Based on the requirement for the comprehensive exploitation and utilization of the salt lake resources magnesium chloride and potassium chloride, a new technology to produce KCl and ammonium carnallite (NH4Cl·MgCl2·6H2O) by using NH4Cl as salting-out agent to separate carnallite is proposed. The solubilities of quaternary system KCl–MgCl2–NH4Cl–H2O were measured by the isothermal method at t = 60.00 °C and the corresponding phase diagram was plotted and analyzed. The analysis of this phase diagram shows that there are seven saturation points and eight regions of crystallization. These eight regions of crystallization represent salts corresponding to KCl, NH4Cl, MgCl2·6H2O, (K1−n(NH4)n)Cl, ((NH4)nK1−n)Cl, (K1−n(NH4)n)Cl·MgCl2·6H2O, KCl·MgCl2·6H2O and NH4Cl·MgCl2·6H2O. According to the phase diagram analysis and calculations, ammonium carnallite (NH4Cl·MgCl2·6H2O) and KCl can be obtained using carnallite as raw materials and ammonium chloride as salting-out agent at t = 60.00 °C. The new technology shows the advantages of being easy to operate and having low energy consumption. The research on this quaternary phase diagram is the foundation for reasonable development of carnallite resources and comprehensive utilization of the salt lake brines.

•Subsystems of (NH4)2SO4-CO(NH2)2-MgSO4-H2O at 0 °C were determined.•Phase diagrams of (NH4)2SO4-CO(NH2)2-MgSO4-H2O at 0 °C and 25 °C were constructed.•Phase diagrams of the quaternary system at the two temperatures were compared.•A new technology to separate CO(NH2)2 and (NH4)2SO4 from urea waste water was exhibited.Solubilities of the quaternary system CO(NH2)2-MgSO4-(NH4)2SO4-H2O at 0 °C and 25 °C were studied by isothermal solution saturation method. Under the experimental data, phase diagrams were constructed. This quaternary system at 25 °C contains five crystallization regions corresponding to MgSO4·7H2O, MgSO4·(NH4)2SO4·6H2O, CO(NH2)2, (NH4)2SO4 and MgSO4·CO(NH2)2·2H2O. Compared with the phase diagram at 25 °C, there was no crystallization region of MgSO4·CO(NH2)2·2H2O in the phase diagram at 0 °C·MgSO4·(NH4)2SO4·6H2O has the largest crystallization area among the salts, indicating MgSO4·(NH4)2SO4·6H2O is the easiest to crystallize out. Based on the characteristic of the phase diagrams, a new technology to separate (NH4)2SO4 and CO(NH2)2 from urea waste water is proposed. This process shows the advantages of recovering desirable substances and making urea waste water discharged up to standard.

•Determination of the phase equilibrium of K2SO4–MgSO4–(NH4)2SO4–H2O system at 25 °C.•Dry salt phase diagram of this system was investigated and analyzed.•A new K–Mg–N compound fertilizers was generated.•Calculation of the phase equilibrium of the above system by Pitzer model.•The calculated results are consistent with the experimental data well.The solubilities of the quaternary system K2SO4–MgSO4–(NH4)2SO4–H2O were measured by isothermal method at 25 °C and their dry salt phase diagrams were plotted. The results indicated that, at 25 °C, the solubility phase diagram of this quaternary system consists of seven crystallization regions, those are single-salt crystallization region MgSO4·7H2O, (NH4)2SO4, and K2SO4, complex salt crystallization region MgSO4·(NH4)2SO4·6H2O, MgSO4·K2SO4·6H2O, solid solution crystallization region (K1−n, NH4n)2SO4 (n:0.143–0.893) and (K1−n, NH4n)2SO4·MgSO4·6H2O (n:0.552–0.973), respectively. The extended Pitzer model was derived and applied to the phase equilibrium calculation of system K2SO4–MgSO4–(NH4)2SO4–H2O and its sub-systems at 25 °C. The results showed that the calculated values were consistent with experimental results well. The study on the quaternary system K2SO4–MgSO4–(NH4)2SO4–H2O provides a foundation for the N–Mg–K–S compound fertilizers preparation.

