Fe 3O 4 and γ-Fe 2O 3 nanoparticles for the adsorption of Co 2+ from aqueous solution

Abstract

The adsorption of Co 2+ ions from nitrate solutions using iron oxide nanoparticles of magnetite (Fe 3O 4) and maghemite ( γ-Fe 2O 3) has been studied. The adsorption of Co 2+ ions on the surface of the particles was investigated under different conditions of oxide content, contact time, solution pH, and initial Co 2+ ion concentration. It has been found that the equilibrium can be attained in less than 5 min. The maximum loading capacity of Fe 3O 4 and γ-Fe 2O 3 nanoparticles is 5.8 × 10 −5 and 3.7 × 10 −5 mol m −2 , respectively, which are much higher than the previously studied, iron oxides and conventional ion exchange resins. Co 2+ ions were also recovered by dilute nitric acid from the loaded γ-Fe 2O 3 and Fe 3O 4 with an efficiency of 86 and 30%, respectively. That has been explained by the different mechanisms by including both the surface and structural loadings of Co 2+ ions. The surface adsorption of Co 2+ on Fe 3O 4 and γ-Fe 2O 3 nanoparticles has been found to have the same mechanism of ion exchange reaction between Co 2+ in the solution and proton bonded on the particle surface. The conditional equilibrium constants of surface adsorption of Co 2+ on Fe 3O 4 and γ-Fe 2O 3 nanoparticles have been determined to be log K = − 3.3 ± 0.3 and − 3.1 ± 0.2 , respectively. The structural loading of Co 2+ ions into Fe 3O 4 lattice has been found to be the ion exchange reaction between Co 2+ and Fe 2+ while that into γ-Fe 2O 3 lattice to fill its vacancy. The effect of temperature on the adsorption of Co 2+ was also investigated, and the value of enthalpy change was determined to be 19 kJ mol −1.