U(VI) adsorption onto cetyltrimethylammonium bromide modified bentonite in the presence of U(VI)-CO3 complexes

Abstract The influence of U(VI)-CO 3 complexes on U(VI) adsorption onto cetyltrimethylammonium bromide (CTAB) modified bentonite was investigated using batch adsorption experiments to simulate the feasibility of CTAB-bentonite as an adsorbent for the uranium resources recovery. The adsorption capacity (q e ) decreased with increasing pH from 8.9 to 9.5 and dissolved carbonate concentrations, but was significantly improved after cation surfactant modification. The adsorption kinetics was depicted by the pseudo-second-order kinetic equation, where the nonlinear Langmuir and Freundlich models fitted well with the data of CTAB-bentonite. The calculated thermodynamic parameters suggested that the adsorption of U(VI) on material was a spontaneous and endothermic process. In particular, we determined that UO 2 (CO 3 ) 3 4 − , UO 2 (CO 3 ) 2 2 − , (UO 2 ) 2 CO 3 (OH) 3 − , UO 2 (OH) 3 − anions may have been adsorbed by anion exchange with bromide ion from the CTAB molecule at high CTAB loading levels according to the uranyl speciation calculations, whereas U(VI)-CO 3 complexes adsorption capacity correlated with the proportion of aqueous U(VI) species and the competitive adsorption between CO 3 2– anions and U(VI)-CO 3 complexes. Additionally, desorption results revealed that the most effective desorption agent was 1.0 mol/L HNO 3 solution. The findings reported in this study aid in facilitating the extraction of uranium resources from aqueous using CTAB-bentonite and other possible clays, especially from salt lake brines or seawater and the consideration of practical U(VI) species in the natural environment.