Optimization of dechlorination conditions and reaction kinetics of aluminum gel

A new aluminum gel dechlorinating agent was used to replace sodium meta-aluminate in the traditional Friedel's salt precipitation method, and the effects of chemical dosage, reaction time, reaction temperature, initial Cl- concentration, and coexisting SO42- concentration on the dechlorination effect were investigated, and the mechanism of the influence of temperature on the reaction behavior was revealed through the kinetic study of the reaction at different temperatures. The results showed that when n(Ca2+)∶n(Al3+) was 3 and n(Al3+)∶n(Cl-) was 1, the reaction time was 60 min, the reaction temperature was 20-40 ℃, and the initial Cl- concentration was 200 mmol/L, the Cl- removal rate and Al utilization rate were both maintained at about 60%. In addition to the main product Friedel's salt(Ca4Al2(OH)12Cl2), the by-products tricalcium aluminate(Ca3Al2(OH)12) and Ca(OH)2 were detected in the reaction precipitates. Appropriate elevation of the temperature not only improves the reaction rate, but also enhances the efficiency of the dechlorination reaction. However, excessively high temperature increases the tendency for side reactions to occur, leading to a phase transition of Ca4Al2(OH)12Cl2 to produce Ca3Al2(OH)12, which results in a significant decrease in the Cl- removal rate.