Quaternary Invariant Point Research Articles

Solid–Liquid Phase Equilibria of the Aqueous Quaternary System Rb+, Cs+, Mg2+//SO42− - H2O at T = 323.2 K

Sulfate-type salt lakes constitute over half of the total salt lakes in China and are rich in rare elements, such as rubidium and cesium. However, the complex interactions between ions make the separation and extraction process quite challenging. To address this, phase equilibrium studies were conducted on the sulfate system containing rubidium, cesium, and magnesium. Specifically, the phase equilibria of the aqueous quaternary system Rb+, Cs+, Mg2+//SO42− - H2O at 323.2 K were investigated using the isothermal dissolution method. The solubility, density, and refractive index of the system were experimentally measured. The results indicate that the system at 323.2 K belongs to a complex type with the formation of one solid solution (Rb, Cs)2SO4 and two double salts (Rb2SO4·MgSO4·6H2O, Cs2SO4·MgSO4·6H2O). The corresponding phase diagram consists of four quaternary invariant points, nine univariate curves, and six crystallization regions. Among these, the crystalline region for Cs2SO4·MgSO4·6H2O is the largest, while that for the single salt Cs2SO4 is the smallest. Moreover, the crystalline regions for the double salt and solid solutions are significantly larger than those for the single salt, highlighting the difficulty in separation of valuable single salts. A comparison of multi-temperature phase diagrams from 298.2 K to 323.2 K reveals that the crystalline form of MgSO4 changes from MgSO4·7H2O (298.2 K) to MgSO4·6H2O (323.2 K). As the temperature increases, the phase regions for Rb2SO4, Cs2SO4, (Rb, Cs)2SO4, and Cs2SO4·MgSO4·6H2O expand, while the phase region of Rb2SO4·MgSO4·6H2O contracts, indicating that the single salts (Rb2SO4, Cs2SO4) are more readily precipitated at higher temperature, which provides theoretical guidance for the future production and separation of Rb, Cs, and Mg from sulfate-type salt lakes.

Solid-liquid phase equilibria in the aqueous system containing the chlorides of potassium, ammonium, and calcium at 298.2, 323.2, and 348.2 K

In order to obtain the crystalline forms of the salts of the potassium, ammonium, calcium coexisting chloride system, the phase equilibria relationship of quaternary system K+, NH4+, Ca2+//Cl–-H2O at 298.2, 323.2, and 348.2 K was studied by isothermal dissolution equilibrium method. The solubility and density of equilibrium liquid phases of the system were experimentally determined; X-ray powder diffractometer was used to determine the compositions of the equilibrium solid phase at the quaternary invariant point. It is found that the quaternary system is a complex system at these three temperatures. The phase diagram at 298.2 K consists of three invariant points, seven univariate curves and five crystalline phase regions, forming the solid solutions (NH4Cl)x(KCl)1–x and (KCl)x(NH4Cl)1–x; while at 323.2 and 348.2 K the phase diagram consists of five invariant points, eleven univariate curves and seven crystalline phase regions, the double salts (KCl·CaCl2) and (2NH4Cl·CaCl2·3H2O), solid solutions (KCl)x(NH4Cl)1–x and (NH4Cl)x(KCl)1–x were formed. Among them, the crystalline phase region of solid solution (KCl)x(NH4Cl)1–x is the largest at three temperatures, indicating that it is the easiest to crystallize in this system. Comparing the phase diagrams of the quaternary system at 298.2, 323.2, and 348.2 K, it can be seen that the crystalline form of CaCl2 changes with the increase of temperature: CaCl2·6H2O at 298.2 K, CaCl2·2H2O at 323.2 and 348.2 K. From 323 to 348 K, the crystalline phase regions of (KCl·CaCl2) and (2NH4Cl·CaCl2·3H2O) increased gradually.

Solid-Liquid Phase Equilibria of a Quaternary Sulfate-Type System Containing Lithium, Rubidium, and Magnesium at 298.2 K.

