Univariant Curves Research Articles

Phase Equilibria in the Aqueous Ternary System (LiBO2 + CaB2O4 + H2O) at 288.15 and 298.15 K

The solubilities and physicochemical properties, including density and pH, in the ternary system (LiBO2 + CaB2O4 + H2O) at (288.15 and 298.15) K were investigated using the isothermal dissolution equilibrium method. According to the experimental results of the ternary system at (288.15 and 298.15) K, the stable phase diagrams and the diagrams of physicochemical properties were plotted versus composition. In the phase diagrams of the ternary system at (288.15 and 298.15) K, there is one invariant point (LiBO2·8H2O + CaB2O4·6H2O), two univariant isotherm dissolution curves, and two crystallization regions corresponding to lithium metaborate octahydrate (LiBO2·8H2O) and calcium metaborate hexahydrate (CaB2O4·6H2O), respectively. This system at both temperatures belongs to hydrate type I classification and neither double salt nor solid solution were found. A comparison of the phase diagrams for the ternary system at (288.15 and 298.15) K shows that the numbers of solid phase and the minerals present are the same; the crystallized area of CaB2O4·6H2O increased at the higher temperature, while that of LiBO2·8H2O decreased. The physicochemical properties (density and pH values) of the ternary system at the two temperatures change regularly with increasing lithium metaborate concentration. The calculated values of density using empirical equations of the ternary system are in good agreement with the experimental values.

Solid–liquid equilibria in the quaternary system Na+, NH4+//Cl−, H2PO4−–H2O at 298.15 K and 323.15 K

The phase equilibrium of the quaternary system Na+, NH4+//Cl−, H2PO4−–H2O at 298.15K and 323.15K is investigated by the isothermal solution saturation method. The densities of the saturation solution were obtained. The phase diagrams, water content diagrams and density–composition diagrams were constructed. The phase diagrams of the system contain four ternary invariant points, two quaternary invariant points, five univariant curves and four crystallization regions corresponding to NaCl, NH4Cl, NH4H2PO4 and NaH2PO4. NH4H2PO4 has the largest crystallization region among the four salts, indicating that NH4H2PO4 is the easiest to crystallize out. There are no double salts or solid solutions in this system. The solubilities of the saturated solutions change regularly with the changing of composition. According to the phase diagrams, the appropriate concentration of Cl− and H2PO4− for the crystallization of pure monoammonium phosphate can be obtained and the crystallization process can be planned. The solubility data, density data, phase diagrams and water content diagrams can provide fundamental basis for the crystallization process of monoammonium phosphate.

Study on the phase equilibrium of the quaternary systems Na+ (K+)//H2PO4−, Cl−, SO42−–H2O at 313.15 K

The solid–liquid equilibrium of quaternary systems (NaCl+NaH2PO4+Na2SO4+H2O) and (KH2PO4+KCl+K2SO4+H2O) at 313.15K was studied by an isothermal solution saturation method and the solubilities of salts and equilibrium solid phases in the two systems were determined. Based on the measured data, dry-salt phase diagrams and the relevant water-phase diagrams were plotted in the two systems. Experimental results indicate that there are one invariant point, three univariant curves and three fields of crystallization in the two quaternary systems. For the quaternary system (NaCl+NaH2PO4+Na2SO4+H2O) at 313.15K, the composition of the solution at equilibrium corresponding to invariant point is NaH2PO4 45.23wt%, Na2SO4 4.15wt%, NaCl 6.54wt%. Three isotherm curves represent the cosaturated process of two salts (NaCl+Na2SO4), (NaH2PO4·2H2O+NaCl) and (NaH2PO4·2H2O+Na2SO4). For the quaternary system (KH2PO4+KCl+K2SO4+H2O) at 313.15K, invariant point is saturated with the three salts (KCl+K2SO4+KH2PO4) and the composition of the corresponding liquid phase is w (KCl)=25.39wt%, w (K2SO4)=1.42wt%, w (KH2PO4)=4.38wt%. Three isotherm curves represent the cosaturated process of two salts (KCl+K2SO4), (KCl+KH2PO4) and (K2SO4+KH2PO4). Neither complex salt nor solid solution is found in the two systems at 313.15K. The physicochemical properties (nD, η, ρ, pH) of equilibrium quaternary system changed regularly with the concentration change of the liquid phase. All results obtained in this experiment can be used for the solvent extraction process of KH2PO4 in the industrial production and further theoretical studies.

