Adsorption of uranium in the presence of different ions, humic acid and effect of thorium on uranium adsorption by activated carbon

In this study, rice straw-based carbon was prepared and then modified by two acidic and basic oxidizing agents. One oxidized by HNO3, labeled as RSN, and other oxidized by KOH labeled as RSK. The modified carbons (RSN and RSK) were tested in two single-component systems: Removal of U(VI) using RSK and Th(IV) using RSN. Factors affecting U(VI) in three multi-component systems were examined: (i) Co-existing anions and cations, (ii) co-existing Th(IV), and (iii) presence of humic acid (HA). In this concern, different cations under investigation have marginal effect on the adsorption of uranium, except in case of iron ion. Co-existing of iron ions at high levels may compete strongly for the adsorption sites with uranium ions, resulting in a substantial reduction of uranium removal. The prepared carbon showed good selectivity in extracting uranium even in the presence of relatively high concentrations (100 mg/l) of anionic complexing agents and common electrolyte species. In case of multi-component system U(VI)/Th(IV), the capacity of each metal was reduced due to the competition between two ions for sorption sites on carbon surface. In presence of HA, the metal-humic interactions play a very important role in determining the extent of adsorption. It is concluded that multi-species adsorption can be significantly affected by adsorbate interactions and the understanding of these interactions needs great attention in adsorption study in the future.