Adsorption of Actinides

Shorttitle Humic Acid (HA) is an important constituent of soil organic matter which was the subject of several environmental studies. In this work the adsorption isotherms of Thorium(IV) and Uranium(VI) onto Azraq Humic acid (AZHA) were studied at different temperature and pH values. The results indicate that Thorium(IV) has higher adsorptivity than Uranium(VI). The increasing of pH resulted in higher adsorptivity of Actinides. In contrast to heavy metals and Lanthanides (entropy driven), the adsorption of Actinides on HA was found to be exothermic and so enthalpy driven. This leads to the hypothesis that Thorium(IV) and Uranium(IV) are encapsulated in the interior of HA helix with their water of hydration because the interior is full with water. However, heavy metals and Lanthanides are adsorbed on the exterior of HA helix.