Evaluation of dinonyl phenyl phosphoric acid (DNPPA) and its synergistic mixtures with neutral oxodonors for extraction and recovery of uranium from nitric acid medium

The extraction behavior of uranium (VI) from nitric acid medium was investigated using dinonyl phenyl phosphoric acid (DNPPA: monomeric form (HA), dimeric form (H2A2)) as extractant either alone or in combination with neutral oxodonors (S) such as tri-n-butyl phosphate (TBP), tris(2-ethylhexyl) phosphate (TEHP), and Cyanex 923 (a mixture of four different trialkyl phosphine oxides) dissolved in n-paraffin. Indigenously synthesized DNPPA was purified by two routes namely (a) liquid–solid separation using neodymium salt, and (b) liquid–liquid separation using mono ethylene glycol. An attempt was made to compare different phosphoric acid extractants viz. di(2-ethylhexyl) phosphoric acid (D2EHPA), 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A), bis(2,4,4-trimethyl pentyl) phosphinic acid (Cyanex 272) vis-à-vis DNPPA, for the extraction of uranium from nitric acid medium. The effects of different experimental parameters such as aqueous phase acidity (up to 8 M HNO3), extractant and metal ion concentration etc. on uranium extraction were investigated. The presence of neutral oxodonors like TBP, TEHP, Cyanex 923 along with DNPPA showed synergistic enhancement in the extraction of U(VI) in the order: Cyanex 923 > TBP > TEHP. The stoichiometry of the extracted U(VI) species using synergistic mixtures conformed to UO2(HA2)2·2S. These studies suggest that binary mixtures of DNPPA and neutral donors can be applied for uranium recovery from nitric acid media.

► Extraction of U(VI) from nitric acid using DNPPA and other acidic extractants.
► DNPPA along with neutral oxodonors showed synergism in the uranium extraction.
► Synergistic mixtures can be useful for uranium recovery from waste solutions.