MODELING EXTRACTION OF URANYL NITRATE, NITRIC ACID AND WATER BY TRIBUTYL PHOSPHATE

摘要

The model developed by Naganawa and Tachimori (H. Naganawa, S. Tachimori, Bull. Chem. Soc. Jap. 70, 809, (1997)) was extended to describe extraction equilibria between aqueous phases containing uranyl nitrate and nitric acid contacted with tributyl phosphate (TBP) in dodecane. The introduction of 6 complexes allows one to describe extraction data for the three components (water, nitric acid and uranyl nitrate) in the case of an organic phase composed of 30% in volume of TBP at 25°C. The thermodynamic activities of the components in the aqueous phase were obtained using the extended Pitzer expression. This method gives a good representation of the osmotic coefficient for pure binary aqueous solutions of uranyl nitrate and nitric acid up to 4 mol L~(-1) and 10 mol L~(-1), respectively. The stoichiometries of the complexes in organic phase were obtained one by one, by an optimisation procedure. The present treatment suggests the formation of complexes containing 2 and 3 TBPs for 1 uranyl nitrate.