LAUSR

Abstract Using an isothermal dissolution equilibrium method, solid-liquid equilibria in the quaternary system NaBr–KBr–Na 2 SO 4 –K 2 SO 4 –H 2 O were studied at T  = 348 K. The phase diagram, water diagram and the density-composition diagram were plotted according to the experiment results. One double salt Na 2 SO 4 ·3K 2 SO 4 was found in the quaternary system at T  = 348 K. There are five areas of crystallization, seven univariant solubility curves, and three invariant points. Respectively, the five crystallization regions are Na 2 SO 4 ·3K 2 SO 4 , NaBr, KBr, Na 2 SO 4 and K 2 SO 4 . Based on the chemical model of Pitzer's electrolyte solution theory, the solubilities of the quaternary systems NaCl–KCl–Na 2 SO 4 –K 2 SO 4 –H 2 O, NaBr–KBr–Na 2 SO 4 –K 2 SO 4 –H 2 O have been calculated at T  = 348 K. The calculation diagrams were plotted. Comparing experimental measurement with calculation, the results showed that the calculated results are in accordance with experiments.