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 (D3DODGA) 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 D3DODGA 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 D3DODGA 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 D3DODGA 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 D3DODGA without the problem of third phase formation. In view of this, the D3DODGA in n‐DD can be employed efficiently for the separation of trivalent actinides and lanthanides from nuclear waste.

A multi-faceted approach to probe organic phase composition in TODGA systems with 1-alcohol phase modifiers

“…As the Ln-DGA complex C O frequency is red-shifted, this indicates a weaker C O bond associated with the Ln-DGA complex compared to the stronger C O bond in the (DGA)(HNO 3 ) 1-2 adducts. 33 This behavior is not isolated to the systems considered herein, but has been reported with DOHyA, 33 D 3 DODGA, 38 T2EHDGA, 39 TODGA, 33 TODGA (+DHOA), 40 TODGA (+1-octanol), 40 and TODGA (+DOHyA) 33 systems. These studies involved increasing the concentration of Nd at constant extractant and HNO 3 concentrations, where higher Nd concentrations resulted in larger Ds.…”

“…The systems that experienced a red-shi are consistent with the literature which explains this slight red shi to be the result of hydrogen bond interactions of HNO 3 molecules interacting with polar carbonyl group of TODGA, forming (DGA)(HNO 3 ) 1-2 adducts. 30,37,38 Across the varying alkyl chain lengths of 1-alcohol, the trend in this red-shied C]O frequency for 5 vol% is 1-hexanol < 1-octanol < 1-decanol. Increasing the 1-alcohol concentration to 30 vol% results in the reverse trend, 1-decanol < 1-octanol < 1-hexanol.…”

Synthesis and evaluation of new modified diglycolamides with different stereochemistry for extraction of tri- and tetravalent metal ions

“…33,35 According to literature, DGAs can form inverse micelles with polar molecules (e.g., HNO 3 ) in long-chain alkane diluents (e.g., n-dodecane or n-octane). 33,36,37 Massey et al found that the addition of n-octanol reduced the degree of aggregation and hence reduced the degree of 3 rd phase formation. 34 In our experiments, even at 10 mol L À1 HNO 3 , no 3 rd phase formation was observed.…”

“…The steric hindrance from the substitution in the backbone seems to reduce the probability of increasing aggregate and cluster formation in solution, hence reducing the possibility of third-phase formation at high nitric acid concentrations. 33,34,37 Low distribution ratios are not necessarily a disadvantage, as for a process application it must also be possible to back-extract the desired metal ions from the loaded organic phase. Nevertheless, the distribution ratios of the ligands considered here are quite low at a ligand concentration of 0.1 mol L À1 for the trivalent metal ions and associated with high uncertainties.…”

“…, n -dodecane or n -octane). 33,36,37 Massey et al found that the addition of n -octanol reduced the degree of aggregation and hence reduced the degree of 3 rd phase formation. 34 In our experiments, even at 10 mol L −1 HNO 3 , no 3 rd phase formation was observed.…”