•Determination of phase equilibrium of Mg2+, NH4+NH4+//Cl−, SO42−SO42−–H2O system at 0 °C.•Phase diagram of this system has been investigated and analyzed.•A new technology to produce Mg–N compound fertilizers has been proposed.•Calculation of the phase equilibrium concerning this system by Pitzer model.•Consistence between calculated results and experimental data has been presented.In order to improve the technology for producing Mg–N compound fertilizer and NH4Cl based upon the analysis of phase diagram of Mg2+, NH4+NH4+//Cl−, SO42−SO42−–H2O system at 25 °C, the phase equilibrium of this quaternary system at 0 °C was studied. The solubilities of the quaternary system Mg2+, NH4+NH4+//Cl−, SO42−SO42−–H2O at 0 °C were measured by isothermal method, and the corresponding phase diagram was plotted. In this phase diagram, there are six solid phase crystalline zones, which correspond to MgCl2·6H2O, NH4Cl, MgCl2·NH4Cl·6H2O (NH4)2SO4, MgSO4·7H2O and MgSO4·(NH4)2SO4·6H2O respectively. The crystalline zones of MgSO4·(NH4)2SO4·6H2O and NH4Cl are larger than the others, which indicates that MgSO4·(NH4)2SO4·6H2O and NH4Cl can crystallize out easily. According to the analysis and calculation of the phase diagrams of Mg2+, NH4+NH4+//Cl−, SO42−SO42−–H2O system at 0 °C and 25 °C, the appropriate conditions for this technology were obtained. In the process, the Mg–N compound fertilizer can be prepared at 0 °C and the NH4Cl can crystallize out at 25 °C. The solubilities of the studied system were calculated on the basis of the extended Pitzer model, and the results showed that the calculated values agrees well with the experimental results.

On the basis of the comprehensive utilization of the Na–Mg salt deposit, a new process to produce NaCl and ammonium carnallite (MgCl2·NH4Cl·6H2O) by using NH4Cl and the solution left after the preparation of potassium salt as raw materials was proposed. For this, the phase equilibrium of the quaternary system NaCl–MgCl2–NH4Cl–H2O at 25 and 0 °C was studied. The solubilities of the quaternary system NaCl–MgCl2–NH4Cl–H2O were measured by an isothermal method, and the corresponding phase diagrams were drawn out. From the phase diagrams: there are four solid phase crystalline zones, which correspond to NaCl, MgCl2·6H2O, NH4Cl, and MgCl2·NH4Cl·6H2O respectively. NaCl and MgCl2·NH4Cl·6H2O have larger crystalline zones at 25 °C than at 0 °C, and NH4Cl has a smaller crystalline zone at 25 °C than at 0 °C. It indicates that NaCl and MgCl2·NH4Cl·6H2O are easy to crystallize out. On the basis of the analysis and calculation of the phase diagrams, the appropriate conditions for the process were identified. In the process, the NaCl could be prepared at 25 °C, and the ammonium carnallite could crystallize out at 0 °C when NH4Cl was added into the remaining solution. The solubilities of the studied system were calculated based on the extended Pitzer model, and the results showed that the calculated values were closed to the experimental results.

