Enhanced Adsorption of Mercury(II) and Cadmium(II) from Aqueous Solution onto Rice Bran Modified with Chelating Ligands

To enhance the removal of mercury (Hg(II)) and cadmium (Cd(II)) from aqueous solutions, rice bran (RB) was reacted with epichlorohydrin and then modified with ethylenediamine and sodium chloroacetate to bear iminodiacetate functional groups. The modified rice bran (MRB) was characterized by Fourier transform-infrared spectroscopy (FT-IR), thermogravimetric analysis (TG), energy dispersive spectroscopy (EDS), back titration, and X-ray photoelectron spectroscopy (XPS). The adsorption properties of MRB for Hg(II)/Cd(II) ions were also evaluated in batch experiments. The sorption kinetic experimental data were best described by the pseudo-second-order model. The maximum adsorption capacity (163.9 mg/g for Hg(II) at pH 5.0 and 106.4 mg/g for Cd(II) at pH 6.0) was observed at 298 K, and the isotherm adsorption equilibrium of MRB was followed by Langmuir isotherm equation. The major adsorption mechanisms should be predominantly controlled by the formation of complexes between the functional groups of MRB and Hg(II)/Cd(II) ions as well as ion-exchange. The regeneration experiments showed that the MRB could be successfully reused for six cycles when 0.1 M HCl eluent was used.