Stable (solid + liquid) phase equilibrium for the ternary systems (K2SO4 + KH2PO4 + H2O), (K2SO4 + KCl + H2O) at T = 313.15 K

The stable (solid+liquid) phase equilibria and physico-chemical properties of the solution in the ternary systems (K2SO4+KH2PO4+H2O) and (K2SO4+KCl+H2O) at T=313.15K were determined by using an isothermal solution saturation method. According to the experimental data, the phase diagrams and the diagrams of physico-chemical properties versus composition were plotted. It was found that there were one invariant point, two univariant curves and three fields of crystallization in the ternary systems (K2SO4+KH2PO4+H2O) and (K2SO4+KCl+H2O) at T=313.15K. On the basis of the phase diagrams obtained, we analyzed each invariant point. When K2SO4 and KH2PO4 were analyzed as (7.71, 20.99)wt%, respectively, the ternary system (K2SO4+KH2PO4+H2O) reached saturation at T=313.15K. When K2SO4 and KCl were analyzed as (1.15, 27.08)wt%, respectively, the ternary system (K2SO4+KCl+H2O) reached saturation at T=313.15K. The solubility of K2SO4 is the lowest among the three salts, and the crystalline fields of K2SO4 in the two ternary systems are larger than that of KH2PO4 and KCl, which shows that K2SO4 can be easily separated from the mixed aqueous solution. Thus, knowledge of (solid+liquid) equilibrium, especially the crystalline fields at T=313.15K, would be extremely valuable to design and optimize solvent extraction process of KH2PO4 and other crystallization processes involving the two ternary systems in the industrial production.

Solid–liquid metastable phase equilibria for the ternary system (Li2SO4 + K2SO4 + H2O) at 288.15 and 323.15 K, p = 0.1 MPa

Metastable solubilities and physicochemical properties including density and refractive index of the aqueous ternary system (Li2SO4+K2SO4+H2O) at 288.15 and 323.15K and p=0.1MPa were determined with the isothermal evaporation method. On the basis of experimental data, the metastable phase diagrams and the diagram of physicochemical properties versus composition in the ternary system at 288.15 and 323.15K were plotted. In the metastable phase diagrams of this ternary system at 288.15 and 323.15K, in all there are two invariant points, three univariant solubility curves, and three metastable crystallization regions, corresponding to lithium sulfate monohydrate (Ls, Li2SO4·H2O), double salt (Db, K2SO4·Li2SO4) and arcanite (Ar, K2SO4). The hydrates in this system at both temperatures belong to a hydrate type I, and the double salt (K2SO4·Li2SO4) belongs to incongruent at 288.15K and congruent double salt at 308.15K, respectively. A comparison of the metastable phase diagrams at 288.15 and 323.15K shows that the area of Ar is decreased obviously whereas the areas of Db and Ls are increased with the increasing of temperature, and no solid solutions were found. The density and refractive index in the metastable ternary system at 288.15 and 323.15K change regularly with the mass fraction of potassium sulfate concentration and reach the extreme values at the invariant points. The densities and refractive indices were correlated with empirical equations, and the calculated values at two temperatures agree well with the experimental results.

Solid–Liquid Equilibria in the Ternary Systems NaCl–SrCl2–H2O and KCl–SrCl2–H2O at 348 K

Solid–liquid equilibria in the ternary systems NaCl–SrCl2–H2O and KCl–SrCl2–H2O at 348 K were measured by the isothermal solution saturation method. The composition of the equilibrium solid phase, solubilities of salts, and densities of saturated solution in the two systems were determined. Phase diagrams of ternary systems were plotted according to experimental data. They both contained one invariant point, two univariant curves, and two regions of crystallization. Respectively, univariant curves of the corresponding equilibrium solid phase were sodium chloride (NaCl) and strontium chloride dihydrate (SrCl2·2H2O) in the ternary system NaCl–SrCl2–H2O, and potassium chloride (KCl) and strontium chloride dihydrate (SrCl2·2H2O) in the ternary system KCl–SrCl2–H2O. The two ternary systems belong to the simple type, and neither double salts nor solid solution was found. The density transformation rules were simply discussed. Simultaneously, the solubilities and density data were compared with the experimental ...

