Comparison of U(VI) removal from contaminated groundwater by nanoporous alumina and non-nanoporous alumina

Abstract

In this study, the sorption and desorption of U(VI) from contaminated groundwater by nanoporous and non-nanoporous alumina were investigated under ambient conditions. The nanoporous and non-nanoporous alumina were characterized by XRD, specific surface area analysis, TEM and potentiometric acid–base titration. The nanoporous alumina exhibited high sorption capacity, large specific surface area, high surface acidity constants, low difference of surface acidity constants and high pH PNZC (point of net zero charge) due to the nanoporous effect. The worm-like shape nanoporous alumina was transferred into the floc-like shape gibbsite after the sorption in terms of TEM images. Sorption kinetics and sorption isotherms of U(VI) on both nanoporous and non-nanoporous alumina can be interpreted by pseudo-second order kinetic model and the Langmuir model, respectively. The sorption of U(VI) on nanoporous alumina is strongly dependent on pH and independent of ionic strength, whereas U(VI) sorption on non-nanoporous alumina is dependent on pH and ionic strength. The sorption mechanism is assumed to be mainly inner-sphere surface complexation for nanoporous alumina and outer-sphere surface complexation for non-nanoporous alumina. Approximately 100% of U(VI) was desorbed from non-nanoporous alumina while only ∼5% of U(VI) was extracted from nanoporous alumina when the concentration of NaHCO 3 was increased to 0.01 M in terms of sequential desorption experiments. The nanoporous alumina can be used as an efficient material for in situ immobilization of U(VI) from contaminated groundwater.