Study on the Metastable Equilibria of the Salt Lake Brine System Li2SO4 + Na2SO4 + K2SO4 + Li2B4O7 + Na2B4O7 + K2B4O7 + H2O at 288 K

An experimental study on phase equilibria at 288 K in the quinary system Li + + Na + + K + + SO 4 2- + B 4 O 7 2- + H 2 O was performed using the isothermal evaporation method. Equilibrium solubility and density of the solution were measured. The equilibrium phase diagram for the solution saturated with the salt Li 2 B 2 O 4 ·16H 2 O was constructed. The phase diagram of this system consists of 7 invariant points, 14 univariant curves, and 8 crystallization fields corresponding to potassium tetraborate pentahydrate (K 2 B 4 O 7 ·5H 2 O), borax (Na 2 B 4 O 7 ·10H 2 O), potassium sulfate, lithium sulfate monohydrate (Li 2 SO 4 ·H 2 O), sodium sulfate, lithium−potassium sulfate double salt (Li 2 SO 4 ·K 2 SO 4 ), lithium−sodium sulfate double salt (Li 2 SO 4 ·Na 2 SO 4 ), and potassium−sodium sulfate double salt (3K 2 SO 4 ·Na 2 SO 4 ). There are three kinds of double salts formed in the system. The crystallization forms of lithium and potassium borate were K 2 B 4 O 7 ·5H 2 O and Li 2 B 2 O 4 ·16H 2 O, respectively, which are different from the usual forms of K 2 B 4 O 7 ·4H 2 O and Li 2 B 4 O 7 ·3H 2 O that occur at stable equilibrium.