Solid–Liquid Equilibria in the Quinary system Na⁺, K⁺//Cl^–, Br^–, SO₄^2––H₂O at 373 K

Abstract

H 2 O at 373 K were measured by the isothermal solution saturation method, and the equilibrium solid phases, solubilities and densities of saturated solutions were determined experimentally. Using the experimental results, the dry salt phase diagrams, water diagrams, and the densities versus composition diagrams were plotted (saturated with Na 2 SO 4 and K 2 SO 4 , respectively). The experimental results show that there is solid solution formed in the quinary system Na + , K + //Cl − , Br − , SO 4 2− −H 2 O at 373 K. The two projected phase diagrams of this system all consist of one univariant curve, two crystallization fields, and have no invariant point. Saturated with the salt Na 2 SO 4 , the crystallization forms are the double salt Na 2 SO 4 •3K 2 SO 4 (Gla) and the solid solution Na(Cl,Br); the two crystallization forms are Na 2 SO 4 •3K 2 SO 4 (Gla) and the solid solution K(Cl,Br) saturated with the salt K 2 SO 4 .

Solid–Liquid Equilibria in the Quinary System Na+, K+//Cl–, Br–, SO42––H2O at 323.15 and 348.15 K

“…From a practical view, we hope to simplify it into a plane diagram, so a salt has to be abandoned. Normally, the salt with the lowest solubility and easiest to crystallize in the system is chosen as the abandoned salt . In the quinary system Na + , K + //Cl – , Br – , SO 4 2– –H 2 O, the solubility of sulfates is often lower than that of other salts.…”

“…The comparison of the phase diagrams of the quinary system Na + , K + //Cl – , Br – , SO 4 2– –H 2 O (saturated with Na 2 SO 4 ) at 323.15, 348.15 and 373.15 K is displayed in Figure . The patterns of the phase diagrams at 323.15 and 348.15 K are similar, and both have an invariant point, three univariant curves, and three crystallization zones corresponding to Na 2 SO 4 ·3K 2 SO 4 , Na­(Cl, Br), and KBr.…”

“…The comparison of the solubility data of the quinary system Na + , K + //Cl – , Br – , SO 4 2– –H 2 O (saturated with K 2 SO 4 ) at 323.15, 348.15, and 373.15 K is exhibited in Figure . It is clear that all phase diagrams at three temperatures contain only one univariant curve and two crystallization zones, i.e., Na 2 SO 4 ·3K 2 SO 4 and K­(Cl, Br).…”

“…In bittern, Mg 2+ is easy to separate in the form of Mg­(OH) 2 , and the remaining quinary system Na + , K + //Cl – , Br – , SO 4 2– –H 2 O is an important complicated subsystem. By now, the solid–liquid equilibrium in the quinary system Na + , K + //Cl – , Br – , SO 4 2– –H 2 O at 373.15 K has been reported previously, yet it is not enough for the comprehensive utilization of bittern, which requires the solubility data at different temperatures. When the temperature is below 323.15 K, the quaternary subsystems have multiple invariant points and generate three solid solutions Na­(Cl, Br)·2H 2 O, Na­(Cl, Br) and K­(Cl, Br), which makes the phase diagram of the quinary system more complicated and unfavorable for the extraction of bromide.…”

Study of Phase Equilibrium of NaBr + KBr + H2O and NaBr + MgBr2 + H2O at 313.15 K

“…To extract relevant products from the potassium, magnesium, and bromine salt mine, it is essential to investigate the phase equilibrium of NaBr + KBr + H 2 O and NaBr + MgBr 2 + H 2 O. By now, a number of studies on the Br-bearing phase equilibria have been done, such as quaternary systems KCl−KBr−K 2 SO 4 −H 2 O at 323 K, 348 K, and 373 K [5][6][7], NaBr−SrBr 2 −MgBr 2 −H 2 O and KBr−SrBr 2 −MgBr 2 −H 2 O at 323 K [8], and quinary system Na + , K + //Cl − , Br − , and SO 4 2− −H 2 O at 373 K [9]. The two ternary systems NaBr−KBr−H 2 O and NaBr−MgBr 2 −H 2 O also have been reported at 323 K and 348 K [10][11][12].…”