Immobilization and recovery of uranium(VI) using Na-bentonite from aqueous medium: equilibrium, kinetics and thermodynamics studies

Abstract

To better assess the environmental behavior and effect of uranium on living organisms more accurately, herein, Na-bentonite was used as an adsorbent for the immobilization of uranium from radionuclide polluted wastewater. The experimental results demonstrated that sorption dynamics of U(VI) on the Na-bentonite could obtain equilibrium in a time period of 10h. The sorption performance of U(VI) on the surface of Na-bentonite material was strongly dependent on pH values of solution. The sorption of U(VI) was influenced by ionic strength at pH<7.5, whereas was independent of ionic strength at pH>7.5. The presence of fulvic acid (FA) or humic acid (HA) promoted the sorption behavior of U(VI) onto Na-bentonite at low pH values while suppressed the sorption performance at high pH values. The thermodynamic coefficients (i.e., ΔS0, ΔG0 and ΔH0) calculated from the temperature-dependent sorption isotherms illustrated that sorption process of U(VI) on the Na-bentonite was spontaneous and endothermic. At low pH values, the sorption performance of U(VI) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on Na-bentonite surfaces, whereas inner-sphere surface complexation and co-precipitation were the main sorption mechanism at high pH values. Considering its high physicochemical stability and high removal performance property, the prepared Na-bentonite can be used as a cost-effective and potential adsorbent for the immobilization and recovery of U(VI) from large volumes of aqueous solutions.