Selective radionuclide and heavy metal sorption using functionalised magnetic nanoparticles for environmental remediation

Abstract

In this paper the removal of a wide range of heavy metal ions from different chemical environments has been explored with the use of phosphate-functionalised superparamagnetic iron oxide nanoparticles (SPIONs), specifically magnetite (Fe₃O₄). These novel complexes have shown a high level of selectivity and increased loading capacity with the ions selected for the study: Na(I), K(I), Cs(I), Ca(II), Cu(II), Co(II), Ni(II), Cd(II), Mg(II), Sr(II), Pb(II), Al(III), Mn(II), Eu(III) and Fe(III). The loading capacities established using these NP-complexes have been shown to be higher than that of conventional surface-ligand systems. The development of these phosphate functionalised complexes, (PO)_x-Fe₃O₄ and (PO)_x-SiO₂@Fe₃O₄, has successfully shown the feasibility of removing the selected metal ions at pH 1, pH 3 and pH 7. The maximum adsorption capacities of the complexes were tested with single-metal adsorption experiments, showing a degree of selectivity towards all metal ions studied. Multi-metal adsorption experiments were conducted to determine the selectivity of the NP-complexes in the presence of a range of competing ions. These experiments simulated real-world environments that contain the selected heavy metals, which cause great concern for humans and the environment. These experiments allowed for the successful determination of a selectivity series, highlighting the steps in which the various metal ions are removed after sequential sorption experiments. The results that have been presented in this paper highlight the potential use of these magnetic phosphate NP-complexes for selective heavy metal removal from contaminated aqueous wastewaters in the industrial world.