The aim of this study was to obtain the relationship between ion interactions and the crystallization patterns of salt species in the lithium-rubidium-magnesium sulfate system at 298.2 K. The phase equilibria of the aqueous quaternary system Li+, Rb+, Mg2+//SO42--H2O were studied by the isothermal dissolution method at T = 298.2 K and p = 94.77 kPa. The density, refractive index, and composition of equilibrium solution were determined, on the basis of which solid-liquid phase diagrams and density/refractive index vs composition diagrams were drawn. The phase diagram consists of four quaternary invariant points and six crystallization regions, corresponding to the crystallization areas of single salts Rb2SO4, Li2SO4·H2O, and MgSO4·7H2O, as well as double salts 3Li2SO4·Rb2SO4·2H2O, Li2SO4·Rb2SO4, and Rb2SO4·MgSO4·6H2O. Notably, rubidium-containing double salts occupy more than 50% of the entire phase diagram area. The results indicate that the interactions between Li+ and Rb+ with coexisting Mg2+ and SO42- are complex, leading to the formation and precipitation of various lithium- and rubidium-bearing double salts, which hinder the effective concentrations of lithium and rubidium during the solar evaporation process in salt pans. Additionally, a multitemperature comparison of the solid-liquid phase diagrams at 273.2, 298.2, and 308.2 K reveals that temperature is also a significant factor influencing the solid-phase types and crystallization areas. For instance, the crystallization form of the double salt 3Li2SO4·Rb2SO4·2H2O changes to 3Li2SO4·Rb2SO4 at 308.2 K and the crystallization area of Li2SO4·Rb2SO4 gradually decreases, while the crystallization area of Rb2SO4·MgSO4·6H2O generally exhibits an increasing trend.

Solid-liquid phase equilibrium for the system ammonium polyphosphate-urea ammonium nitrate-potassium chloride-water at 273.2 K

Based on the dynamic method, a quaternary system of ammonium polyphosphate (APP)-urea ammonium nitrate (UAN, CO(NH2)2-NH4NO3)-potassium chloride (KCl)-H2O and its subsystems (APP-[CO(NH2)2-NH4NO3]-H2O, KCl-[CO(NH2)2-NH4NO3]-H2O and APP-KCl-H2O) were systematically investigated at the temperature of 273.2 K. Each ternary phase diagram contains one invariant point and three crystallization regions. The crystallization regions are: (1) (NH4)3HP2O7, (NH4)4P2O7 and ((NH4)3HP2O7 + (NH4)4P2O7) for APP-[CO(NH2)2-NH4NO3]-H2O diagram; (2) KCl, KNO3 and (KCl + KNO3) for KCl-[CO(NH2)2-NH4NO3]-H2O diagram and (3) (NH4)3HP2O7, KCl and ((NH4)3HP2O7 + KCl) for APP-KCl-H2O diagram. The quaternary phase diagram of APP-[CO(NH2)2-NH4NO3]-KCl-H2O has no quaternary invariant point but includes four solid phase crystallization regions, i.e., (NH4)3HP2O7, (NH4)4P2O7, KNO3 and KCl, in which the KNO3 region occupies the largest area. The maximum total nutrient content (N + P2O5 + K2O) existing as ionic forms in the APP-[CO(NH2)2-NH4NO3]-H2O, KCl-[CO(NH2)2-NH4NO3]-H2O, APP-KCl-H2O and quaternary systems is 44.70%, 32.86%, 45.56% and 46.23% (mass), respectively, indicating that the maximum nutrient content can be reached using raw materials of the corresponding systems to prepare liquid fertilizer. In the quaternary system, the content of NH4+-N ascends with the increase of the total nutrient content, while the contents of NO3--N and CO(NH2)2-N increase with elevated total N. This work can help optimize the operating parameters for the production, storage and transportation of liquid fertilizers.

Stable Phase Equilibria of the Quaternary Water-Salt System Li+, Rb+, Mg2+//SO4 2--H2O at T = 273.2 K.

The phase equilibria for the quaternary system Li+, Rb+, Mg2+//SO4 2- - H2O at 273.2 K were studied by the isothermal dissolution equilibrium method. Based on the measured data, the space diagram, stable phase diagram, water content diagram, and the diagram of density vs composition are plotted. The stable phase diagram in the system consists of four quaternary invariant points, nine univariate curves, and six crystallization zones. For the invariant points, E1 and E4 belong to the commensurate type, and E2 and E3 belong to the incommensurate type. The order of the crystallization area is Rb2SO4·MgSO4·6H2O > 3Li2SO4·Rb2SO4·2H2O > Li2SO4·Rb2SO4 > MgSO4·7H2O > Li2SO4·H2O > Rb2SO4. The density of the equilibrium liquid changed regularly with the content of Rb2SO4 in the solution. By comparing the stable phase diagram of the partial ternary subsystems at T = 273.2 K and T = 298.2 K, it is found that the crystallization regions of Rb2SO4 increases with the decrease in temperature, which indicates that cooling is conducive to the crystallization of Rb2SO4. By comparing the stable phase diagram of the system at T = 273.2 K and T = 308.2 K, it was found that the system was composed of four invariant points, nine univariate curves, and six crystal regions. The double salt 3Li2SO4·Rb2SO4·2H2O is converted to 3Li2SO4·Rb2SO4. The crystallization region of single salt MgSO4·7H2O, Rb2SO4 and double salt Li2SO4·Rb2SO4 decreased obviously.

