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  • 1 Hikkaido University Graduate School of Engineering Kita 13 Nishi 8 Sapporo 060-8628 Japan
  • 2 Tohoku University Oarai branch, Institute for Materials Research Narita-machi Oarai-machi, Higashiibaraki-gun, Ibaraki 311-1313 Japan
  • 3 National Institute of Radiological Sciences Environment Radiation Protection Research Group, Research Center for Radiation Safety 3609 Isozaki Hitachinaka, Ibaraki 311-1202 Japan
  • 4 Ishikawajima-Harima Heavy Industries Co., Ltd Shin-Nakahara-cho 1 Isogo-ku, Yokohama 235-8501 Japan
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Abstract  

Complexation of Am(III) with humic acid was studied at various pHs in 0.1M NaClO4. The stability constants of the Am(III)—humate complexes were determined by a cation-exchange method. The values of log1 and log2 increased slightly with increases of pH from 4 to 6 and were found to be 6.9 and 11.6, respectively, at a pH of 5. Markedly larger values than these were obtained by a solvent extraction method. This discrepancy was also revealed by summarizing data from several literature sources. It is very likely that this can be ascribed to decreases in either humic acid and/or the extractant from the extraction system due to humate interactions at the aqueous-organic interface.