The extraction of hexavalent uranium from nitric acid solutions by tri- n-dodecylamine nitrate

Abstract

Solutions of tertiary amines nitrates behave like liquid anion exchangers in the extraction of uranyl nitrate from aqueous solutions. The extraction mechanism is based on the formation of anionic uranium complexes in the aqueous phase which undergo extraction: ▪ The uranium partition coefficient increases at increasing nitric acid molarities in the aqueous phase, reaches a maximum at approximately 6 M HNO 3, then decreases. This behaviour is explained as due to the presence of different types of uranium complexes in the aqueous phase. Below 6 M HNO 3 the extractable species UO 2(NO 3)↓ +n n− is predominating; above 6 M HNO 3 the inextractable HUO 2(NO 3) 3 complex prevails as indicated by absorption spectra and ion exchange behaviour. Different values of n, ranging from 1 to 1·7 were found depending on salting strength, uranium and nitric acid concentration. The influence of the organic phase composition was studied by directly dissolving solid uranyl nitrate in the amine solvent. No difference was detected in the absorption spectra and ion exchange behaviour between the uranium loaded organic phase obtained by extraction and the one obtained by solid UNH solubilization. Results of solubility experiments seem to exclude an extraction mechanism based on the stepwise complex formation of an amine polinitrate.