Selective and highly efficient removal of uranium from radioactive effluents by activated carbon functionalized with 2-aminobenzoic acid as a new sorbent

Abstract

The purpose of this study was modification of activated carbon (AC) to prepare a new selective sorbent for removal of uranium ion. The modification was performed by introducing carboxyl groups onto AC using ammonium persulfate (APS) in sulfuric acid solution followed by functionalization with 2-aminobenzoic acid (ABA) as a selective ligand for U (VI) ion (UO22+) adsorption. The characterization of the synthetized sorbent (AC-ABA) was carried out through several methods including potentiometry, scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction and FT-IR to confirm successful functionalization of the sorbent surface with oxygen and amine groups. The sorption of U (VI) on the unmodified AC and AC-ABA was investigated as a function of contact time, sorbent content, initial uranium concentration, solution pH, and temperature using batch sorption technique. In addition, the effect of various parameters on the U (VI) sorption capacity was optimized by the response surface methodology as a potent experimental design method. The results indicated that sorption of U (VI) under the optimal conditions was significantly improved onto AC-ABA compared to AC. Kinetic studies displayed that the sorption process reached equilibrium after 100 min and followed the pseudo-second-order rate equation. The isothermal data fitted better with the Langmuir model than the Freundlich model. The maximum sorption capacity of AC-ABA for U(VI) was obtained to be 194.2 mg g−1 by the Langmuir model under optimum conditions, which demonstrates the sorption capacity has been improved by the modification process. The thermodynamic parameters (ΔH, ΔS and ΔG) indicated that sorption of uranium onto AC-ABA was an endothermic and spontaneous process. The sorption studies on radioactive effluents of the nuclear fuel plant represented high selectivity of AC-ABA for removal of uranium in the presence of other metal ions, and the selectivity coefficients significantly improved after modification of the sorbent. Application of AC-ABA for treatment of industrial effluents containing heavy and radioactive metal ions show high potential and capability of the proposed method.