Phase equilibria of aqueous quaternary system Li+, K+, NH+4 // Cl- - H2O at 298.2 K

The equilibrium solid phase composition of the ternary system Li+, NH+4 // Cl- - H2O and the quaternary system Li+, K+, NH+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+, NH+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+, NH+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+, NH+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+, NH+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. © 2022 Chemical Industry Press. All rights reserved.