precipitation of NH4VO3from the vanadium-containing solution. The solubilities of NH4VO3 in the (NH4)2SO4–H2O, NH4Cl–H2O, and (NH4)2SO4–NH3–H2O systems were measured using dynamic method in the temperature range from (298 to 343) K. The investigated concentration is up to 3.0 mol·kg–1, 2.5 mol·kg–1, and 5.2 mol·kg–1 for (NH4)2SO4, NH4Cl, and NH3, respectively. The solubility of NH4VO3 decreases sharply with the addition of (NH4)2SO4 or NH4Cl while the solubility of NH4VO3 in the mixed NH3 and (NH4)2SO4 (0.10 mol·kg–1) solution increases first and then levels off with increasing NH3 concentration. The solubility product constant (KSP) of NH4VO3 was also determined using the standard-state thermodynamic data. The Bromley–Zemaitis model was applied to model the solubility of NH4VO3 in the systems mentioned above, and five pairs of new model parameters were obtained via the regression of the experimental solubilities. A chemical model was established to successfully calculate the solubility of NH4VO3 in all systems. All of the work done in this research will provide a thermodynamic basis for industrial development in the precipitation of NH4VO3.

Vapor–liquid equilibiria (VLE) were measured for systems containing 1-methyl-3-ethylimidazolium diethylphosphate ([EMIM][DEP]) ionic liquid (IL) in the temperature range from 310 K to 390 K. The systems include 1-propanol + [EMIM][DEP], 2-propanol + [EMIM][DEP], water +1-propanol + [EMIM][DEP], and water + 2-propanol + [EMIM][DEP]. [EMIM][DEP] was divided into one 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) and three methylene (CH2) electrically neutral groups. And then the experimental VLE data for binary systems containing [EMIM][DEP] were regressed using the modified UNIFAC model with the maximum average relative deviation (ARD) of 2.7 %. The newly obtained interaction parameters between groups allowed the reliable prediction of other binary and ternary systems containing [MMIM][DMP] and [EMIM][DEP] without parametrization. It was found that both of the ILs can give rise to the salting-out effect, and lead to a breaking of the azeotropic behavior of alcohols + water mixtures. [MMIM][DMP] shows a higher separation ability for the azeotropic mixture studied than [EMIM][DEP].

Octane was considered to be a potential entrainer for the recovery of spent sulfuric acid by heterogeneous azeotropic distillation. The vapor–liquid equilibria (VLE) data were determined for octane + ethanol, octane + water + ethanol, and octane + sulfuric acid + water + ethanol systems at (30, 60, 90, and 101.3) kPa using the ebulliometric method. The VLE data were used to regress the electrolyte nonrandom two-liquid interaction parameters with the help of Aspen Plus for pairs: C8H18–C2H6O, C8H18–H2O, H2SO4–C2H6O, C2H6O–[H3O]+:[HSO4]−, C2H6O–[H3O]+:[SO4]2–, C8H18–[H3O]+:[HSO4]−, and C8H18–[H3O]+:[SO4]2–. The correlation fitted the experimental data well for all the systems. The maximum absolute deviation and average absolute deviation for temperature for the systems are 0.86 K and 0.26 K, respectively.

The solubility of sodium aluminosilicate (sodalite), a major desilication product (DSP) in the Bayer process, in NaOH and NaOH–NaAl(OH)4 solutions was determined and modeled at temperatures from 303.2 to 348.2 K. Sodium aluminosilicate was synthesized in a batch crystallizer and the effect of temperature, solution concentrations, and aging time was investigated. Solubility was found to increase with increasing NaOH concentration while the solubility sharply decreases with the addition of Al(OH)3, reaches a minimum at about 0.8 mol·L–1, and then increases. A mixed-solvent electrolyte (MSE) model for the solubility of sodalite was developed with the help of the OLI platform via regression to obtain the model parameters. In addition, the desilication kinetics of NaOH–NaAl(OH)4 solutions by using sodalite as seeds was studied experimentally and modeled with the aid of a second order kinetic model. The activation energy of desilication over the temperature range 323.2–363.2 K was found to be 92 ± 14 kJ·mol–1. Under the optimal operation conditions, 80% silica was removed after 2 h.

