Effect of pH, ionic strength and humic acid on the sorption of uranium(VI) to attapulgite

Attapulgite was investigated to remove UO22+ from aqueous solutions because of its strong sorption capacity. Herein, the attapulgite sample was characterized by Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD) and acid-base titration in detail. Sorption of UO22+ on attapulgite was strongly dependent on pH values and ionic strength. The presence of humic acid enhanced the sorption of UO22+ on attapulgite obviously because of the strong complexation of humic acid (HA) with UO22+ on attapulgite surface. Sorption of UO22+ on attapulgite was mainly dominated by ion-exchange or outer-sphere complexation at low pH values, and by inner-sphere complexation at high pH values. The results indicated that attapulgite was a suitable material for the preconcentration and solidification of UO22+ from large volume of solutions because of its negative surface charge and large surface areas.