Mechanochemical synthesis of Ca-Al-Fe layered double hydroxide for efficient phosphate removal from aqueous solution

A simple mechanochemical method was utilized to synthesize Ca-Al-Fe layered double hydroxide (CAF-LDH) and the Ca-Al-Fe-layered double oxide (CAF-LDO) was obtained by calcining CAF-LDH at 500 degrees C. From the results of XRD, FTIR, SEM and zeta potential, both CAF-LDH and CAF-LDO contained abundant functional groups, such as -OH, NO3- and CO32-. Over 90% removal efficiency for 25.0 mg/L phosphate was achieved with CAF-LDH and CAF-LDO at pH 3-10. The adsorption process quickly reached equilibrium within only 30 min. The isothermal and kinetics data better fit the Langmuir model (LM) and the pseudo- second-order (PSO) model, respectively. Based on the adsorption tests, zeta potential and FTIR, the interaction mechanisms were mainly electrostatic attraction and inner-sphere surface complexation (ISSC). In addition, CAF-LDH and CAF-LDO presented efficient regeneration, reusability, selectivity and potential application to remove phosphate in the water environment.