Study on the adsorption mechanism of chloride ion in aqueous solution on Mg/Al-CLDH modified by high temperature calcination

Abstract

The co-deposition method prepared the Mg/Al double hydroxyl composite metal hydroxide with interlayer anion CO32−. Mg/Al-CLDH was obtained by calcination at high temperatures, and its potential to adsorb chloride ions in an aqueous solution was studied. The adsorption effect was the best when the roasting temperature was 550 ℃. The optimal adsorption temperature in the sodium chloride solution of 300 mg/L was 65 ℃ and reached equilibrium after a 180 min reaction. The unit adsorption mass can get 172 mg/L in the sodium chloride solution with a 2000 mg/L concentration. According to the adsorption equilibrium isotherm and adsorption equilibrium kinetic analysis, the maximum unit adsorption capacity of Mg/Al-CLDH can reach 182.88 mg/g, and the adsorption mode is mainly monolayer adsorption and chemical adsorption. The adsorption of chloride ions primarily depends on the interlayer ion exchange and filling. High-temperature calcination makes part of CO32− in the original structure separate from the interlayer in the form of CO2. Part of the chloride ions in the solution enter the interlayer to fill the vacancy. On the other hand, chloride ions can be fixed by ion exchange with the remaining CO32−.