•Determination of the phase equilibrium of system Na2SO4–MgSO4–CO(NH2)2–H2O and its sub-systems.•Phase diagrams of these systems were investigated and analyzed.•Separation of Na2SO4 and MgSO4 by salting out method with CO(NH2)2.•Calculation of the phase equilibrium of Na2SO4–MgSO4–CO(NH2)2–H2O system by Pitzer model.The solubilities of ternary system Na2SO4–CO(NH2)2–H2O and MgSO4–CO(NH2)2–H2O and quaternary system Na2SO4–MgSO4–CO(NH2)2–H2O at 60 °C were measured by isothermal method, and the corresponding phase diagrams were studied. There are five crystalline fields in the quaternary system Na2SO4–MgSO4–CO(NH2)2–H2O at 60 °C, which correspond to MgSO4·6H2O, Na2SO4·MgSO4·4H2O, Na2SO4, CO(NH2)2 and MgSO4·CO(NH2)2·4H2O respectively. On the basis of the analyses of the phase diagram of the quaternary system Na2SO4–MgSO4–CO(NH2)2–H2O at 60 °C and 25 °C, Na2SO4 and Mg–N compound fertilizers can be produced using CO(NH2)2 as salting-out agent directly. On the basis of the extended Pitzer model of electrolyte solution theory, the solubilities of Na2SO4–MgSO4–CO(NH2)2–H2O system at 60 °C were calculated. The results showed that calculated values were well consistent with experimental results.

The solubilities of quaternary system Na2SO4–MgSO4–(NH4)2SO4–H2O at 60 °C were measured by the isothermal method, and the corresponding phase diagram was studied. The analysis of the phase diagram shows that there are five crystalline fields, MgSO4·6H2O, Na2SO4·MgSO4·4H2O, Na2SO4, (NH4)2SO4, and MgSO4·(NH4)2SO4·6H2O, respectively. MgSO4·(NH4)2SO4·6H2O, and Na2SO4 crystalline fields are larger than other crystalline fields, which indicates that MgSO4·(NH4)2SO4·6H2O and Na2SO4 are crystallized out easily. On the basis of the analysis and calculation of the phase diagrams of the quaternary system Na2SO4–MgSO4–(NH4)2SO4–H2O and ternary system Na2SO4–(NH4)2SO4–H2O at 60 °C, a technology was designed to produce Mg–N compound fertilizers and Na2SO4 using (NH4)2SO4 as a salting-out agent to separate bloedite, which is easy to operate, fast to reach phases equilibrium, and can gain anhydrous Na2SO4 directly. On the basis of the Pitzer model of electrolyte solution theory, the solubilities of Na2SO4–MgSO4–(NH4)2SO4–H2O system at 60 °C were calculated. The results showed that calculated values were well consistent with experimental results.

The solubilities of the ternary system MgSO4–(NH4)2SO4–H2O and the quaternary system Na2SO4–MgSO4–(NH4)2SO4–H2O at 0 °C were measured, and the phase diagrams of these two systems were plotted. On the basis of the phase diagrams obtained, we analyzed each saturation point and crystalline region. It indicated that ammonium sulfate as the salting-out agent can form double salt MgSO4·(NH4)2SO4·6H2O with magnesium sulfate, realizing better separation of sodium sulfate and magnesium sulfate. On the basis of the Pitzer model of electrolyte solution theory, the ionic strength function was introduced to express the interaction parameters between two kinds of electrolyte at 0 °C. The interaction parameters were regressed from the experimental data of the ternary systems, and the solubilities of Na2SO4–MgSO4–(NH4)2SO4–H2O system at 0 °C were calculated. The results showed that the calculated values were well consistent with experimental results.

There is a great deal of H2O2 loss and low production benefit in the traditional technology of urea peroxide production. To develop a new method of producing urea peroxide, the mutual solubilities in the quaternary system Na2CO3–CO(NH2)2–H2O2–H2O were measured, and the corresponding diagrams were plotted at 0 °C and 25 °C. Based on the analysis about the phase diagram, this work put forward a new technology of the combination production of urea peroxide and sodium percarbonate. Urea peroxide was first produced at 0 °C; then sodium percarbonate was produced according to the reaction of Na2CO3 with the residual solution after urea peroxide production at 25 °C. After sodium percarbonate production, the residual solution was evaporated and concentrated and then used to produce urea peroxide, and thereby the stable recycle production of CO(NH2)2·H2O2 and Na2CO3·1.5H2O2 could be realized.

