The removal of U(VI) from aqueous solution by oxidized multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWCNTs) have exhibited high sorption capacity for radionuclides due to the unique hollow structure and large surface area. In this study, surface properties of oxidized MWCNTs were characterized by using XRD, SEM, FTIR and potentiometric acid–base titration. The sorption of U(VI) on oxidized MWCNTs as a function of contact time, U(VI) concentration, pH, ionic strength, humic acid/fulvic acid (HA/FA) and carbonate was investigated by using batch technique. The removal of U(VI) by oxidized MWCNTs was strongly dependent on pH and ionic strength. The presence of HA/FA enhanced U(VI) removal on oxidized MWCNTs at low pH while inhibited U(VI) sorption at high pH. The mechanism of U(VI) sorption on oxidized MWCNTs was assumed to be cation exchange/outer-sphere surface complexation in acidic pH and to form precipitation under circum neutral conditions. The oxidized MWCNTs exhibit higher sorption capacity and stronger chemical affinity than pristine MWCNTs. ► The removal of U(VI) by oxidized MWCNTs is strongly dependent on pH and ionic strength. ► The negative effects of HA/FA and carbonate on U(VI) uptake are observed at high pH. ► The sorption of U(VI) on oxidized MWCNTs is dominated by outer-sphere complexation at low pH. ► The oxidized MWCNTs can be used as a promising backfill material in wastewater disposal.