The U(VI) sorption on the bentonite modified by hexadecyltrimethylammonium bromide (HDTMA) was studied in the concentration range: 0.0001-0.001 mol/dm(3) in the aqueous phase and in the pH range: 3-10. The experiments concerning the pH influence on the molar absorption coefficient c(b) of U(VI) in the bentonite phase showed that the species: UO22+, UO2(OH)(+), UO2(OH)(2) UO2(OH)(3), UO2(OH)(4)(2), (UO2)(3)(OH)(5)(+), (UO2)(3)(OH)(7), present in the aqueous phase, are responsible for uranium sorption. Their sorption parameters K were determined and it is evident that for higher concentrations of HDTMA(+) cations in the bentonite phase, i.e. for b96-b157 bentonite, the presence of anionic species: UO2(OH)(3), UO2(OH)(4)(2), and (UO2)(3)(OH)(7) in the aqueous phase results in the increase of U(VI) molar absorption coefficient cb in the sorbent phase. (C) 2009 Elsevier B.V. All rights reserved.