Kinetic Mass Transfer Behavior of Eu(III) in Nitrilotriacetamide-Impregnated Polymer-Coated Silica Particles

We investigated the distribution mechanism of Eu(III) in a single polymer-coated silica particle including nitrilotriacetamide (NTA) extractants known as HONTA and TOD2EHNTA. We studied the kinetic rate constants of the distribution process at various concentrations of NO3− (CNO3−) that were prepared using HNO3 and NaNO3 solutions. The rate-determining process during the distribution of Eu(III) was identified as the reaction process of Eu(III) for both extractants, that is, the reaction process of Eu(III) and two NTA molecules in the polymer layer of the silica particle. Furthermore, the reaction of Eu(III) with NO3− ions was found not to be involved in the rate-determining process. The forward (k1) and backward (k−1) reaction kinetic constants for the reaction between Eu(III) and two NTA molecules were determined to be k1 = (5.7 ± 2.2) × 102 M−2 s−1 and k−1 = (2.3 ± 4.4) × 10−4 s−1 for HONTA, and k1 = (6.5 ± 3.0) × 102 M−2 s−1 in the NaNO3 system and k−1 = (2.0 ± 1.5) × 10−4 s−1 in both solutions for TOD2EHNTA. The present study provides a valuable approach for the evaluation and enhancement of the functionality of ‘single extractant-impregnated polymer-coated silica particles’.