Phase Equilibria At 323.15 K And Metastable Zone Width Of Boric Acid In The Quinary System LiCl-NaCl-CaCl₂-H₃BO₃-H₂O

In view of the characteristics of boric acid brine resources in the Nanyishan area of Qaidam Basin,the isothermal dissolution equilibrium method was used to study the phase equilibrium and phase diagram of the five-component system LiCl-NaCl-CaCl₂-H₃BO₃-H₂O and its subsystems in this paper.The laser turbidity method was used to study the metastable zone width of boric acid in the five-component system and two ternary subsystems.The results are as follows.The phase diagram of ternary system LiCl-H₃BO₃-H₂O has an invariant point at323.15 K,two crystallization fields for LiCl·H₂O and H₃BO₃,and two unvariant solubility curves saturated with LiCl·H₂O and H₃BO₃,respectively.The phase diagram of ternary system CaCl₂-H₃BO₃-H₂O at 323.15 K has an invariant point,two univariant solubility curves,and two single salt crystalline regions corresponding to H₃BO₃ and CaCl₂·2H₂O,respectively.Each crystallization zone exists in the form of stable single salt.In the phase diagram of quaternary system LiCl-NaCl-H₃BO₃-H₂O,there are three solid phase crystallization regions（LiCl·H₂O,NaCl and H₃BO₃）,three univariant solubility curves and one invariant point.The compositions for the invariant point are w（NaCl）=0.35%,w（LiCl）=44.75%and w（H₃BO₃）=11.23%.The phase diagram of quaternary system NaCl-CaCl₂-H₃BO₃-H₂O has a invariant point.The equilibrium liquid phase compositions of invariant point are w（NaCl）=0.73%,w（CaCl₂）=54.40%,w（H₃BO₃）=3.76%.The phase diagram consists of three univariant solubility curves,three solid phase crystallization regions for NaCl,CaCl₂·2H₂O and H₃BO₃.The phase diagram of the quinary system LiCl-NaCl-CaCl₂-H₃BO₃-H₂O cosaturated with NaCl consists of one invariant point.The liquid phase compositions of point E are w（LiCl）=26.11%,w（CaCl₂）=28.46%,w（NaCl）=0.42%,w（H₃BO₃）=6.57%,w（H₂O）=38.44%.The corresponding equilibrium solid phases for the invariant point are NaCl,LiCl·H₂O,CaCl₂·2H₂O and H₃BO₃.There are three univariate solubility curves in the phase diagram.The three crystallization regions are CaCl₂·2H₂O,H₃BO₃,LiCl·H₂O.Both LiCl and CaCl₂ can reduce the solubility of boric acid to some extent.In the study of the metastable zone width of boric acid in the quinary system LiCl-NaCl-CaCl₂-H₃BO₃-H₂O and the ternary system LiCl-H₃BO₃-H₂O and CaCl₂-H₃BO₃-H₂O,it was found that the metastable zone width was wider at low temperature and narrower at the high temperature.With the increase of concentration of LiCl and CaCl₂,the solubility of boric acid in the system decreases,and the metastable zone width of boric acid becomes wide.The nucleation order for boric acid was obtained by changing the cooling rate.The nucleation order for boric acid increases with the increase of temperature...