Removal of U(VI) from aqueous solutions by the nano-iron oxyhydroxides

摘要

The nano-iron oxyhydroxides (α- and γ-FeOOH) were synthesized by oxidation of the various raw materials (FeSO _4 and FeCl _2) as iron precursors under alkaline conditions. Morphologies of nano-iron oxyhydroxides were characterized by high resolution transmission electron microscope (HRTEM), X-ray powder diffraction (XRD) and specific surface area (SSA), respectively. The removal of U(VI) from aqueous solution by nano-iron oxyhydroxides was also investigated as a function of contact time, U(VI) concentration, pH, ionic strength and temperature under ambient conditions. The occurrence of needle-like shape of nano-goethite and rod-like shape of nano-lepidocrocite were attributed to oxidization of Fe ~(2+) under different conditions in terms of XRD analysis and HRTEM images. The sorption results indicated that the removal of U(VI) strongly depended on pH and were independent of ionic strength. Langmuir model was employed to model the sorption isotherms of U(VI) at three various temperatures of 293, 313 and 333 K. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) computed from the temperature showed that sorption process of U(VI) on nanoiron oxyhydroxides was endothermic and spontaneous. The mechanism of U(VI) sorption on nano-iron oxyhydroxides was assumed to outer-sphere surface complexation at low pH (pH < 5.0) and at low ionic strength conditions (IS = 0.01 M NaClO _4), whereas the uptake of U(VI) was dominated by surface precipitation at high pH conditions. Thereby nano-iron oxyhydroxides can be used as an efficient backfill materials for the in situ disposal of U(VI)-bearing contaminated groundwater.