Adsorption of Phosphate in Aqueous Solution by Magnetite Modified with Diethylenetriamine

A magnetic adsorbent, amine-functionalized silica magnetite (NH2-Al/SiO2/Fe3O4), has been synthesized to behave as an cationic adsorbent by adjusting the pH value of the aqueous solution to make amino groups protonated. NH2-Al/SiO2/Fe3O4 was used to adsorb phosphate ions in an aqueous solution in a batch system, and the maximum adsorption were found to occur at pH 3.0. The adsorption equilibrium data were all fitted the Langmuir isotherm equation reasonably well, and the maximum adsorption capacities of phosphate ions were more than 40 mg g(-1) and increased with elevating temperature. The enthalpy (ΔH0) and entropy (ΔS0) values of NH2-Al/SiO2/Fe3O4 with the adsorption reaction of phosphate ions were 11.98 KJ mol(-1) and 0.095 KJ (T mol)(-1), respectively. A pseudo-second-order model also could best describe the adsorption kinetics, and the derived activation energy for phosphate ions was 20.2 kJ mol(-1). The optimum condition to desorb phosphate ions from NH2-Al/SiO2/Fe3O4 is provided by a solution with 0.05 M NaOH.