Removal of Chloride Ions from an Aqueous Solution Containing a High Chloride Concentration through the Chemical Precipitation of Friedel's Salt

This study explored the feasibility of removing chloride ions from an aqueous solution containing a high chloride concentration through the chemical precipitation of insoluble Friedel's salt, which was triggered by the addition of calcium and aluminum compounds. Calcium hydroxide (Ca(OH)(2)) and sodium aluminate (NaAlO2) were used as the reagents. Key factors for the removal of chloride ions, including the dosage of the reagents, reaction temperature, reaction time, initial pH, and initial chlorine concentration, were investigated. The results indicated that an optimal chloride removal efficiency of 84.0% was obtained when the molar ratio of Ca:Al:Cl was 10:4:1. The main crystal phases in the formed precipitates, confirmed through X-ray diffraction analysis, were Friedel's salt (Ca2Al(OH)(6)Cl center dot 2H(2)O), portlandite (Ca(OH)(2)), and katoite (Ca-3(Al(OH)(6))(2)). In addition, the chloride removal efficiency increased when the reaction temperature, initial pH, and initial chlorine concentration were higher. Chlorine removal could be further improved by conducting a second-stage treatment, regardless of the residual concentrations of chloride, calcium, and aluminum ions after the first-stage treatment.