Studies on the Use of N,N,N ',N '-Tetra(2-ethylhexyl) Diglycolamide (TEHDGA) for Actinide Partitioning. I: Investigation on Third-Phase Formation and Extraction Behavior

Diglycolamides have emerged as an interesting class of extractants for actinide partitioning from high-level waste (HLW). N,N,N',N'-tetraoctyl diglycolamide (TODGA) has been extensively studied for lanthanide-actinide co-extraction behavior. The present work deals with a branched isomer of TODGA, that is, N,N,N',N'-tetra(2-ethylhexyl)diglycolamide (TEHDGA). TEHDGA was studied for the extraction of Am-241 and third-phase formation. The effect of using different phase modifiers on the prevention of the formation of a third phase during nitric acid extraction by TEHDGA along with the acid uptake behavior by TEHDGA in the presence of the modifiers was studied. The modifiers used for this purpose were di(n-hexyl)octanamide ( DHOA), isodecanol, and n-decanol. The effect of the modifiers on the uptake of Am-241 as a function of acid concentration and as a function of modifier concentration was also examined. DHOA was found to be a suitable modifier, in spite of its high acid uptake. The uptake of lanthanides Ce, La, Eu, Gd, and Nd and elements such as Fe, Ni, Mn, Mo, Ru, Sr, and Cs with DHOA-modified TEHDGA-n-dodecane solvent systems were investigated. The results obtained indicated that, while DHOA-modified TEHDGA/n-dodecane extracted lanthanides and actinides, it did not show any significant uptake of other elements. Thus, the TEHDGA-DHOA/n-dodecane solvent system can be used effectively for the partitioning of lanthanides and actinides from HLW.