Phase Equilibrium Study of the AlCl3–CaCl2–H2O System for the Production of Aluminum Chloride Hexahydrate from Ca-Rich Flue Ash

Abstract

The study of the solid–liquid phase equilibrium for the AlCl3–CaCl2–H2O system is of significance to separate aluminum chloride hexahydrate from the leachate obtained by the reaction of Ca-rich fly ash and a waste hydrochloride from chemical plant. The phase equilibrium data for the binary AlCl3–H2O system and the ternary AlCl3–CaCl2–H2O system over the temperature range from 278.15 K to 363.15 K were measured. A rigorous and thermodynamically consistent model representing the AlCl3–CaCl2–H2O system developed on the basis of the Pitzer’s activity coefficient model embedded in the Aspen Plus. On the basis of this, the phase behavior of the ternary AlCl3–CaCl2–H2O system at different temperatures was visualized with lucidity on an equilateral triangle. The phase-equilibrium diagram generated by modeling was illustrated to identify the course of crystallization to recover AlCl3·6H2O from the solutions containing calcium chloride. All of these will provide a thermodynamic basis for the separation of aluminum ...