KINETIC STUDIES ON THE SOLVENT EXTRACTION OF URANIUM(IV)AND THORIUM(IV) FROM NITRIC ACID SOLUTION WITH TRIBUTYL PHOSPHATE

The kinetics of extraction of uranium(Ⅳ)and thorium(Ⅳ)from nitric acid solution by tributyl phosphate(TBP)in kerosene has been investigated using single drop technique.The extraction rate of uranium(Ⅳ)and thorium(Ⅳ)increases with increasing nitric acid concentration and with saturation appearing at nitric acid concentration higher than about 2.0 mol/L. The rate increases linearly with NO3- ion concentration,but decreases with H+ ion concentration. The rate equations of uranium(Ⅳ)and thorium(Ⅳ)at constant concentration of nitric acid were obtained as follows:RU = Ku[U(Ⅳ)][TBP](o);RTh = KTh[Th(Ⅳ)][TBP](o)The rate of uranium(Ⅳ)and thorium(Ⅳ)increases with increasing temperature,rate increasing in lower temperature range being faster than in higher temperature range. Based on the data in less than 30°C, linear regression analysis of in Ku and ln KTh vs 1/T shows the apparent activation energy of 16kJ/mol for uranium (Ⅳ)and 43 kJ/mol for thorium(Ⅳ). It suggests that the extraction rate of uranium (Ⅳ)and thorium(Ⅳ)is controlled by chemical reaction at lower temperature and by diffusion process at higher temperature.