Removal of Chromium From Aqueous Solution: A Study on the Effects of PH and Temperature Using Iron Oxide Nanomaterials

Removal of Chromium(III) or (VI) from aqueous solution was achieved by using nanophases Fe₃O₄, MnFe₂O₄, and Fe₂O₃core shell was achieved  through a precipitation method.  The Fe₃O₄, Fe₂O₃ core shell, and MnFe₂O₄ were characterized using x-ray diffraction and had crystal structures that corresponded to the literature, in addition these materials are magnetic.    Batch pH experiments were performed to determine the optimum pH for binding using 300 ppb of either Cr(III) or (VI), 10 mg of the nanomaterials Fe₃O₄, MnFe₂O₄, or Fe₂O₃ core shell and one hour of contact time.  The optimal pH for the binding of Cr(III) and (VI) were pH 6 and pH 3, respectively for all three nanomaterials.  Batch isotherm studies were performed using the same three nanomaterials to determine the binding capacity of Cr(III) and (VI) to the iron oxide nanomaterials.  The binding capacities (ug/g) were 10,638 (Fe₃O₄), 7189 (MnFe₂O₄), and 10,845 (Fe₂O₃ core shell) for Cr(III) and 3455 (Fe₃O₄), 3211(MnFe₂O₄), and 3267 (Fe₂O₃ core shell) for Cr(VI) which were determined using the Langmuir isotherm model.  Furthermore a thermodynamic study was also conducted to determine the Gibbs free energy  of binding.  The DG values were -9.30, -2.53, -9.12 for Cr (III) and -1.45 -1.33 -0.38 for Cr (VI) for Fe₃O₄, MnFe₂O₄, and Fe₂O₃ core shell respectively. Further studies were performed to determine the enthalpy of binding of Cr(III) and Cr(VI) to the nanomaterials.