The reactive crystallization kinetics of hydromagnesite (4MgCO3·Mg(OH)2·4H2O) for the MgCl2–Na2CO3–NaOH–H2O system has been systematically investigated in a continuously operated mixed-suspension mixed-product removal (MSMPR) crystallizer for the first time. Determination of the effects of reactive temperature and OH– ion on magnesium carbonate hydrates in the above system was conducted through a batch crystallization experiment, and the crystallization temperature of 80 °C for the precipitation of regular spherical-like hydromagnesite was selected for the kinetics study. The relative supersaturation for hydromagnesite is obtained based on the activity coefficients calculated by the Pitzer model. The growth rate, nucleation rate, and agglomeration kernel are determined on the basis of the agglomeration population balance equation, and their kinetic equations are then correlated in terms of power law kinetic expressions. The orders of volume growth rate and linear growth rate with respect to the relative supersaturation are 1.55 and 0.95, respectively. The magma density has an important effect on the nucleation rate of hydromagnesite particles. However, the expression of β ∝ MT–0.39 for hydromagnesite agglomeration shows that the magma density has a negative effect on the agglomeration kernel. All of these will provide a basis for the design and analysis of industrial crystallizers.

The phase equilibria of the glycine–KCl–NaCl–H2O system were determined in the concentrations up to 3.33 mol·kg–1 over the temperature range from 283.2 to 363.2 K using a dynamic method. A rigorous chemical model for the glycine–KCl–NaCl–H2O system was established by the Pitzer model with the help of an OLI platform. With the equilibrium constants of dissociation reactions obtained by standard-state thermodynamic data, the new Pitzer model parameters were harvested by regressing solubility of the system. These newly obtained parameters were used to accurately predict the multiple saturated points at the temperature range from 283.2 to 363.2 K. The phase behavior of the ternary glycine–KCl–H2O and glycine–NaCl–H2O system at 298.2 and 343.2 K were successfully visualized with lucidity on an equilateral triangle. To investigate the effect of glycine on the morphology of KCl, the KCl crystals were produced from glycine solution with different concentration (17–25% w/v) by evaporation at ambient temperature. The glycine (25% w/v)-modified KCl crystal changed its morphology from native cubic to hexagonal prism form with the angle of repose from 32° to 23.8–25.8°, indicating a good flowability and anticaking characteristics. Finally, KCl supersaturation variation with evaporation time was simulated with aid of the chemical model established in present study to elucidate the influence of glycine concentration on the anticaking characteristics of KCl crystal. All the results generated from this study will provide the fundamentals for industrial application to produce crystals with anticaking characteristics.

The solubilities of aniline hydrochloride ([HAE]Cl) in different aqueous solutions of methanol, ethanol, propan-1-ol, and their mixed solvent solutions were determined using the dynamic method in the temperature range between 288 K and 328 K. With the purpose of improving AspenPlus's prediction capability, in regards to [HAE]Cl solubilities in the CH3OH–C2H5OH–C3H7OH–H2O system at various temperatures, new interaction energy parameters τ[HAE]+-Cl–,CH3OHτCH3OH,[HAE]+-Cl–, τ[HAE]+-Cl–,C2H5OHτC2H5OH,[HAE]+-Cl–, and τ[HAE]+-Cl–,C3H7OHτC3H7OH,[HAE]+-Cl– were obtained via regression of the experimental solubility of [HAE]Cl in binary mixed solvent systems with the maximum-likelihood principle. With the newly obtained electrolyte nonrandom two-liquid (NRTL) interaction parameters, a self-consistent model was established for the calculation of [HAE]Cl solubility in the system of CH3OH–C2H5OH–C3H7OH–H2O as a function of temperature and the composition of solvents. The maximum relative deviation between experimental and predicted solubility data is 2.3 %, and the average relative deviation is 1.8 %.

The separation of butyl acetate from aqueous solution by distillation is energy-consuming. However, azeotropic distillation may be a commercially economical way when cyclohexane is added as an entrainer. The vapor–liquid equilibria (VLE) data were measured by the quasi-static ebulliometric method for the following systems at (29.77, 58.85, and 87.65) kPa: (1) butyl acetate + cyclohexane; (2) water + butyl acetate + ethanol; (3) water + butyl acetate + cyclohexane; (4) water + ethanol + butyl acetate + cyclohexane. The VLE data for binary and ternary systems were used to regress the nonrandom two-liquid (NRTL) interaction parameters, namely, pairs of butyl acetate–cyclohexane and water–butyl acetate, with aid of Aspen Plus platform. The newly regressed parameters were verified by the comparison between predicted VLE values and experimental data for ternary and quaternary systems without parametrization. The average relative deviations are only 0.19 % and 0.17 %, respectively. Furthermore, the NRTL thermodynamic model with new parameters was applied to construct the distillation residue curve map for the water + butyl acetate + cyclohexane ternary system, which provides the VLE information for the production of the butyl acetate by new azeotropic distillation.

