Solid-liquid phase equilibria and theoretical simulation of the quaternary system NaBr + KBr + MgBr2 + H2O and its subsystem NaBr + MgBr2 + H2O at 308.2 K and 1–500 bar

Abstract

Solid-liquid phase equilibria of bromine salt can be indicative of Br evolution in Br-rich underground brines of Sichuan Basin in China. Consequently, the solid–liquid phase equilibria of the ternary subsystem NaBr + MgBr2 + H2O and quaternary system NaBr + KBr + MgBr2 + H2O at 308.2 K are determined by the isothermal dissolution equilibrium method. Then, Pitzer ion interaction model and particle swarm optimal algorithm are used to predict the phase equilibria of the systems listed above. The calculated solubilities are in good agreement with the experimental data.Considering the pressure conditions in deep strata, furthermore, we develop a thermodynamic prediction model of the phase equilibria for the systems changing with pressure. The thermodynamic volume properties of solution at 308.2 K with increasing pressure (1–500 bar) are evaluated. The unreported parameters of pressure dependency (Av,V¯MX(aq)0,βMX(0),v,βMX(1),v,CMXv) in Pitzer model at 308.2 K in the studied systems of this work are fitted accordingly. As a result, the effects of pressure on the phase equilibria are investigated in detail, and phase diagrams of the systems at 1–500 bar are also drawn and discussed. This work can provide important thermodynamic data for the salt mineral exploitation of the actual deep strata brines.