Extraction of long-lived radionuclides from nitric acid solutions using an extractant based on dibutyl hydrogen phosphate and chlorinated cobalt dicarbollide

Research paper by S. A. Rodionov, A. N. Viznyi, V. M. Esimantovskii, B. Ya. Zilberman

Indexed on: 08 Jan '09Published on: 08 Jan '09Published in: Radiochemistry


Chlorinated cobalt dicarbollide (CCD), when added to concentrations of 0.25 M to a solution of dibutyl hydrogen phosphate (HDBP) in m-nitrobenzotrifluoride (MNBTF), increases the distribution ratios of trace amounts of Eu and Am without changing the slope (tan α ∼ 2) of their dependences on HDBP concentration in the 0–1.5 M range. At [CCD]/([CCD] + DBPA]) = 0.2–0.22, the synergistic effect is observed in the entire range of HDBP concentrations in extraction of these elements from 1.0 and 2.5 M HNO3. In this case, HDBP suppresses the extraction of Cs with CCD in the area below the synergistic maximum, where antagonism is observed in the extraction of Cs. Polyethylene glycol (PEG, Slovafol-909) was added to the extraction mixture to improve the extraction of Sr. The extremum is attained at its concentration in the solvent with HDBP of ∼0.033–0.065 M, which is smaller than that in the absence of HDBP by a factor of 1.5–2.5. With increasing concentration of HDBP in the HDBP-CCD-PEG-MNBTF extraction system, the slopes for Eu and Am are 1.3 and 0.6, whereas the slopes for Cs and Sr decrease nonlinearly and amount to −1.8 and −1.3, respectively. With increasing concentration of HNO3, D for Eu, Am, and Cm decreases in proportion to the HNO3 concentration to the power of −3 irrespective of the PEG concentration, and for Cs and Sr, to the power of −2 in the presence of PEG, whereas in the PEG-free systems the dependences are nonlinear. The synergistic extractant is characterized by higher (by an order of magnitude) solubility of metal solvates as compared to the HDBP-MNBTF system (concentration of Eu in the extractant >0.163 M). The extractant containing HDBP (1.1 M), CCD (0.23 M), and Slovafol-90 (0.065 M) in MNBTF is suggested for combined recovery of rareearth (REE) and transplutonium elements (TPE) and of Cs and Sr from high-level waste (HLW) after reprocessing of spent nuclear fuel (SNF) with high burn-up.