The solubility of gypsum (CaSO4·2H2O) in ammonium solutions plays a significant role to prevent gypsum scaling on the heater and tower in the treatment of ammonium-N wastewater bearing sulfate ions by the steam stripping process. In this work solubilities of calcium sulfate dihydrate in NH4Cl, NH4NO3, and mixed NH4Cl and (NH4)2SO4 solutions up to 343.15 K were measured using the classic isothermal dissolution method. The investigated concentration (at ambient temperature) is up to 1.50 mol·dm–3 for both NH4Cl and NH4NO3. The solubility of CaSO4·2H2O was found to increase sharply with either NH4Cl or NH4NO3 concentration, whereas the temperature has a limited effect. The XRD analysis of equilibrated solids for these systems shows that CaSO4·2H2O is stable in all cases over the temperature range (298.15 to 343.15) K. The electrolyte nonrandom two-liquid (the electrolyte NRTL) model embedded in AspenPlus was applied to model the solubility of CaSO4·2H2O in the above systems. The newly obtained model parameters were used to well estimate the solubility of CaSO4·2H2O in all cases with a relative deviation of 1.52 %.

The metastable zone widths (MZWs) of triethanolamine hydrochloride ([HTEA]Cl), defined as the maximum temperature difference ΔTmax a solution can withstand before crystallization of a solid phase, in water, ethanol−water, and HCl−water mixed solvents have been determined at a saturation temperature T0 range from 293.15 to 303.15 K with cooling rate R from 3 to 8 K·h−1. Solubilities of [HTEA]Cl in ethanol−water mixtures have also been obtained using a dynamic method. An equation of MZW with similar form to Sangwal’s equation was derived from the fundamental driving force of crystallization based on chemical potential. With the newly obtained equation, the experimental values of MZW ΔTmax for [HTEA]Cl−water system at 298.15 K was correlated with the cooling rate R by ln(ΔTmax/T0) = −6.140 + 1.222 ln R. The enthalpy of mixing ΔHmix was calculated with the solubility data, and the result of differential scanning calorimetry (DSC). For [HTEA]Cl−water system, the value of −ΔHmix was determined to be 30.88 kJ·mol−1, and the addition of both HCl and ethanol led to a decrease of −ΔHmix. The experimental results also showed that MZW could be greatly enhanced when ethanol and HCl were added. It was found that the values of MZW decrease with −ΔHmix for both [HTEA]Cl−ethanol−water and [HTEA]Cl−HCl−water systems at the same saturation temperature and cooling rate.

The study of the solid–liquid phase equilibrium for the [HAE]Cl–MgCl2–H2O system is of significance for the preparation of anhydrous magnesium chloride using the thermal decomposition of the complex ([HAE]Cl·MgCl2·6H2O), which is synthesized by the reaction of aniline hydrochloride ([HAE]Cl) and bischofite (MgCl2·6H2O). In this study, a rigorous and thermodynamically consistent representation for the [HAE]Cl–MgCl2–H2O system was developed on the basis of the electrolyte nonrandom two-liquid (ENRTL) activity coefficient model embedded in Aspen Plus. The solubility of [HAE]Cl in water and magnesium chloride solutions over the temperature range from 277 to 370 K was measured by use of the dynamic method. With the equilibrium constant of [HAE]Cl obtained using experimental solubility of [HAE]Cl in water and the phase equilibrium equation, the new ENRTL parameters were obtained by regressing the solubility data for the two binary systems [HAE]Cl–H2O and MgCl2–H2O and the one ternary system [HAE]Cl–MgCl2–H2O at MgCl2 concentrations of 0.51 and 2.17 mol·kg–1. These obtained parameters could accurately predict the solubility for the ternary [HAE]Cl–MgCl2–H2O system at MgCl2 concentrations of 1.05, 1.56, 2.72, 3.21, 3.87, 4.32, and 5.05 mol·kg–1. The values at multiple saturated points at 298.15 and 323.15 K were accurately predicted with help of the newly developed model. The behavior of the ternary [HAE]Cl–MgCl2–H2O system at the two temperatures are successfully visualized with lucidity on an equilateral triangle. All of these will provide a thermodynamic basis for the preparation of the [HAE]Cl·MgCl2·6H2O complex.

