Bimetal oxide magnetic nanomaterials (MnFe2O4 and CoFe2O4) were synthesized and characterized with transmission electron microscope (TEM), X-ray powder diffraction (XRD), vibrating sample magnetometer (VSM), and X-ray photoelectron spectroscopy (XPS). The adsorption of arsenic on these nanomaterials was studied as a function of pH, initial arsenic concentration, contact time and coexisting anions. The Langmuir and Freundlich isotherm models were applied to fit the adsorption data, and the maximum adsorption capacities of arsenite (AsIII) and arsenate (AsV) on MnFe2O4 were 94 and 90 mg g−1, and on CoFe2O4 were 100 and 74 mg g−1, respectively. MnFe2O4 and CoFe2O4 showed higher AsIII and AsV adsorption capacities than the referenced Fe3O4 (50 and 44 mg g−1, respectively) prepared by the same procedure. Quantificational calculation from XPS narrow scan results of O(1s) spectra of adsorbents indicated that the higher adsorption capacities of AsIII and AsV on MnFe2O4 and CoFe2O4 than on Fe3O4 might be caused by the increase of the surface hydroxyl (M–OH) species. Phosphate and silicate were powerful competitors with arsenic for adsorptive sites on the adsorbent. Desorption study showed that over 80% of AsIII and 90% of AsV could be desorbed from MnFe2O4 with 0.1 M NaOH solution.

Arsenite and arsenate adsorption on coprecipitated bimetal oxide magnetic nanomaterials: MnFe2O4 and CoFe2O4