Application of magnetite modified with polyacrylamide to adsorb phosphate in aqueous solution

Phosphate is one of the main contaminants responsible for the eutrophication of surface waters, and adsorption is a potential treatment method of this pollutant. A magnetic adsorbent manufactured from magnetite (Fe3O4) can be easily recovered from treated water by magnetic force, without requiring further downstream treatment. In this research, the surface of magnetite modified with oleic acid and polyacrylamide (PAM/oleic acid/Fe3O4) was used to adsorb phosphate in an aqueous solution in a batch system. The phosphate adsorption behavior by PAM/oleic acid/Fe3O4 was in good agreement both with the Langmuir and Freundlich adsorption isotherm, and the maximum adsorption capacity (qm) and Gibbs free energy of phosphate at 298 K was 28.95 mg/g and −12.89 kJ/mol, respectively. A pseudo-second-order model could best describe the adsorption kinetics, and the derived activation energy was 28.29 kJ/mol. The optimum condition to desorb phosphate from PAM/oleic acid/Fe3O4 is provided by a solution with 0.5 M NaOH.

► A magnetic adsorbent modified with polyacrylamide is a new material to adsorb phosphate anions.
► The amine groups of the magnetic adsorbents can be used to adsorb and desorb phosphate ions by adjusting the solution pH values.
► The synthetic adsorbent is easy to recover by applying external magnetic force.