Competitive Distribution of Europium and Samarium Based on Reaction Rate-Limiting Process in Nitrilotriacetamide Extractant-Impregnated Polymer-Coated Silica Particles

Since in the nuclear fuel cycle, multiple lanthanide and actinide ions are separated by chromatography, understanding the mass transfer mechanism in the solution with multiple ions, which is generally difficult, is important for effective separation. In the present study, we have elucidated the mass transfer mechanism of Eu(III) and Sm(III) in a solution with these ions in single nitrilotriacetamide (NTA) extractant-impregnated polymer-coated silica particles. The rate-limiting process of mass transfer was the reaction of ions with NTA molecules, in which the NO3− ions were not involved, which was consistent with that obtained in a single ion distribution system. In a two-ion distribution system, the competitive reaction of Eu(III) and Sm(III) with NTA molecules was observed. The forward and backward reaction rate constants of Eu(III) and Sm(III) were determined to be \(k_{1}^{\text{Eu}}\) = (1.8 ± 0.7) × 102 M−2 s−1 and \(k_{ - 1}^{\text{Eu}}\) = (6.1 ± 5.3) × 10−4 s−1, and \(k_{1}^{\text{Sm}}\) = (1.9 ± 0.5) × 102 M−2 s−1 and \(k_{ - 1}^{\text{Sm}}\) = (5.8 ± 4.6) × 10−4 s−1. The obtained result indicates that in the near future the mass transfers of several ions in the particle can be analyzed with the present method.