Phase Equilibria of the Aqueous Quaternary System Li+, Rb+, Cs+//SO42–-H2O at T = 273.2 K

The phase equilibria of the quaternary system Li+, Rb+, Cs+//SO42–-H2O at T = 273.2 K was investigated by the isothermal dissolution method. The solubility and density of the system were measured and the related phase diagram, water content diagram, and density vs composition diagram were plotted. The solid phase of the quaternary invariant point was identified by the X-ray diffraction method and the solid solution morphology was analyzed by scanning electron microscopy. Results show that the stable phase diagram consists of 6 invariant points, 13 uninvariant curves, and 8 crystallization regions (corresponding to single salts Li2SO4·H2O, Rb2SO4, and Cs2SO4; double salts 3Li2SO4·Rb2SO4·2H2O, 3Li2SO4·Cs2SO4·2H2O, Li2SO4·Rb2SO4, and Li2SO4·Cs2SO4; and solid solution [(Rb, Cs)2SO4]). Also, the crystallization region of double salt 3Li2SO4·Rb2SO4·2H2O is the largest, which means that it is easiest to precipitate from this system. Meanwhile, rubidium and cesium easily form a solid solution in the sulfate system, which increases the difficulty of separating the two elements. Comparing the stable phase diagram of the ternary subsystems at T = 273.2 K and T = 298.2 K, it is found that the crystallization regions of Rb2SO4, Cs2SO4, [(Rb, Cs)2SO4], and 3Li2SO4·Cs2SO4·2H2O increase with the decrease of temperature, indicating that cooling is conducive to the crystallization of Rb2SO4, Cs2SO4, [(Rb, Cs)2SO4], and 3Li2SO4·Cs2SO4·2H2O.

Phase Equilibria on the Reciprocal Quaternary System K+, Rb+ // Cl–, and Borate–H2O at T = 323.2 K and p = 94.77 kPa

The isothermal dissolution method was applied for the phase equilibrium experiment of the quaternary system K+, Rb+ // Cl–, and borate–H2O at T = 323.2 K and p = 94.77 kPa. The solubilities and refractive indices (nD) of the system were determined experimentally. The coexisting salts of the quaternary invariant points were identified using the X-ray diffraction (XRD) method. Based on the measured data, the stable phase diagram and the figures of water content and refractive index (nD) vs composition were plotted for this system at 323.2 K. The results show that the system belongs to a complex type with the formation of a solid solution [(K, Rb)Cl]. The stable phase diagram consists of three quaternary invariant points, seven isothermal dissolution curves, and five crystallization regions corresponding to KCl, RbCl, RbB5O6(OH)4·2H2O, K2B4O5(OH)4·2H2O, and [(K, Rb)Cl]. The size of the RbB5O6(OH)4·2H2O crystallization zone is the largest among the coexisting salts in the quaternary system, which means it is the most easily crystallized from the mixed solution containing potassium, rubidium, chloride, and borate.

Phase Equilibria for the Reciprocal Aqueous Quaternary System Li+, Rb+//Cl−, Borate–H2O at 323.2 K

The isothermal dissolution equilibrium method was applied for the solid–liquid equilibria experiments of the reciprocal aqueous quaternary system Li+, Rb+//Cl−, borate–H2O at 323.2 K, and the relevant diagrams (phase diagram, water content diagram, density/refractive index against composition diagram) were plotted. It was found that there are two commensurate type quaternary invariant points with three-salt cosaturated, five univariant curves, and four crystallization fields corresponding to four single salts, rubidium chloride (RbCl), lithium chloride monohydrate (LiCl·H2O), lithium tetraborate trihydrate (Li2B4O7·3H2O), and rubidium pentaborate tetrahydrate (RbB5O8·4H2O), respectively. LiCl·H2O has a salting out effect on other coexisting salts and the size of the LiCl·H2O crystallization field is the smallest. Li2B4O7·3H2O has the largest crystallization field, which demonstrates that Li2B4O7·3H2O can be more easily separated from the solutions.

