COUNTER-CURRENT EXTRACTION OF NEPTUNIUM FROM SIMULATED PRESSURIZED HEAVY WATER REACTOR HIGH LEVEL WASTE USING N,N,N′,N′-TETRAOCTYL DIGLYCOLAMIDE

The extraction behavior of neptunium was investigated from Pressurized Heavy Water Reactor Simulated High Level Waste (PHWR-SHLW) using 0.05 M N,N,N',N'-tetraoctyl diglycolamide (TODGA) + 5% iso-decanol dissolved in n-dodecane as the extractant. Batch extraction data revealed that the extraction of Np(IV) was a magnitude of order higher than that of the Np(VI). The stoichiometry of the extracted species was investigated by slope analysis and was found to be 2:1 (Ligand : Metal) for Np(IV) and 1:1 for Np(VI). The distribution data suggested that the neptunium in SHLW was predominantly converted into Np(VI) and its extraction decreased. Counter-current extraction studies employing 12 stages of mixer settler suggested that similar to 97% extraction of Np was possible from PHWR-SHLW at organic-to-aqueous phase ratio (O/A) of 1. However, stripping was efficient and > 99.9% of Np could be back extracted in 8 stages from the loaded organic phase.