In order to develop a new process for concentrating and separating sodium sulfate (Na2SO4) and magnesium sulfate (MgSO4) of the bloedite based on tetrahydrofuran (THF) hydrate method, the equilibrium of the ternary systems THF–Na2SO4–H2O and THF–MgSO4–H2O and the quaternary system THF–Na2SO4–MgSO4–H2O were measured at 5 °C, and the phase digrams of these three systems were investigated. It showed that the mass percentage of Na2SO4 (MgSO4) in equilibrium liquid was higher than in feed and we could obtain Na2SO4·10H2O and MgSO4·7H2O in turn. It proved that THF hydrate could be used to the concentration and separation of Na2SO4 and MgSO4. The extended Pitzer model of the electrolyte–electrolyte–nonelectrolyte–water system was derived and applied into THF–Na2SO4–MgSO4–H2O system and its subsystems. The necessary thermodynamic parameters had been derived from a least-squares optimization program. The model calculation value was in good agreement with experimental solubility for ternary and quaternary mixtures, which indicated that the Pitzer model could be successfully used to predict the phase equilibrium of the electrolyte–electrolyte–nonelectrolyte–water systems containning THF hydrate.

In order to separate ZSM-5 zeolite powders from solution easily, a series of magnetic ZSM-5 zeolites were prepared by hydrothermal synthesis with the addition of magnetic Fe3O4 particles during the crystalline process. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared (IR) spectrum, energy dispersive X-ray (EDX), specific surface area, magnetic susceptibility and adsorption capability. It was found that the magnetic ZSM-5 zeolites had good magnetism and the magnetic susceptibility increased with the increasing amount of Fe3O4 particles. Compared with the pure ZSM-5 zeolite, the adsorption capability of magnetic ZSM-5 zeolites was acceptable. When the magnetic zeolites were used to adsorb Pb2+ from solution, the magnetic zeolite powder could be conveniently separated with magnetic separation technology.

Bloedite (Na2SO4·MgSO4·4H2O) is an important natural chemical resource. So far, it has not been developed and utilized effectively because of its separation difficulties. To develop a new technology to produce Na2SO4 and Mg–N compound fertilizers by a CO(NH2)2 salting-out method to separate bloedite, the mutual solubilities of the ternary system Na2SO4–CO(NH2)2–H2O and the quaternary system Na2SO4–MgSO4–CO(NH2)2–H2O at 25 °C were measured, and the phase digrams of these two systems were investigated. According to the phase diagram analysis, it indicates that, by using the CO(NH2)2 salting-out method, Na2SO4 and MgSO4 in bloedite can achieve better separation and anhydrous sodium sulfate can be directly obtained. The yield of Na2SO4 was 90.98 % in the case of the mother solution without cycling and utilizing. Adding a certain amount of CO(NH2)2 into the mother solution after Na2SO4 separation, MgSO4·CO(NH2)2·2H2O can be obtained. After separating MgSO4·CO(NH2)2·2H2O from the solution, the remain mother solution was recycled to dissolve bloedite. The new technology can get stable recycle production.

To develop a new method for separating the residual liquid of peroxide urea production by the formation of gas hydrate, the equilibrium of the system water + hydrogen peroxide + urea + carbon dioxide was studied under the conditions of P = (1.2 to 1.9) MPa and T = (273.15 to 303.15) K. The equilibrium pressure and temperature of gas hydrate formation were investigated at the different concentrations of hydrogen peroxide and urea with the anionic surfactant sodium dodecyl sulfate (SDS) and the sodium dodecyl benzene sulfonate (SDBS) in the system and without either. It was found that the equilibrium pressure of gas hydrate formation increased with the increase of temperature and the mass fraction of hydrogen peroxide and urea. The addition of anionic surfactant SDBS and SDS lowered the equilibrium pressure of the gas hydrate formed. The equilibrium pressure of the gas hydrate formed was calculated by Chen−Guo thermodynamic model, and the calculated values were in accord with the experimental results.