Measurements and calculations of solid–liquid equilibria in the quaternary system NaBr–KBr–CaBr2–H2O at 298 K

The solubilities and densities of the quaternary system NaBr–KBr–CaBr2–H2O were investigated by the method of isothermal solution saturation at 298K. On the basis of the experimental data, the phase diagram, water content diagram and the density-composition diagram were plotted, respectively. In the phase diagram of quaternary system NaBr–KBr–CaBr2–H2O at 298K, no complex salt or solid solution was found. There are two invariant points, five univariant curves, and four crystallization fields corresponding to NaBr, NaBr·2H2O, KBr and CaBr2·6H2O. Pitzer's equations based model has been applied to calculate bromide minerals solubilities in the quaternary system NaBr–KBr–CaBr2–H2O at 298K. All binary and mixing ion interaction parameters and solubility products of bromide solids are taken from previously published T-variation model for the system under study, adapted to 298K. The predicted and experimental solubilities are in a very good agreement up to a very high total concentration of the quaternary system.

Measurement and Application of a Solid–Liquid Equilibrium for the Ternary NaCl + Na2S2O3 + H2O System

Solid–liquid equilibrium data for the NaCl + Na2S2O3 + H2O system at 283.15 and 303.15 K were measured using the method of isothermal solution saturation combined with a moist residue method of Schreinemaker, the equilibrium solid phase was identified by powder X-ray diffraction, and finally the solid–liquid phase diagrams of the ternary system were constructed. The ternary NaCl + Na2S2O3 + H2O phase diagrams at 283.15 and 303.15 K turned out to be of the simple eutectic type. One invariant point, two univariant curves, and two crystallization regions exist in each of the phase diagrams. The crystallization region of NaCl is larger than that of Na2S2O3·5H2O at 283.15 K, and the crystallization region of NaCl expands while that of Na2S2O3·5H2O decreases when the temperature rises to 303.15 K. Consequently, the invariant point at 303.15 K is located in the Na2S2O3·5H2O single-salt crystallization region of the phase diagram at 283.15 K. On the basis of this thermodynamic characteristic, a method for separation of the NaCl + Na2S2O3 mixture was proposed, from which both of the pure salts could be obtained.

Stable phase equilibria in the ternary system (Na2SO4 + Li2SO4 + H2O) at 308.15 K and 313.15 K

Phase equilibrium data in the ternary system (Na2SO4+Li2SO4+H2O) at 308.15K and 313.15K were measured using the isothermal dissolution method, and the corresponding stable phase diagrams were plotted. The results showed that there were three invariant points, four univariant curves and four crystallization regions: Li2SO4·H2O (Ls), LiNa(SO4) (Db1), Na3Li(SO4)2·6H2O (Db2), and Na2SO4 (Th); and no solid solution was found in the ternary system at 308.15K and 313.15K. A comparison of the stable phase diagrams for the ternary system at different temperature indicates that the areas of the crystallization regions of Th and Db1 are increased with the increase of temperature, and the one belonging to Db2 is disappeared along with the increase of temperature.

Solid–Liquid Equilibria in the Ternary Systems KBr–CaBr2–H2O and NaBr–CaBr2–H2O at 348 K

The solubilities of salts and densities of equilibrium solution in the ternary systems KBr–CaBr2–H2O and NaBr–CaBr2–H2O at 348 K were determined with the method of isothermal solution saturation. On the basis of the experimental data, equilibrium phase diagrams in the ternary systems listed above were plotted, respectively. The solubility diagram of the ternary system KBr–CaBr2–H2O has one invariant point, two stable solubility isotherm curves, and two crystallization fields corresponding to CaBr2·2H2O and KBr. The solubility diagram of the ternary system NaBr–CaBr2–H2O includes one invariant point, two univariant curves and two fields of crystallization CaBr2·2H2O and NaBr. And the densities calculated from empirical equations are in good agreement with the experimental data. The dissolution equilibrium constant K for NaBr, KBr, CaBr2·2H2O in the ternary systems at 348 K were fitted by using the Pitzer equations and the multiple linear regression method. A chemical model was constructed to calculate the ...

