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

The influence of U(VI)-CO3 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 (qe) 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 UO2(CO3)34 −, UO2(CO3)22 −, (UO2)2CO3(OH)3−, UO2(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)-CO3 complexes adsorption capacity correlated with the proportion of aqueous U(VI) species and the competitive adsorption between CO32- anions and U(VI)-CO3 complexes. Additionally, desorption results revealed that the most effective desorption agent was 1.0 mol/L HNO3 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.