A new chemical model of supersaturation (S) was developed and applied to test for the precipitation of hydromagnesite [Mg5(CO3)4(OH)2·4H2O] in the MgCl2−Na2CO3 system in supersaturated solutions over the temperature range of 50−90 °C. Based on the new model with the help of the OLI platform, the contour supersaturation of Mg5(CO3)4(OH)2·4H2O has been exactly constructed by calculating the activity coefficients of species in unstable solutions. Mg5(CO3)4(OH)2·4H2O crystals were identified using X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) images. It was found that the crystal properties, such as morphology, particle size distribution, filtration, and sedimentation characteristics, can be optimized by controlling the supersaturation during precipitation. With the control of supersaturation, well-developed spherical-like Mg5(CO3)4(OH)2·4H2O crystals can grow to an average size of 30−40 μm, indicating a narrow particle size distribution, good filtration characteristics, and a high sedimentation rate. In addition, the Mg5(CO3)4(OH)2·4H2O obtained was calcined to produce high-purity MgO at 800 °C. The size and morphology of MgO were similar to the same characteristics of the corresponding precursors.

A chemical model for the solubility of Friedel’s salt (FS, 3CaO·Al2O3·CaCl2·10H2O) was developed. The model was built with the help of the OLI platform via regression of experimental solubility data for FS in the Na−OH−Cl−NO3−H2O systems. The solubility of FS in water was measured using a batch nickel autoclave over the temperature range of 20−200 °C, and the solubility product of FS (log10 Ksp) was obtained. It was found that the solubility of FS in water shows a maximum value as a function of temperature. The solubility of FS in 0−5 mol/L NaOH and 0−2.5 mol/L NaCl solutions was found to decrease with increasing NaOH and NaCl concentrations, because of the common ion effect; however, in 0−2.5 mol/L NaNO3 solutions, it was found to increase because of complexation. During the regression analysis, it was found that CaOH+ plays an important role in solubility modeling, and its dissociation constant was determined by an empirical equation. New Bromley−Zemaitis activity coefficient model parameters for the Ca2+−OH−, CaOH+−OH−, and CaCl+−OH− ion pairs were also regressed, using the experimental solubility data generated in the present study. The new model was shown to successfully predict the solubility of FS in mixed NaOH + NaNO3 solutions not used in model parametrization. With the aid of the newly developed model, the concentration and temperature effects on calcium species distribution were analyzed.

The solubility of calcium sulfate dihydrate (CaSO4·2H2O) and calcium hydroxide (Ca(OH)2) in alkali solutions is essential to understand their desilication behavior from Bayer liquor. In this work, solubilities of calcium sulfate dihydrate and calcium hydroxide for the ternary systems of CaSO4·2H2O–NaOH–H2O, CaSO4·2H2O–KOH–H2O, and Ca(OH)2–NaOH–H2O were measured by using the classic isothermal dissolution method over the temperature range of 25–75 °C. The Pitzer model embedded in Aspen Plus platform was used to model the experimental solubility data for these systems. The experimental solubility data was employed to obtain the new binary interaction parameters for Ca(OH)+–OH−, Ca(OH)+–Ca2+ and Ca(OH)+–K+, suggesting that the species Ca(OH)+ is a dominant species in simulated solubility for alkali systems. Validation of the parameters was performed by predicting the solubility for the ternary systems of Ca(OH)2–NaOH–H2O, CaSO4·2H2O–NaOH–H2O and CaSO4·2H2O–KOH–H2O with the overall average relatively deviation (ARD) of 2.12%, 0.75% and 1.63%, respectively.

The (solid + liquid) phase equilibria of triethanolamine hydrochloride ([HTEA]Cl) ionic liquid and aqueous hydrochloric acid solutions with concentrations from (0 to 8.37) mol·kg−1 were determined by a dynamic method within the temperature range of (285.70 to 344.65) K. Solubilities of [HTEA]Cl were found to increase with increasing temperature for all the investigated solutions. However, solubilities of [HTEA]Cl in aqueous hydrochloric acid decrease with the increment of the concentration of the acid due to the common ion effect. KSP values of [HTEA]Cl were obtained by use of the solubility data of [HTEA]Cl in water. The modified Apelblat equation was used successfully to correlate experimental data of solubilities in hydrochloric acid. Molar dissolution enthalpy ΔHSol of [HTEA]Cl in hydrochloric acid solutions was determined with the newly obtained Apelblat equation parameters.

