Solid and liquid metastable phase equilibria in the aqueous quaternary system Li⁺, Mg²⁺//SO₄ ^2–, borate-H₂O at 273.15 K

Abstract

The metastable phase equilibria of the Li⁺, Mg²⁺//SO₄ ^2–, borate-H₂O system at 273.15 K were studied using isothermal evaporation method. The dry-salt phase diagram, water-phase diagram and the physicochemical property diagrams of the system were plotted with the metastable solubility values and physicochemical properties corresponding to density, refractive index, pH value and conductivity. The dry-salt diagram was composed of four crystallizing zones[lithium sulfate hydrate(Li₂SO₄·H₂O), epsomite(MgSO₄·7H₂O), lithium metaborate octahydrate(LiBO₂·8H₂O), and hungchaoite(MgB₄O₇·9H₂O)], five univariant curves and two invariant points (Li₂SO₄·H₂O+MgSO₄·7H₂O+MgB₄O₇·9H₂O and Li₂SO₄·H₂O+LiBO₂·8H₂O+MgB₄O₇·9H₂O). Li₂B₄O₇ converted into LiBO₂ in solution. Comparing the metastable phase diagram at 273.15 K and stable phase diagram at 298.15 K for the system, the crystallized area of Li₂SO₄·H₂O and MgSO₄·7H₂O became large, whereas, the other phase regions became small. The J(H₂O) changes regularly with increasing J(SO₄ ^2‒), and the physicochemical properties change regularly with the concentration of B₄O₇ ^2‒ increasing.

Keywords

Metastable phase equilibrium / Phase diagram / Solubility / Lithium metaborate octahydrate / Hungchaoite

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