Insights into the Third Phase Formation Behaviour of N,N ‐Didodecyl‐ N’,N’ ‐Dioctyl Diglycolamide in n ‐Dodecane Investigated by Dynamic Light Scattering and FTIR Spectroscopy

Abstract N , N ‐didodecyl‐ N ’, N ’‐dioctyl diglycolamide (D 3 DODGA) was regarded as a promising ligand for the extraction of trivalent lanthanides and actinides from nuclear waste, owing to the absence of undesirable third phase formation during liquid‐liquid extraction. However, the reason for the absence of third phase formation in D 3 DODGA as compared to other diglycolamides was not known. To unravel the absence of third phase formation, the extraction behaviour of nitric acid and Nd(III) in 0.2 M D 3 DODGA in n ‐dodecane ( n ‐DD) was studied and the reverse micellar aggregation behaviour of the organic phase was probed by dynamic light scattering (DLS) and FTIR spectroscopy. The results were compared with those obtained in popular ligands abbreviated as TODGA, TEHDGA and TDdDGA in n ‐dodecane under similar conditions. The limiting reverse micellar aggregate size for third phase formation was determined to be 11.6 nm at the limiting nitric acid concentration of 0.54 M in organic phase. The investigations revealed that the absence of third phase in D 3 DODGA and TDdDGA was due to the presence of long chain dodecyl group attached to the molecule, as compared to the octyl moiety present in TODGA and TEHDGA. As a result, it was possible to load higher concentration of nitric acid or Nd(III) in D 3 DODGA without the problem of third phase formation. In view of this, the D 3 DODGA in n ‐DD can be employed efficiently for the separation of trivalent actinides and lanthanides from nuclear waste.