Synthesis and Characterization of a Bentonite-Alginate Microspherical Adsorbent for Removal of Uranyl Ions from Aqueous Solutions

A novel microspherical adsorbent for the removal of uranium from aqueous solutions was developed by immobilizing of natural bentonite in the polymeric matrix of calcium alginate. Different uptake properties of the prepared microspheres were examined using batch, stirred and column methods. The adsorbent showed high affinity toward uranium ions, especially at pHs above 3. Major uptake mechanisms included ion exchange, chelating of the (UO2)(2+) ions to the -OH groups of alginate, and surface complexation with bentonite. Surprisingly, the capacity of microspheres was higher than both its constituents, revealing that a synergetic effect occurs. Adsorption kinetics was controlled by slow chemical reaction of UO22+ ions with bentonite, and it obeyed a shrinking core model. Also a pseudo-second order chemical reaction fairly fitted the kinetics data. The synthesized microsphrese, in addition to cost efficiency, showed a relatively good column performance and high durability and reusability.