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

摘要：

采用等温溶解平衡法研究了298.2 K三元体系Li⁺，\mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+} // Cl^--H₂O和四元体系Li⁺，K⁺，\mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+} // Cl^--H₂O的相平衡。采用湿渣法和XRD测定了三元体系共饱点处平衡固相组成，发现固溶体(NH₄Cl) _x (LiCl·H₂O)_1-x 形成；采用XRD和SEM测定了四元体系共饱点处平衡固相组成，发现固溶体(NH₄Cl) _x (LiCl·H₂O)_1-x 、(NH₄Cl) _x (KCl)_1-x 和 （KCl) _x (NH₄Cl)_1-x 形成。研究发现：298.2 K下，三元体系相图由2个共饱点、3条单变量曲线和3个结晶相区组成，结晶区面积按照NH₄Cl > (NH₄Cl) _x (LiCl·H₂O)_1-x > LiCl·H₂O顺序依次减小；四元体系相图包含3个共饱点、8条单变量曲线和6个结晶相区，结晶区面积按 (KCl) _x (NH₄Cl)_1-x > NH₄Cl > KCl > (NH₄Cl) _x (KCl)_1-x > (NH₄Cl) _x （LiCl·H₂O)_1-x > LiCl·H₂O顺序依次减小。结果表明：298.2 K时，在氯化物体系中，锂铵和钾铵均可形成固溶体，且钾铵比锂铵更容易形成固溶体而大量析出，增加了锂钾铵氯化物的分离难度。

关键词: 相平衡, 溶解性, 热力学性质, 固溶体, 水合物