Adsorption and migration of 241Am in aerated zone soil

Abstract

As an important radioisotope in nuclear industry and other fields, 241 Am is one of the most serious contamination concerns due to its high toxicity and long half-life. In order to supply useful reference for disposal of 241Am waste with low-medium radioactivity, the adsorption and migration behavior of 241Am on aerated zone soil were investigated by the static experimental method and column experiments. The results showed that more than 98% of the total 241Am could be adsorbed from 241Am solution of 0.32·10−7−1.1·10−7 mol/l by the soil at pH 4–9. The adsorption of 241Am on the soil was a pH-dependent process at pH 4, the adsorption rate of 241Am on the soil changed minutely. The adsorption equilibrium was achieved within 24 hours and no significant effect on adsorption of 241Am was observed at liquid-solid ratios of 50:1–500:1. The relationship between concentration of 241Am and adsorption capacities of 241Am can be described by the Freundlich adsorption equation. Adsorption of 241Am on the soil can be inhibited by humic acid, ferric hydroxide colloid, or some anions, such as citric acid anion, saturated EDTA solution, C2O4 2− and CO3 2−. It was also noted that the adsorption rate of 241Am drops in solutions containing Eu3+ or Nd3+, even 0.5 times above the 241Am concentration. A migration distance of 8 mm for 241Am(III) is observed only in the aerated zone soil containing ferric colloid, while a migration distance of less than 2 mm is noted in other soil samples after more than 250 days. All these results indicate that the aerated zone soil is an efficient sorbent for 241Am and can inhibit the migration of 241Am.