The distribution behavior of uranium and thorium has been investigated in a biphasic system of different aqueous nitric acid
concentrations and a solution of tris(2-ethylhexyl) phosphate (TEHP) inn-dodecane at 25°C. The effect of different uranium and thorium concentrations in the aqueous phase on the extraction of these
metal ions is evaluated. These results indicate that TEHP is a better choice than tri-n-butyl phosphate (TBP) for the separation of233U from the irradiated thorium matrix.