Solubility Measurement and Calculation of the Quaternary System Kcl–Kbr–Nacl–Nabr–H2o and its Ternary Subsystem at 333.15 K

Solid solution hinders the extraction of bromine resources from bittern. It makes a lot of sense to study the solid−liquid equilibrium in the water salt system containing Cl & Br. The solubilities of the quaternary system KCl–KBr–NaCl–NaBr–H2O and its ternary subsystem NaBr–KBr–H2O at 333.15 K were determined by the isothermal dissolution method, and the corresponding phase diagrams were conducted. The phase diagram of the ternary subsystem belongs to simple type and consists of one invariant point, two univariant curves, and two crystallization fields corresponding to NaBr and KBr, respectively. The phase diagram of the quaternary system is composed of one univariant curve and two crystallization regions of solid solution, i.e., Na(Cl, Br) and K(Cl, Br). The solubilities of the ternary subsystem NaBr–KBr–H2O were calculated based on the Pitzer model, and the results are in accordance with the measured data. An improved model was employed to predict the phase equilibrium data of the ternary systems NaBr–NaCl–H2O, KBr–KCl–H2O and the quaternary system KCl–KBr–NaCl–NaBr–H2O at 333.15 K. The calculated results coincide with the experimental values, implying that the prediction method is feasible.