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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 30min 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 74.83mg/g at 10, 30 and 50°C, respectively. For As(V), the adsorption capacities at these temperatures were 88.44, 95.37, and 105.25mg/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⁻, SO₄^2-, and NO₃^- had no effect on the adsorption capacity. However, the presence of PO₄^3-, which has a similar outer electronic structure to that of the arsenic species, led to a …