Interaction of humic acid and Am(III) in aqueous solution.

Abstract

Laboratory experiments using radiotracer of americium (241Am) and humic acid isolated from natural surface soil have been conducted to evaluate the effect of added humic acid on the behavior of Am(III) in aqueous solution and the stability constant of the complex formed between Am(III) and humic acid. The former experiments were performed in the synthetic aqueous medium containing Ca or in fresh rain water at pH 6.5 and 4.5. At pH 6.5 in the absence of humic acid, Am(III) in both solutions [(Ca: 10 ppm) or rain water] was almostly adsorbed on the wall of the polyethylene vial used, and the major fraction of Am left in the solution was retained on the filter of 0.45μm pore size. On the other hand, in the presence of humic acid (100 ppm), the adsorption of Am on the vail was not observed, and the decrease of the retention of Am on the same filter suggests its complex formation with humic acid. At pH 4.5, the behavior of Am(III) in the solution (Ca: 10 ppm) was not influenced by the addition of humic acid (100 ppm). When the quantities of Ca were increased in the solution at a constant amount of humic acid, insoluble complexes were formed according to the increase of Ca to humic acid, and Am was scavenged over 90% as the insoluble complexes. The study of stability constant indicated that Am(III) had the strong interaction with humic acid.