Solid–liquid equilibrium of quaternary system Na+//H2PO4−, Cl−, SO42−–H2O at 298.15 K

The sodium dihydrogen phosphate is one important chemical product, which has the widespread application in medicine, food, chemical industry, water treatment, agriculture aspects and so on. The solid–liquid phase equilibrium and physic-chemical properties of the quaternary system Na+//H2PO4−, Cl−, SO42−–H2O at 298.15K were obtained by means of an isothermal solution method. There are four crystallization regions, one invariant point, and four univariant curves in the system. The crystallization region of NaH2PO4·2H2O (II) is the smallest, and its solubility is the biggest, which indicated that NaH2PO4·2H2O has a strong salt-out effect on Na2SO4·10H2O, Na2SO4 and NaCl. The physic-chemical properties (refractive index, conductivity, pH values, density and viscosity) of solution changed regularly with the increasing mass fraction of NaH2PO4. All results obtained in this experiment can be used for the solvent extraction process of NaH2PO4 in the industrial production and further theoretical studies.

Phase equilibria in the ternary systems KBr–MgBr2–H2O and NaBr–MgBr2–H2O at 348.15 K

Solid–liquid equilibria in the ternary systems KBr–MgBr2–H2O and NaBr–MgBr2–H2O at 348.15K were determined with the method of isothermal solution saturation. Also determined are the densities of saturated solutions. According to the experimental data, the equilibrium phase diagrams of the two ternary systems were plotted. The phase diagram of first system has two invariant points, three univariant curves and three crystallization fields (which are saturated with respect to MgBr2·6H2O, KBr·MgBr2·6H2O and KBr, respectively, where KBr·MgBr2·6H2O is an incongruent double salt). The phase diagram of the second system has one invariant point, two univariant curves and two crystallization fields (which are saturated with respect to MgBr2·6H2O and NaBr, respectively). The dissolution equilibrium constant of NaBr, KBr, MgBr2·6H2O and KBr·MgBr2·6H2O at 348.15K were fitted with Pitzer equations. A chemical model based on Pitzer equations was constructed to calculate the solubilities of salts in the two systems at 348.15K. The calculated solubilities are in agreement with experimental results.

Phase equilibria in the ternary system (LiCl + Li2SO4 + H2O) at T = 308.15 K and p = 0.1 MPa: Experimental data and predictions using the Pitzer model

The solubilities and the physicochemical properties including density, viscosity, refractive index, conductivity, and pH of the aqueous ternary system (LiCl+Li2SO4+H2O) at T=308.15K and p=0.1MPa were determined using the isothermal evaporation method, and the metastable phase diagram and the physicochemical property diagram versus composition of liquid phase solution for the system at 308.15K were plotted. In the metastable phase diagram of the ternary system at 308.15K, there is one invariant point, two univariant curves, and three crystallization zones corresponding to lithium sulfate monohydrate (Li2SO4·H2O), lithium chloride monohydrate (LiCl·H2O) and (Li2SO4·H2O+LiCl·H2O). It belongs to the hydrate type I, and neither double salts nor solid solution were found. On the basis of Pitzer ion-interaction theory of the electrolytes and the chemical equilibrium HMW model, Pitzer single-salt parameter of lithium chloride at 308.15K was fitted, and the single-salt parameters of lithium sulfate, mixing ion-pair θCl,SO4, and the Debye–Hückel limiting slope AΦ at 308.15K were obtained according to the temperature-dependent equation of parameters presented in the literatures. And then, the solubilities on the ternary system (LiCl+Li2SO4+H2O) at 308.15K were calculated. A comparison shows that the calculated solubility agrees well with the experimental data.

