Extraction of Actinide Elements by Trilaurylammonium Nitrate Carboxylic Acid Mixtures and Applications

The addition of pelargonic, capric, α-bromocapric, α-fluorocapric, and 3-fluorobenzoic acids to organic trilaurylammonium nitrate solutions significantly modifies the extraction of U(VI), Np(IV), and Pu(IV). Antagonism appears at strong nitric acidities, while enhancement of the extraction of U(VI) and Pu(IV) is observed at weak acidities. The antagonism observed is due to the formation of addition compounds between trilaurylammonium nitrate (R₃NHNO₃) and carboxylic acids (HA) = for pelargonic and capric acids, and for α-bromocapric, α-fluorocapric, and 3-fluorobenzoic acids. Extraction of UO₂²⁺, Am³⁺, Th⁴⁺, Np⁴⁺, and Pu⁴⁺ by capric, α-bromocapric, and 3-fluorobenzoic acids showed that the extractive power of these carboxylic acids is inadequate for the observation of extraction enhancement. The study of the organic phase by the measurement of nitric acid displacement and by dielectric method shows that trilaurylamine and carboxylic acids react to give the compounds (pelargonic and capric acids) and (α-bromocapric and 3-fluorobenzoic acids). The formation of trilaurylammonium carboxylates is responsible for extraction enhancement. Thus, in the case of U(VI), the compounds formed in the organic phase are (HA = capric acid) and (HA = α-bromocapric and 3-fluorobenzoic acids). The antagonisms observed were successfully exploited to resolve certain problems:

1. improvement of the reductive reextraction rate of plutonium under the action of pelargonic and capric acids in the process flowsheet for irradiated ²³⁷Np targets
2. reextraction of U(VI) and Np(IV) from organic trilaurylammonium nitrate or tributyl-phosphate solution under the action of α-bromocapric acid toward aqueous nitric solutions.