Fast Removal and Recovery of Cr(VI) Using Surface-Modified Jacobsite (MnFe₂O₄) Nanoparticles

In this work, the effectiveness of surface-modified jacobsite (MnFe₂O₄) nanoparticles was investigated for the removal and recovery of Cr(VI) from synthetic wastewater. Ten nanometer modified MnFe₂O₄ nanoparticles were produced to be a new adsorbent using a co-precipitation method followed by a surface redox reaction. The equilibrium time for Cr(VI) adsorption onto modified MnFe₂O₄ nanoparticles was as short as 5 min, and the adsorption data fit the Langmuir model well. The maximum uptake of 31.5 mg of Cr(VI)/g of modified MnFe₂O₄ was obtained at pH 2, which was comparable with other common adsorbents such as activated carbon and sawdust. The effects of ligands (EDTA, SO₄^2-, NH₄⁺) and ionic strength were studied in a pH range of 2−10. EDTA and SO₄^2- inhibited the adsorption of Cr(VI) over the entire pH range studied, whereas NH₄⁺ enhanced the uptake of Cr(VI) at pH greater than 6.5. The mechanisms leading to Cr(VI) adsorption by modified MnFe₂O₄ nanoparticles were determined by X-ray diffraction and X-ray photoelectron spectroscopy to be a combination of electrostatic interaction and ion exchange. Regeneration studies indicated the potential reuse of the modified MnFe₂O₄ nanoparticles without sacrificing adsorption capacity and the possible recycling of Cr(VI) without changing the valence.