Understanding of uranium extraction mechanisms from phosphoric and sulfuric media using DEHCNPB

The extraction of uranium(VI) from phosphoric and sulfuric acid solutions using DEHCNPB (butyl-1-[N,N-bis(2-ethylhexyl)carbamoyl]nonyl phosphonic acid) was studied to understand the influence of the original acidic medium on uranium extraction (phosphoric acid 5 mol/L or sulfates 1.6 mol/L at pH=1). Uranium(VI) extraction isotherms highlight different extraction behaviors depending on the initial medium with a lower [DEHCNPB]/[U] ratio reached at saturation with the phosphoric medium. Slope analysis showed different average stoichiometries: 1.9 and 3.3 for the phosphate and sulfate experiments respectively. The co-extraction of water with uranyl was evidenced by Karl-Fischer titrations and ESI-MS measurements and ESI-MS analysis confirmed the presence of uranyl/DEHCNPB complexes with one molecule of water, probably in the first coordination sphere. (author)