Solid-liquid phase equilibria of the quinary system containing sodium, potassium, lithium, chloride and pentaborate ions at 298.15 K and 101.325 kPa

Abstract

The solid–liquid phase equilibria of the quinary system (Li+, Na+, K+//Cl−, B5O8− - H2O) saturated with NaCl at 298.15 K and 101.325 kPa were investigated with the isothermal dissolution method. On the basis of experimental data, the dry-salt phase diagram, water-phase diagram and sodium-phase diagram in the quinary system were established for the first time. In this quinary dry-salt phase diagram, there are three invariant points corresponding to F1 (NaCl + KCl + LiCl·H2O + LiB5O8·5H2O), F2 (NaCl + KCl + LiB5O8·5H2O + KB5O8·4H2O) and F3 (NaCl + LiB5O8·5H2O + NaB5O8·5H2O + KB5O8·4H2O), seven isothermal dissolution curves, and five crystallization regions saturated with NaCl corresponding to LiCl·H2O, KCl, LiB5O8·5H2O, NaB5O8·5H2O, KB5O8·4H2O. The areas of crystallized regions decrease according to the order of NaB5O8·5H2O, KB5O8·4H2O, LiB5O8·5H2O, KCl, and LiCl·H2O, which all are saturated with sodium chloride. It was found that neither double salt nor solid solution was formed. In addition, the diagram of physicochemical properties including densities and refractive indices against J(B5O8−) was also established, and it shows that density and refractive index of the solution in the quinary system change regularly with the increasing of Jänecke index J(B5O8−) in the solution. These results on the phase diagram of the quinary system can supply a theoretical guide to separate and purify the valuable alkali pentaborates.