Comparison in the aggregation behaviour of amide extractant systems by dynamic light scattering and ATR-FTIR spectroscopy

Abstract

The aggregation behavior of N,N,N’,N’-tetraoctyldiglycolamide (TODGA) in n-dodecane was studied in the presence of two different phase modifiers, N,N-di-hexyloctanamide (DHOA) and 1-octanol using dynamic light scattering (DLS) spectroscopy. The results were compared with the aggregation behavior of a modifier free extractant system N,N-di-octyl-2-hydroxyacetamide (DOHyA) in n-dodecane. Aggregation studies were done as a function of concentration of nitric acid and Nd (III) ions in the aqueous phase. The size distribution of reverse micellar aggregates revealed different aggregation mechanisms in the presence and absence of phase modifiers. For TODGA-modifier systems, the sizes of reverse micellar aggregates were bigger than DOHyA and among the two phase modifiers studied, use of 1-octanol resulted in the formation of bigger aggregates compared to DHOA. The observations from DLS measurements were co-related with the results from ATR-FTIR spectroscopy for all the three extractant systems. The sizes of reverse micellar aggregates increased with increase in extraction of nitric acid and/or Nd (III) ions and no third phase was visible in all the three systems even under very high loading conditions. The aggregation studies under co-current extraction conditions from fast reactor simulated high level waste solution (FR-SHLLW) showed the formation of smaller reverse micellar aggregates and third phase or crud formation after 3–4 successive contacts for all the three systems.