Complexation of Eu3+ and Am3+ with soil humic acid extracted from Okchon Basin of Korean Peninsula

The complexation of Eu³⁺ and Am³⁺ ions with the humic acids has been investigated at various pH (4.0, 4.5, 5.0, 5.4) in 0.1M NaClO₄ solution using solvent extraction technique. Two humic acids are used in this study: humic acid extracted from the soil of Taejon on the Okchon Basin of Korea (TJHA) and commercially available one from Aldrich Chemical Co. (AHA). The total carboxylate group concentrations were determined to be 3.58 meq/g and 4.59 meq/g for Taejon and Aldrich humic acids, respectively. The conditional stability constants (log ₁ and log ₂), dependent on the pH of the solution, of the complexes of Eu³⁺ and Am³⁺ ions with the humic acids have been determined at the ionic medium of 0.1M NaClO₄. The values of stability constants with the degree of ionization of TJHA for Eu and Am complexes are quite well agreed with those of Lake Bradford humic acid (LBHA), indicating that structural characteristics of TJHA and LBHA may be quite similar to one another.