Solid-liquid phase equilibria of quaternary systems Na+//Cl−, CO32−, SO42− - H2O and Na+//Cl−, CO32−, NO3− - H2O at T = 313.15 K

The solid-liquid equilibrium of quaternary systems (Na+//Cl−, CO32−, NO3− -H2O) and (Na+//Cl−, CO32−, SO42− -H2O) at 313.15 K was studied by an isothermal solution saturation method and the solubility of salts and equilibrium solid phases in the two systems was determined. The solid phases formed in the systems studied were determined by the Schreinemaker wet residue method. Based on the measured data, dry-salt phase diagrams and the relevant water-phase diagrams were plotted in the two systems. The stable phase diagram of Na+//Cl−, CO32−, NO3− -H2O at 313.15 K is characterized by one quaternary invariant point (Q), three univariant curves, and three crystallographic forms (corresponding to NaCl, NaNO3 and Na2CO3·H2O). The crystallization region of NaNO3 (I) is the smallest, and its solubility is the greatest, which indicates that NaNO3 has a strong salt-out effect on Na2CO3·H2O and NaCl. The composition of the solution at equilibrium corresponding to invariant point is w(NaCl) = 9.76 wt%, w(NaNO3) = 32.79 wt%, w(Na2CO3) = 6.10 wt%. Therefore, it can be considered that there is no double salt and solid solution in the quaternary system, which belongs to the simple quaternary system. For the quaternary systems (Na+//Cl−, CO32−, SO42− -H2O) at 313.15 K, experimental results indicate that there are four crystallographic forms (NaCl, Na2CO3·H2O, Na2SO4 and Bur (2Na2SO4 Na2CO3)), five univariant curves, and two invariant points corresponding to three salts, that is (NaCl + Na2SO4 + 2Na2SO4 Na2CO3) and (NaCl + Na2CO3·H2O + 2Na2SO4 Na2CO3), respectively. The experimental results show that this system is a complex eutectic type, and no solid solutions are found at the investigated temperature. All the physical properties (ρ, η, nD) of the equilibrium two quaternary systems change regularly with concentration change of the liquid phase. The phase equilibria in the quinary Na+//C1−, SO42−, CO32−, NO3−-H2O system at 313.15 K were also studied using the through and intermediate translation techniques together. All data and results obtained in this paper are of great significance to the design and optimization of the fractional crystallization process of the high-saline wastewater in coal chemical industry.

Solid–Liquid Phase Equilibrium in Aqueous Quaternary System Li+,Rb+,Mg2+//Borate–H2O at T = 323 K

The stable phase equilibria, densities, and refractive indices of the aqueous quaternary system Li+,Rb+,Mg2+//borate–H2O at 323 K were determined by the isothermal dissolution method. It was found that the phase diagram consists of one quaternary invariant point, two isothermal dissolution curves, and three fields of crystallization corresponding to three single salts Li2B4O7 · 3H2O, MgB4O7 · 9H2O, and RbB5O8 · 4H2O, respectively. The size of crystallization regions of salt decreased in the order MgB4O7 · 9H2O > RbB5O8 · 4H2O > Li2B4O7 · 3H2O. The comparison of phase diagrams of the system at 298–348 K shown that the crystalline form of salts lithium borate, magnesium borate, and rubidium borate did not change at 298–348 K. The crystalline area of MgB4O7 · 9H2O is the largest than that of 298 and 348 K. The crystalline area of RbB5O8 · 4H2O is the smallest than that of 298 and 348 K, while the crystalline are of Li2B4O7 · 3H2O is larger than that of 298 K, and smaller than that of 348 K.

Prediction of phase equilibria in multicomponent water-salt systems by means of translation method

The translation method which can produce all the geometrical figures and closed phase equilibria diagram for multicomponent water-salt systems was described. The phase equilibria in quinaryNaCl - KCl -MgCl2 - CaCl2 - H2O (25°C) system which is an important part of the more complex oceanic Na, K, Mg, Ca//Cl, SO4- H2O system were determined using translation method. Three invariant points of quadruple saturation, tenmonovariant curves of triple saturation and twelvedivariant fields of double saturation salts were identified in the system. Two of the curves extend between the quinary invariant points while the other eightare generated from extension of the relevant quaternary invariant points into the quinary composition. A total phase equilibria diagram for the quinary NaCl - KCl - MgCl2 - CaCl2 - H2O system at 25°C was constructed on the basis of obtained results. The diagram was fragmented into divariant fields of common crystallization of two salts. A good agreement was observed between the results obtained in this work and the available data in literature.

