Measurements and theoretical simulations of phase equilibria in the quaternary systems NaBr + KBr + SrBr2 + H2O, NaBr + MgBr2 + SrBr2 + H2O and their subsystems at 273.15 K

Abstract

Since various mineral elements (such as sodium, potassium, strontium, bromine) are rich in underground brine in Sichuan Basin of China, to utilize the bromine resources rationally, the phase equilibria of the quaternary systems NaBr + KBr + SrBr2 + H2O, NaBr + MgBr2 + SrBr2 + H2O and their subsystems at 273.15 K were studied with the means of isothermal dissolution equilibrium method. The research systems are three ternary systems (NaBr + SrBr2 + H2O, KBr + SrBr2 + H2O and MgBr2 + SrBr2 + H2O) and two quaternary systems (NaBr + KBr + SrBr2 + H2O and NaBr + MgBr2 + SrBr2 + H2O). The corresponding solubility phase diagrams of the research systems listed above were plotted based on the measured experimental data.The experimental results indicate that there is no formation of solid solution or double salts in five systems. Five phase diagrams all belong to hydrate type I and contain one invariant point. In three ternary systems, there are two isothermal solubility curves and two crystallization fields, and the equilibrium solid phases are NaBr•2H2O and SrBr2•6H2O in the ternary system NaBr + SrBr2 + H2O, KBr and SrBr2•6H2O in the ternary system KBr + SrBr2 + H2O, and MgBr2•6H2O and SrBr2•6H2O in the ternary system MgBr2 + SrBr2 + H2O, respectively. There are three isothermal solubility curves and three crystallization fields in two quaternary systems. The equilibrium solid phases are NaBr•2H2O, KBr, and SrBr2•6H2O in the quaternary system NaBr + KBr + SrBr2 + H2O. In the quaternary system NaBr + MgBr2 + SrBr2 + H2O, the salts NaBr•2H2O, MgBr2•6H2O and SrBr2•6H2O coexist at the invariant point.The unreported mixing ion-interaction parameters of Pitzer equations θMg, Sr, ΨMg, Sr, Br, ΨNa, Sr, Br, and ΨK, Sr, Br are fitted with the solubility data at 273.15 K. The Pitzer ionic interaction model and the required parameters were employed to predict the solubilities of salts in five systems. The calculated results show that the predicted values are in accordance with the measured data, which verify the reliability of the selected parameters.