Isopiestic measurements and thermodynamic model for the ternary system {Li2B4O5(OH)4) + LiB5O6(OH)4 + H2O} and its subsystem at 288.15 K and ambient pressure

Abstract The isopiestic equilibria for the systems {Li2B4O5(OH)4 + H2O}, {LiB5O6(OH)4 + H2O} and {Li2B4O5(OH)4 + LiB5O6(OH)4 + H2O} at 288.15 K and ambient pressure were measured by the isopiestic method using a modified gravimetric isopiestic apparatus. The water activities and osmotic coefficients were determined based on the sodium chloride standard reference solution. On the basis of Pitzer model, an extended Pitzer model was developed to describe the thermodynamic properties of the aqueous systems containing different forms of lithium borates, then the Pitzer single salt parameters β(0), β(1), β(2) and Cϕ for the binary systems {Li2B4O5(OH)4 + H2O} and {(LiB5O6(OH)4 + H2O} and mixing ion-interaction parameters θ B 4 O 5 OH 4 , B 5 O 6 OH 4 and ψ Li , B 4 O 5 OH 4 , B 5 O 6 OH 4 for the ternary system {Li2B4O5(OH)4 + LiB5O6(OH)4 + H2O} were fitted with the experimental osmotic coefficients using the Fortran 97 program. Meanwhile, the water activities were calculated by the Pitzer parameters, and the good agreement between the calculated water activities and experimental results of this ternary system indicated that the Pitzer parameters obtained in this work were reliable.