Thermodynamics Phase Equilibria of the Aqueous Ternary Systems LiCl + KCl (MgCl2) + H2O at 348 K

The thermodynamics phase equilibria of the aqueous ternary systems LiCl + MgCl2 + H2O and LiCl + KCl + H2O at 348 K were investigated using an isothermal evaporation method. The solubilities and physicochemical properties such as density and refractive index of the equilibrated solution were determined. The compositions of solid phases were confirmed using the Scherinemakers’ wet residue method. In accordance with the experimental data, the phase diagrams and physicochemical vs composition diagrams were constructed. The ternary system LiCl + MgCl2 + H2O is of a complex type with double salt LiCl·MgCl2·7H2O (lithium carnallite) formed at 348 K, and its phase diagram consists of two invariant points, three univariant curves, and three crystallization fields corresponding to lithium chloride monohydrate (LiCl·H2O), magnesium chloride hexahydrate (MgCl2·6H2O), and lithium carnallite (LiCl·MgCl2·7H2O). The ternary system LiCl + KCl + H2O is of a simple eutectic type at 348 K, and its phase diagram is composed of one invariant point, two univariant curves and two crystallization fields corresponding to potassium chloride (KCl) and lithium chloride monohydrate (LiCl·H2O). Lithium chloride has a salting out effect on magnesium chloride or potassium chloride. Comparisons between the metastable and stable phase diagrams at 348 K of these two ternary systems have been drawn. In the system LiCl + MgCl2 + H2O, the crystallization region of MgCl2·6H2O under the metastable equilibrium is smaller, while the crystallization region of the LiCl·MgCl2·7H2O is larger. In the system LiCl + KCl + H2O, the crystallization regions of LiCl·H2O and KCl under metastable equilibrium are both smaller. Comparisons between the metastable phase diagrams of system LiCl + KCl + H2O at (298, 323, and 348) K show that the crystallization region of LiCl·H2O increased with the rise of temperature, whereas the crystallization region of salt KCl is decreased.

Experimental determination and modeling of the solubility phase diagram of the ternary system (Li2SO4 + K2SO4 + H2O) at 288.15 K

The solubility and density in the thermodynamic phase equilibria ternary system (Li2SO4+K2SO4+H2O) at 288.15K and 0.1MPa were investigated experimentally with the method of isothermal dissolution equilibrium. This system at 288.15K consists of two invariant points, three univariant isothermal dissolution curves; and three crystallization regions. The salt Li2SO4·K2SO4 belongs to the incongruent double salt, and no solid solution was found. Based on the Pitzer model and its extended Harvie–Weare (HW) model, the mixing ion-interaction parameters of θLi,K, ψLi,K,SO4 at 288.15K and the solubility equilibrium constants Ksp of solid phases Li2SO4·H2O and Li2SO4·K2SO4, which are not reported in the literature were acquired. A comparison between the calculated and experimental results at 288.15K for the ternary system shows that the calculated solubilities obtained with the extended HW model agree well with experimental data.

Solid–Liquid Stable Equilibrium of the Aqueous Quaternary System NH4SCN–(NH4)2S2O3–(NH4)2SO4–H2O at 303.15 K

The salts of thiocyanate, thiosulfate, and sulfate exist in a variety of industrial processes such as textile, coking, and electroplating. The effluents from these industries cannot be discharged directly owing to their severe environmental pollution. In addition, there is an opportunity to recover significant commercial value from these effluents. The phase equilibria and phase diagram play a major role in separating and recovering useful resources. In this paper, the phase diagrams of the system NH4SCN–(NH4)2S2O3–(NH4)2SO4–H2O and its subsystems at 303.15 K were determined by an isothermal dissolution equilibrium method. In the phase diagram of the quaternary system, there is one invariant point, three univariant curves and three crystallized regions. The invariant point is cosaturated with ammonium thiocyanate, ammonium sulfate, and ammonium thiosulfate (NH4SCN + (NH4)2SO4 + (NH4)2S2O3). The three crystallization regions correspond to ammonium sulfate ((NH4)2SO4), ammonium thiocyanate (NH4SCN), and ammonium thiosulfate ((NH4)2S2O3). The first one is the largest area, but the latter two are much smaller ones. The phase diagram can be utilized to separate and recover NH4SCN, (NH4)2SO4, and (NH4)2S2O3 selectively and individually from the desulfurization effluents. The result of this paper shows that the environmental pollutant can be converted to the valuable product by a simple, economical, and green process.

