Determination and Calculation of the Solubility of the Quaternary System NaBr-KBr-NH4Br-H2O Containing Solid Solutions at 298.15 and 323.15 K

In order to fully recover and utilize the bromine and potassium resources in seawater bitter brine after magnesium extraction, the solubilities of the quaternary system NaBr-KBr-NH4Br-H2O and its subsystem KBr-NH4Br-H2O at 298.15 and 323.15 K were investigated by the isothermal dissolution equilibrium method. The equilibrium solid phase composition was determined by the wet residue method and X-ray diffraction. Phase diagrams were drawn by using experimental data. At 298.15 K, K-NH4 solid solution is formed in the quaternary system NaBr-KBr-NH4Br-H2O, and the dry-base phase diagram consists of one invariant point and three crystalline regions (NaBr<middle dot>2H(2)O, (K,NH4)Br, (NH4,K)Br). At 323.15 K, the dry basis phase diagram of this quaternary system consists of one invariant point and three crystalline regions (NaBr, (K,NH4)Br, (NH4,K)Br). According to a comparison with the quaternary phase diagram at 298.15 K, the crystalline zone of NaBr<middle dot>2H(2)O vanishes, and a single salt crystalline region of NaBr emerges following the temperature increase. Meanwhile, the crystallization zone of (K,NH4)Br increases and that of (NH4,K)Br decreases. At 298.15 K, the phase diagram of its ternary subsystem consists of one invariant point and two crystalline regions ((K,NH4)Br, (NH4,K)Br). No single salt crystalline region is shown in the phase diagram. By deriving the extended Pitzer model and applying it to the systems NaBr-KBr-NH4Br-H2O and KBr-NH4Br-H2O, the solubilities of the quaternary and ternary systems with solid solutions at 298.15 K were calculated without taking into account the ionic interaction parameter. The results were in general agreement with the experimental values.