Removal of arsenic contaminants with magnetic γ-Fe2O3 nanoparticles

Magnetic γ-Fe2O3 nanoparticles synthesized by a co-precipitation method at room temperature have been used to remove As(III) and As(V) from their aqueous solutions. The adsorption of As(III) or As(V) was found to be saturated within 30 min and has been interpreted in terms of a Langmuir model at different temperatures. The adsorption capacities for As(III) reached 59.25, 67.02, and 74.83 mg/g at 10, 30 and 50 °C, respectively. For As(V), the adsorption capacities at these temperatures were 88.44, 95.37, and 105.25 mg/g, respectively. The effects of pH and competing ions on the adsorption of arsenite and arsenate have also been examined. The adsorption capacity remained unchanged in the range of pH 3 to 11. The presence of Cl−, SO42-, and NO3- had no effect on the adsorption capacity. However, the presence of PO43-, which has a similar outer electronic structure to that of the arsenic species, led to a significant reduction in the adsorption capacity. It is concluded from FTIR and XPS analyses that chemical binding with OH on the adsorbent surface is responsible for the adsorption of As(III) and As(V). The saturated magnetic γ-Fe2O3 nanoparticles could be recovered by applying a magnetic field of strength greater than 0.35 T. Arsenic compounds were eluted from the magnetic adsorbent following treatment with 1 m NaOH, leading to regeneration of the magnetic γ-Fe2O3 nanoparticles. The nanoparticles retained over 40% of their initial adsorption capacity for arsenic compounds after 6 cycles.