关键词: 相平衡, 溶解性, 热力学性质, 固溶体, 水合物

Abstract:

The equilibrium solid phase composition of the ternary system Li⁺, \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+} // Cl^- - H₂O and the quaternary system Li⁺, K⁺, \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+} // Cl^- - H₂O were determined by isothermal dissolution method at 298.2 K. The composition of the equilibrium solid phase at the invariant point of the ternary system Li⁺, \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+} // Cl^- - H₂O was determined by wet residue method and X-ray diffraction method. It was found that a solid solution (NH₄Cl) _x (LiCl·H₂O)_1-x was formed. The composition of the equilibrium solid phase at the invariant point of the quaternary system Li⁺, K⁺, \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+} // Cl^--H₂O was determined by X-ray diffraction and SEM. It was found that solid solutions (NH₄Cl) _x (LiCl·H₂O)_1-x, (NH₄Cl) _x (KCl)_1-x and (KCl) _x (NH₄Cl)_1-x were formed. The stable phase diagram of the ternary system Li⁺, \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+} // Cl^--H₂O consists of two invariant points, three uninvariant curves and three crystallization regions, the area of crystallization region decreases in the order of NH₄Cl > (NH₄Cl) _x (LiCl·H₂O)_1-x > LiCl·H₂O. The stable phase diagram of the quaternary system Li⁺, K⁺, \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+} // Cl^--H₂O consists of three invariant points, eight uninvariant curves and six crystallization regions, the area of the crystallization regions decreases in the order of (KCl) _x (NH₄Cl)_1-x > NH₄Cl > KCl > (NH₄Cl) _x (KCl)_1-x >(NH₄Cl) _x (LiCl·H₂O)_1-x > LiCl·H₂O. The results show that in the chloride system at 298.2 K, both lithium ammonium and potassium ammonium can form solid solution, and potassium ammonium is easier to form solid solution than lithium ammonium and precipitate in large quantities, which increases the difficulty of separation of lithium potassium ammonium chloride.

Key words: phase equilibria, solubility, thermodynamics properties, solid solution, hydrate