Extraction of Am(III) and Eu(III) by 2-substituted benzimidazoles

Neutral 2-(N-hetarenyl)benzimidazoles (B) can extract Am(III) with appreciable selectivity over Eu(III), forming in the organic phase complexes of the type MA(3).nB (M = Am or Eu, A = anion of an acid HA and n = 1 - 3). The extractant properties of 2-(2-pyridyl)benzimidazole are improved by placing a methyl group into the 6-position, but little further improvement is achieved by the introduction of an another methyl group into the 5-position. Low extraction efficiency and deteriorated separation ability is exhibited by 2-(6-methyl-2-pyridyl)benzimidazoles. The efficiency of 6-methyl-2-(2-pyridyl)benzimidazole in the Am(III)/Eu(III) separation decreases in the anion sequence thiocyanate > nitrate similar to perchlorate similar to iodide > thenoate > 2-(2-pyridylazo)-1-naphtholate. Generally, the separation efficiency is suppressed by those factors which lower the average solvation number of the extracted complexes of Am(III).