Al2O3 encapsulated by calcium alginate as composite for efficient removal of phosphate from aqueous solutions: batch and column studies

Activated alumina (Al2O3) has been widely used to remove aqueous anionic pollutants such as phosphate for preventing the eutrophication phenomenon. While Al2O3, as a fine powder material, cannot be stably packed into continuous flow treatment, which limits its practical applications. Herein, we proposed a new strategy in which Al2O3 was encapsulated by calcium alginate (CA) to fabricate Al2O3/CA composite, which has relatively large particle size and can be suitable for application in columns. The BET surface area of Al2O3/CA increased to 51.73 m2/g compared with 37.31 m2/g of Al2O3. The maximum adsorption capacity of phosphate on Al2O3/CA was estimated at 1.92-fold compared with that of pure Al2O3 by Langmuir fitting. The main mechanism of phosphate adsorption was the formation of aluminum phosphate precipitation. Moreover, the column studies showed that the adsorption of phosphate on Al2O3/CA was affected by the amount of outer calcium alginate, bed height, influent flow rates and phosphate concentration. This study demonstrated that Al2O3/CA composite has better adsorption capacity and can be used in the dynamic adsorption system as a promising approach for phosphate removal from water.