Phase diagrams of the Li2SO4-LiCl-H2O system at 450 and 470°C

Abstract

Phase equilibria were studied at 450 and 470°C in the Li2SO4-LiCl-H2O ternary system with boundary binary subsystems of various types: type 1 subsystem LiCl-H2O and type 2 subsystem Li2SO4-H2O with critical points \(p\left( {G = L - S_{Li_2 SO_4 } } \right)\) and \(Q\left( {L_1 = L_2 - S_{Li_2 SO_4 } } \right)\). It was shown that, in the system, there are two regions of three-phase equilibria (G-L-S) and (L1-L2-S), which are separated by a fluid region \(\left( {F - S_{Li_2 SO_4 } } \right)\), and also there are monovariant critical curves of two types \(\left( {G = L - S_{Li_2 SO_4 } } \right)\) and \(\left( {L_1 = L_2 - S_{Li_2 SO_4 } } \right)\). With increasing temperature, both three-phase regions and critical curves respectively approach each other. The fact that the p-T parameters of different critical curves near 50–51 MPa and 470°C coincide, whereas the compositions of the critical solutions are essentially different, indicates that there may emerge a four-phase equilibrium \(\left( {G - L_1 - L_2 - S_{Li_2 SO_4 } } \right)\) and there is no double homogeneous critical point \(\left( {G = L - S_{Li_2 SO_4 } \Leftrightarrow L_1 = L_2 - S_{Li_2 SO_4 } } \right)\) in this ternary system.