Solid-liquid equilibria in the quaternary system Na+, K+//Br−, B4O72−-H2O at 298 K

According to the compositions of the underground gasfield brines in the west of Sichuan Basin, the solubilities and densities of the solid-liquid equilibria in the quaternary system Na+, K+//Br−, B4O72−-H2O at 298 K were determined by the method of isothermal solution saturation. From the experimental data, the phase diagram, water content diagram and density-composition diagram were obtained. This quaternary system is of simple eutectic type, without double salt and solid solution. There are two invariant points, five univariant curves, four fields of crystallization in the system. The equilibrium solid phases are Na2B4O7·10H2O, K2B4O7·4H2O, NaBr·2H2O and KBr. Na2B4O7·10H2O has a larger crystallization field, and NaBr·2H2O has a smaller crystallization field. It is also found that bromide has the salting-out effect on borate in the quaternary system Na+, K+//Br−, B4O72−-H2O at 298 K.