Single-cycle separation of americium (III) from simulated high-level liquid waste using tetra-bis(2-ethylhexyl)diglycolamide and bis(2-ethylhexyl)phosphoric acid solution

The extraction behavior of Am(III) and various metal ions present in the fast reactor simulated high-level liquid waste (FR-SHLLW) was studied in 0.1 M tetra-bis(2-ethylhexyl)diglycolamide (TEHDGA) and 0.25 M bis(2-ethylhexyl)phosphoric acid (HDEHP) extractants in n-dodecane to develop a single-cycle process approach for the separation of Am(III) from HLLW. The extraction of Am(III) was accompanied by the co-extraction of lanthanides and unwanted metal ions such as Zr(IV), Mo(VI), Y(III), Fe(III) and Pd(II). A procedure was developed to minimize the extraction of unwanted metal ions by using aqueous soluble complexing agents in FR-SHLLW. Based on these studies, a counter current mixer-settler run was performed to separate Am(III) from FR-SHLLW as well as from lanthanides, using a 16-stage mixer-settler. Quantitative extraction of Am(III), Ln(III), Y(III), and Mo(VI) in 0.1 M TEHDGA-0.25 M HDEHP/n-DD was observed. About 80% of Fe(III) was co-extracted into the organic phase. The recovery of Am(III) from the loaded organic phase was carried out by using 0.05 M diethylenetriaminepentaacetic acid–0.5 M citric acid at pH 3. The stripping of Am(III) was quantitative. However, the americium product contained about 10–20% of lighter lanthanides i.e. lanthanum to neodymium, perhaps due to the presence of these lanthanides in high concentration in FR-SHLLW. The study, thus, indicated the possibility of separating Am(III) from FR-SHLLW, which contained chemically similar lanthanides and several other metal ions in a single-cycle processing step.