Solubility and Density Measurements of Concentrated Li₂B₄O₇ + Na₂B₄O₇ + K₂B₄O₇ + Li₂SO₄ + Na₂SO₄ + K₂SO₄ + H₂O Solution at 273.15 K

Abstract

The isothermal evaporation method was employed to investigate the phase equilibria in the quinary system Li2B4O7 + Na2B4O7 + K2B4O7 + Li2SO4 + Na2SO4 + K2SO4 + H2O at 273.15 K. The solubilities and densities of the equilibrated solution were measured. The crystalloid forms of the solid phase were determined using chemical analysis and an X-ray diffraction method. On the basis of the experimental data, the stereophase diagram, the projected phase diagram saturated with Li2B4O7, the projected phase diagram saturated with Na2B4O7, and the lithium content diagram of the quinary system were plotted. The stereophase diagram consists of six invariant points, eighteen univariant curves, and eight crystallization fields corresponding to sodium sulfate decahydrate (Na2SO4·10H2O), potassium sulfate, lithium sulfate monohydrate, sodium tetraborate decahydrate (borax, Na2B4O7·10H2O), potassium tetraborate tetrahydrate (K2B4O7·4H2O), lithium metaborate octahydrate (LiBO2·8H2O), a potassium and lithium sulfate double salt (KLiSO4), and a sodium and lithium sulfate double salt (3Na2SO4·Li2SO4·12H2O). The double salt glaserite (3K2SO4·Na2SO4) is not found at this temperature. The salt borax has the largest crystallization field and can be easily separated from the solution. The lithium content changes irregularly along with the evaporation process, thus the lithium salts are separated in a dispersed way.