Nitric acid extraction with monoamide and diamide monitored by second harmonic generation at the water/dodecane interface

The interfacial properties of the DEHiBA and DMDBTDMA extractant molecules used in the nuclear industry are examined to obtain a better understanding of ion transfer across the water/oil interface. Optical second harmonic generation (SHG) is used in combination with bulk nitric acid titration and interfacial tension (IFT) measurements. First, the amphiphilic properties of both extractant molecules are characterized by static IFT. Second, real time SHG experiments and titration are carried out to follow the kinetics of nitric acid extraction. The SHG intensity evolution is strongly dependant on the extractant concentration in the organic phase and the SHG intensity fluctuations are correlated with the nitric acid flux across the interface. It suggests that these intensity fluctuations are the signature of a strong modification of extractant concentration at the interface that is maximal close to a critical aggregation concentration of extractant in the organic phase.