Partition of the Quaternary Reciprocal System Na,Rb||F,I,CrO4 and Investigation of the Stable Tetrahedron NaF–RbI–RbF–Rb2CrO4

The quaternary reciprocal system Na,Rb||F,I,CrO4 was studied, low-melting mixtures based on which are promising as fusible electrolytes for chemical current sources, heat-storage materials, and media for growing single crystals. The system was partitioned into simplexes using graph theory, and the tree of phases of the system was constructed. The tree of phases is linear and contains four stable tetrahedra sharing stable cutting triangles. The combined stable tetrahedron NaF–RbI–RbF–Rb2CrO4 was investigated by differential thermal analysis. The crystallization surface of this stable tetrahedron is represented by the volumes of sodium fluoride, rubidium iodide, rubidium fluoride, rubidium chromate, and the compound Rb3CrO4F. Monovariant equilibrium lines meet at two quaternary invariant points: eutectic E◻491 and peritectic P◻508.

Solid-liquid phase equilibria of quaternary system NH4+//C1−, SO42−, H2PO4−–H2O and its subsystems NH4+//C1−, SO42−–H2O, NH4+//C1−, H2PO4−–H2O at 313.15 K

Solid–liquid phase equilibrium and physical properties of ternary systems NH4Cl-NH4H2PO4-H2O, NH4Cl-(NH4)2SO4-H2O and quaternary system NH4Cl-(NH4)2SO4-NH4H2PO4-H2O at 313.15K and atmospheric pressure were obtained by means of an isothermal solution method. The solid phases formed in the systems studied were determined by the Schreinemaker wet residue method. Based on the measured data, corresponding phase diagrams and the diagrams of physical properties versus composition were plotted. Neither complex salt nor solid solution is found in these systems at 313.15K. The ternary phase diagram of NH4+//C1−, H2PO4−–H2O contains one invariant point, and three crystallization regions (NH4H2PO4, NH4Cl, and (NH4Cl+NH4H2PO4)). The ternary phase diagram of NH4+//C1−, SO42−–H2O is similar to the previous one, also contains one invariant point, three crystallization regions ((NH4)2SO4, NH4Cl, and (NH4Cl+(NH4)2SO4)). The quaternary phase diagram of NH4+//C1−, SO42−, H2PO4−–H2O contains one quaternary invariant point, three crystallization regions ((NH4)2SO4, NH4Cl, and NH4H2PO4), and crystallization field of NH4H2PO4 is the largest one of them. All results obtained in this work can be used for the stripping process of solvent extraction in the production of potassium dihydrogen phosphate.

Solid–Liquid Equilibria in the Quaternary System K+//H2PO42–, SO42–,Cl––H2O at 298.2 K and 323.2 K

The solubility data of the quaternary system K+//H2PO42–, SO42–, Cl––H2O is basically required for the design and optimization of the crystallization process of KH2PO4 which is produced by the solvent extraction method using the wet-process H3PO4 and KCl as the raw materials. In this study, the solubility data of the quaternary system K+//H2PO42–, SO42–, Cl––H2O at 298.2 K and 323.2 K were investigated by the isothermal solution saturation method. The solubilities of salts and equilibrium solid phases were determined. The phase and water content diagrams were constructed based on the experimental results. The appearance of the phase diagram at 323.2 K is similar to that at 298.2 K, while the crystallization area of each salt varies slightly with the changing of temperature. The phase diagrams both contain one quaternary invariant point, three univariant curves, and three crystallization regions corresponding to KH2PO4, K2SO4, and KCl. The crystallization region of K2SO4 is the largest, while that of KCl i...

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.

Four-component reciprocal system Na,K∥F, CO3, WO4

The four-component reciprocal system Na,K∥F, CO3, WO4 has been studied using differential thermal analysis in combination with projective and differential geometry. The a priori prediction of the crystallization path (CP) shows six quaternary invariant points; of them, three are eutectics and the others are peritectics. The dominant exchange and complexing reactions have been recognized. The following four-component systems have been studied: (NaF)2-(KF)2-K2CO3-K3FWO4 (1), (NaF)2-K2CO3-K2WO4-K3FWO4 (2), (NaF)2-Na2CO3-Na2WO4-K2WO4 (3),, and (NaF)2-Na2CO3-K2CO3-K2WO4 (4); the coordinates of all quaternary invariant points have been determined.

