Separation process between lanthanide element and transplutonium element by solvent extraction

It has been found that only the transplutonium element (TPE) can be extracted even an acidic solution at a high separation rate by using a combination of an N-heterocyclic compound and anions having high hydrophobic property as an extraction solvent. Then in the present invention, the N-heterocyclic compound and the hydrophobic anions are dissolved in an organic solvent, and it is brought into contact with an aqueous acidic solution containing lanthanide element (RE) and TPE under stirring. As a result, only the TPE is extracted to an organic phase, and most of the RE remains in an aqueous phase. In the present invention, one or more of RE may be dissolved in the aqueous acidic solution. In the same manner one or more of TPE may be dissolved in the aqueous acidic solution. With such procedures, TPE can be separated and recovered at high purity and high yield by continuous extraction steps using a counterflow multi-stage extractor. (T.M.)