Solvent extraction method for transuranium element

In a solvent extraction method for recovering transuranium (TRU) elements using high-level liquid wastes of spent nuclear fuels, TBP (tri-n-butyl phosphate) and CMPO (octyle (phenyl)-N, N-diisobutylcarbamoylmethyl-phosphine oxide), a solvent containing TBP and CMPO is mixed with liquid wastes to which a carboxylic acid having a chelate forming effect is added. This method suppresses extraction of Zr and Mo in the liquid wastes and can efficiently recover actinoids such as TRU elements (U, Am, Cm, Pu or Np) at a high purity from an organic phase after mixing and settling. The amount of expensive solvents to be used can be reduced without forming a third phase by setting the ratio between the organic phase and the aqueous phase to 2.3 to 2.6. (T.M.)