Solid–liquid equilibria in the quinary system LiCl–KCl–RbCl–MgCl2–H2O at T = 323 K

The mixed aqueous electrolyte system containing the chlorides of lithium, potassium, rubidium, and magnesium has been investigated using the method of isothermal evaporation at 323K. The space diagram, the planar projection diagram and the water content diagram have been constructed based on the Jänecke method. There are six invariant points, eighteen univariant curves, and eight crystallization fields corresponding to single salts lithium chloride monohydrate (LiCl·H2O), bischofite (MgCl2·6H2O), a solid solution of potassium and rubidium chloride [(K,Rb)Cl], and carnallite type double salts LiCl·MgCl2·7H2O, KCl·MgCl2·6H2O, and RbCl·MgCl2·6H2O in the space diagram. With a view to the crystallization zones, the crystallization zone of salt [(K,Rb)Cl] occupies the largest part, meaning [(K,Rb)Cl] can be more easily separated from solution than the other coexisting salts in this system at 323K.

Stable Phase Equilibrium of Aqueous Quaternary System Li+, K+, Mg2+//Borate–H2O at 348 K

The solubility values and physicochemical properties such as densities, refractive indices, and pH values of the equilibrium solution in the quaternary system Li+, K+, Mg2+//borate–H2O at 348 K were measured by isothermal dissolution method. The phase diagram, water content diagram, and the diagrams of the physicochemical properties versus composition were constructed using the measured data. Results show that this quaternary system at 348 K is of a simple type, no double salt or solid solution formed. The stable phase diagram of this quaternary system consists of one invariant point, three univariant curves, and three crystalline phase areas. The invariant point saturated with three salts corresponding to lithium tetraborate trihydrate (Li2B4O7·3H2O), potassium tetraborate tetrahydrate (K2B4O7·4H2O), and hungchaoite (MgB4O7·9H2O). The crystallization field of MgB4O7·9H2O is the maximum, meaning that the salt magnesium borate has the smallest solubility among the coexisting salts. Comparisons between the stable phase diagrams at 288 K and 348 K show that the crystallization zones of MgB4O7·9H2O decreased at 348 K, while the crystallization zones of K2B4O7·4H2O and Li2B4O7·3H2O both enlarged at 348 K. On the univariant curve CE, the water contents decrease with the increase of J(K2B4O7); the densities and refractive indices both increase with the increase of J(K2B4O7) and reach the maximum at invariant point E.

Measurement and Thermodynamic Modeling Study on the Solid and Liquid Equilibrium of Ternary System NaBr–CaBr2–H2O at 288.15 K

The solubilities and refractive indices of the NaBr–CaBr2–H2O system at 288.15 K were determined using the isothermal equilibrium solution method. The phase diagram and refractive index diagram were drawn for this system at 288.15 K. The system belongs to the hydrate II type. The phase diagram is comprised of two invariant solubility points, three univariant solubility curves, and three areas of crystallization: NaBr·2H2O, NaBr and CaBr2·6H2O. Using the temperature-dependent formulas from the literature, the Pitzer parameters and the solubility product constants (ln Ksp) of NaBr·2H2O and NaBr were determined. Applying the Pitzer and Harvie–Weare (HW) model, the solubility product constant of CaBr2·6H2O was fit with the solubilities in this research work, and then, the mean activity coefficients of sodium bromide and calcium bromide and the solubilities for the ternary system at 288.15 K were demonstrated. Comparisons between the calculated and measured solubilities show that the predicted data have good accordance with the experimental results.

Solid-liquid equilibria in the quaternary system Na+, K+//Br−, B4O7 2−-H2O at 298 K

According to the compositions of the underground gasfield brines in the west of Sichuan Basin, the solubilities and densities of the solid-liquid equilibria in the quaternary system Na+, K+//Br−, B4O72−-H2O at 298 K were determined by the method of isothermal solution saturation. From the experimental data, the phase diagram, water content diagram and density-composition diagram were obtained. This quaternary system is of simple eutectic type, without double salt and solid solution. There are two invariant points, five univariant curves, four fields of crystallization in the system. The equilibrium solid phases are Na2B4O7·10H2O, K2B4O7·4H2O, NaBr·2H2O and KBr. Na2B4O7·10H2O has a larger crystallization field, and NaBr·2H2O has a smaller crystallization field. It is also found that bromide has the salting-out effect on borate in the quaternary system Na+, K+//Br−, B4O72−-H2O at 298 K.