Impact of environmental conditions on the sorption behavior of U[O.sub.2.sup.2+] onto attapulgite studied by batch experiments

The sorption of U[O.sub.2.sup.2+] from aqueous solution on attapulgite was investigated as a function of contact time, solid content, pH, ionic strength, foreign ions, humic acid (HA), and fulvic acid (FA) under ambient conditions by using batch technique. The attapulgite sample was characterized by XRD and FTIR in detail. The results indicated that the sorption of U[O.sub.2.sup.2+] was strongly dependent on pH and ionic strength. The sorption of U[O.sub.2.sup.2+] on attapulgite increased quickly with rising pH at pH < 6.5, and decreased with increasing pH at pH > 6.5. The presence of HA or FA enhanced the sorption of U[O.sub.2.sup.2+] on attapulgite obviously at low pH because of the strong complexation of surface adsorbed HA/FA with U[O.sub.2.sup.2+] on attapulgite surface. Sorption of U[O.sub.2.sup.2+] on attapulgite was mainly dominated by ion-exchange or outer-sphere surface complexation at low pH values, but by inner-sphere surface complexation at high pH values. The results indicate that attapulgite is a very suitable adsorbent for the preconcentration and solidification of U[O.sub.2.sup.2+] from large volumes of aqueous solutions because of its negative surface charge and large surface areas. Keywords U[O.sub.2.sup.2+] * Attapulgite * Sorption * pH * Foreign ions * Humic acid * Fulvic acid