Aqueous Phase Equilibria in the System CaO‐Al2O3‐CaCl2‐H2O: The Significance and Stability of Friedel's Salt

Friedel's Salt is a poorly understood phase in the CaO‐Al2O3‐CaCl2‐H2O system, which is critical in the function and stability of salt‐saturated portland cement‐based grouts. Such grouts are required to seal exploratory excavations in a radioactive waste repository sited in bedded salt. The phase equilibria of this system were investigated, and four quaternary invariant points were determined to allow construction of a phase diagram. The diagram is constructed using a plotting technique applicable to double‐decomposition systems or systems with a reciprocal salt pair. Statistical analysis of solution data was performed to assess the precision and accuracy of the invariant points.

Lignes monovariantes de l'isotherme 25°C du système quaternaire réciproque H 2SO 4H 3PO 4K 2SO 4K 3PO 4H 2O

Boundary curves and quaternary invariant points at 25°C of the reciprocal system H 2SO 4H 3PO 4K 2SO 4K 3PO 4H 2O The boundary curves and quaternary invariant points of the reciprocal system H 3PO 4K 2SO 4H 2SO 4K 3PO 4H 2O were investigated at 25°C and 1 bar by chemical analysis of solutions in equilibria with two or three salts, respectively. Thirteen compounds occur in this system. Only ten of them have crystallization areas inside Janecke's prism. These are K 2SO 4, K 2SO 4 · KHSO 4, K 2SO 4 · 7KHSO 4 · H 2O, KHSO 4, KHSO 4 · H 2SO 4, KH 2PO 4 · KHSO 4, KH 5(PO 4) 2, KH 2PO 4, H 3PO 4 and a solid solution K 8(H 2PO 4) 1+ x (HSO 4) 7- x (0 ⩽ x ⩽1) of substitution type, which is continuous between the two limiting compositions KH 2PO 4 · 7KHSO 4 and KH 2PO 4 · 3KHSO 4. The crystallization fields of KH 2PO 4 · 2K 2HPO 4 · H 2O, K 2HPO 4 · 3H 2O and K 3PO 4 · 7H 2O are very close to the solubility curves of the ternary system K 3PO 4H 3PO 4H 2O. The results are discussed and compared with bibliographic data.

Lignes monovariantes de l'isotherme 75 °C du système quaternaire réciproque: H3PO4–K2SO4–H2SO4–K3PO4–H2O

The boundary curves and quaternary invariant points of the reciprocal system H3PO4–K2SO4–H2SO4–K3PO4–H2O were investigated at 75 °C and 1 atm by chemical analysis of solutions in equilibria, respectively, with two or three salts. Eleven compounds occur in this system. Only eight of them have crystallization areas inside Janecke's prism; these are K2SO4, K2SO4•KHSO4, K2SO4•7KHSO4•H2O, KHSO4, KH2PO4•KHSO4, KH5(PO4)2, KH2PO4, and a solid solution K8(H2PO4)1+x(HSO4)7−x, 0 ≤ x ≤ 1, of substitution type continuous between the two limiting compositions KH2PO4•7KHSO4 and KH2PO4•3KHSO4. The crystallization fields of 3K2HPO4•KH2PO4•2H2O, K2HPO4, and K3PO4•3H2O are very close to the solubility curves of the ternary system K3PO4–H3PO4–H2O. Results are explained and discussed.

Hydration of Germanium Oxide Carnotite

The quaternary invariant point was reached in the CaO–GeO2–P2O5–H2O system by the hydration of germanium oxide carnotite. Complete reaction was achieved although the kinetics were very slow. Three products were identified by X‐ray diffraction: calcium germanate hydrate, hydroxyapatite, and calcium hydroxide. Energy dispersive X‐ray analyses established the compositions of the three phases present in the heterogeneous microstructure. Calcium germanate hydrate exhibited a fibrous habit and was present as large individual fibers as well as small thin fibers. The small fibers were intermixed with hydroxyapatite. The latter was observed to form feltlike assemblages. Stacked calcium hydroxide plates were unequivocally observed.