This work presents vapor pressure data for water, 1-propanol, and 2-propanol as well as their binary mixtures in the presence of ionic liquid (IL) 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) at different temperatures and IL content ranging from mass fraction 0.10 to 0.70 using a quasi-static ebulliometer method. Activity coefficients of these solvents in the IL have been determined from the vapor pressure data of binary systems and correlated by the nonrandom two-liquid (NRTL) equation with an average relative deviation (ARD) within 0.013. The resulting binary NRTL parameters were used for the prediction of vapor pressure of ternary systems with fair accuracy. Furthermore, the isobaric vapor−liquid equilibrium data for ternary systems water + 1-propanol + [MMIM][DMP] and water + 2-propanol + [MMIM][DMP] at different IL mass fractions were predicted. It is shown that the relative volatility of 1-propanol and 2-propanol is enhanced and that the azeotrope of water + 1-propanol and water + 2-propanol mixtures is eliminated completely.

The solubility and stability of nesquehonite (MgCO3·3H2O) in mixed solutions (NaCl + MgCl2, NH4Cl + MgCl2, LiCl, and LiCl + MgCl2) were measured by using a classic isothermal dissolution method over the temperature range of (298 to 308) K. The concentration investigated for all salts was up to 0.2 mol·dm−3 NaCl, 1.5 mol·dm−3 NH4Cl, 0.6 mol·dm−3 MgCl2, and 1.5 mol·dm−3 LiCl at ambient temperature. The solubility of MgCO3·3H2O phases in all the cases investigated was found to increase with the temperature increment. The comparison of solubility in MgCl2 solutions and NaCl + MgCl2, NH4Cl + MgCl2, and LiCl + MgCl2 mixed solutions has been investigated. XRD and SEM examination of the equilibrated solids showed that nesquehonite in all cases is stable in the temperature range of (298 to 308) K.

This work reports the stability and solubility of nesquehonite in several salts (NaCl, NH4Cl, MgCl2, and KCl) over the temperature range of (15 to 35) °C. The needle-like nesquehonite used in this work was prepared by the reaction of analytical pure MgCl2 with Na2CO3. The concentration investigated for all salts was up to 4 mol·dm−3 NaCl, 3.5 mol·dm−3 NH4Cl, 4 mol·dm−3 MgCl2, and 1.0 mol·dm−3 KCl at ambient temperature. The solubility of nesquehonite in pure water was found to decrease with temperature within the temperature range in which nesquehonite is the stable phase. In NaCl solutions, the solubility of nesquehonite initially increases to a maximum value and then decreases gradually with an increase of the common salt concentration. It was further found that the addition of MgCl2, NH4Cl, or KCl causes the solubility of nesquehonite to increase due apparently to complexation. XRD and SEM examination of the equilibrated solids showed that nesquehonite is stable in pure water up to 50 °C, but its stability region becomes smaller in concentrated brines.

The nucleation of nesquehonite (MgCO3·3H2O) in MgCl2−Na2CO3 system with and without the addition of NaCl was studied within a supersaturation range of 1.06–1.48 at 288.15–308.15 K. The supersaturation (S) of MgCO3·3H2O was exactly calculated by aqueous (H+ ion) model through OLI platform. The conductivity method was applied in this experiment to determine the induction period of MgCO3·3H2O. The effects of temperature, supersaturation, and presence of additive (NaCl) on the induction period of MgCO3·3H2O were studied experimentally. As expected from theory, it was found that the induction period decreases when either temperature or supersaturation increases. The induction period was prolonged by adding NaCl in solutions at a constant supersaturation. From the dependence of the induction period on temperature and supersaturation, it was possible to distinguish between the homogeneous and heterogeneous nucleation mechanisms. At last, the activation energy (Eact) for MgCO3·3H2O crystallization and the interfacial tension between MgCO3·3H2O and aqueous solutions of homogeneous (γS,hom) and heterogeneous (γS,het) nucleation were calculated from measurements of the induction period for the MgCO3·3H2O nucleation with and without the addition of NaCl.