A New Method Of Solid-liquid Equilibrium Phase Diagram Prediction Of Salt-water System

Based on double-AT method and the analysis of topological properties of phase-diagrams, a new method was proposed to predict the solubilities of salt-water system. Using the method solubilities and diagrams of these systems at 298K were predicted:1. Binary systems Na+/S042-H2CK Na+/CO32-H2O;2. Ternary system Na+,K+/CC>32-H2O, whose crystallization fields in different literatures are different from each other, and the existence of the solid phase Na2CC>3H2O was explained;3. Quartemary systems Na+,K+/Cr,HCO3-H2O and Na+,K+/SO42,HCO3-H2O, quinary system Na+,KVcr, HCO3,SO42--H2O, whose relative prediction and experimental study have not been found.4. Quinary system Na+,K+/Cr,SO42-,CO32--H2O, both the solubility data of this system and the solubility product of the solid phase 9Na2SO4'2Na2CCb'KCl have not been found.In order to simulate the conditions in nature and salt chemical industry production, two methods were developed to predict the solubilities when a system is unsaturated with solid phase i: 1) the solid-liquid equilibrium system is diluted to some extent, which is saturated with phase i, and those equilibrium solid phases are added enough into the solution except phase i, when this system reach equilibrium again, the solubilities can be computed; 2) When concentration of an ion is controlled to keep phase i unsaturated, the solubilities can also be computed. By the former method, the author predicted the solubilities of the quinary system Na+,K+/Cr,SO42,CO32-H2O at 298K which is unsaturated with NaCl, and compared them with those of same system saturated with NaCl. By the latter method, the solubilities of these systems at 298K were predicted: ternary and quartemary subsystems Li-Na-K-H-Cl-H2O at different H+ concentration, system Li+, X(Na+, K+,Mg2+)/CT-H2O, Li+,Na+,K+ /Cl-H2O, Li+,K+,Mg+ /C1--H2O,Lf ,Na+,K+/Cr,CO32-H2O at different Li+ concentration.This work provides exact and detailed data for salt chemical industry production and study of the forming conditions of natural salt minerals. It is of practical significance hi separating salts through salting-out, especially extracting lithium from brine.