LAUSR

Abstract In order to guide the separation of valuable lithium and potassium pentaborate productions, the phase equilibria for the two reciprocal quaternary systems (Na+, K+//Cl−, B5O8− - H2O) and (Li+, K+//Cl−, B5O8− - H2O) at 298.15 K and atmospheric pressure were studied using the isothermal dissolution method. Based on experimental data, the phase diagrams as well as the diagrams between physicochemical properties including densities and refractive indices against J(K+) in the two systems were established for the first time. For the former system, there are four crystallization zones corresponding to halite (NaCl, Ha), sylvite (KCl, Sy), sodium pentaborate pentahydrate (NaB5O8·5H2O, Sp5) and potassium pentaborate tetrahydrate (KB5O8·4H2O, Pp4), two invariant points of three solid phases existed (Ha + Sy + Pp4) and (Ha + Sp5 + Pp4), and five univariant curves, but for the later system, there are also four crystallization zones corresponding to Sy, Pp4, lithium chloride monohydrate (LiCl·H2O, Lc1) and lithium pentaborate pentahydrate (LiB5O8·5H2O, Lp5), two invariant points of three solid phases existed (Sy + Lc1 + Pp4) and (Lc1 + Pp4 + Lp5), and five univariant curves, respectively. The diagrams for the physicochemical properties including density and refractive index against J(K+) in the solution of two systems were also established.