CTAB-bentonite improved U(VI) adsorption in the presence of U(VI)-CO3 complexes. High dissolved carbonate concentration decreased the U(VI) adsorption capacity. The factors effect on U(VI) adsorption by CTAB-bentonite were studied. U(VI) adsorption capacity correlated with the proportion of aqueous U(VI) species. U(VI)–CO3 complexes were mainly adsorbed by anion exchange on CTAB-bentonite.