Process flowsheet test of the i-SANEX process with CHON-compliant ligands in aqueous and organic phases

Abstract

We report the results of a “CHON-compliant” i-SANEX flowsheet test using a surrogate feed with process concentrations of 241Am (>1 g/L) and major lanthanide and fission product species in a 32-stage counter-current centrifugal contactor (CC) rig. By combining flowsheet modelling with experience from the European GENIORS project, a flowsheet was designed that included the lanthanide/actinide extraction, fission product scrubbing, actinide stripping and finally, lanthanide stripping; therefore, covering the entire flowsheet except solvent treatment. The extraction system was 0.2 M N,N,N′,N′-tetraoctyldiglycolamide (TODGA) in Isane-185 with 5 v/v.% 1-octanol as a phase modifier. Actinide stripping was afforded by the aqueous soluble pyridine-2,6-bis(1H-1,2,3-triazol-4-yl) (PTD), whilst the lanthanide stripping was performed by N,N,N′,N′-tetraethyldiglycolamide (TEDGA). This represents the first test of PTD and TEDGA across the full flowsheet using counter-current CC and with process concentrations of americium. This CHON-compliant i-SANEX flowsheet offers clear improvements to the reference process. The use of a full PUREX raffinate simulant as the feed for the process has also permitted the measurement of concentration profiles of many species that are not normally followed in such detail. This has highlighted that under the conditions used – 8 stages of extraction, 8 stages of scrubbing (0.7 M HNO3) – some of the lanthanides recycle and do not reach steady-state in the timeframe of the experiment. Overall, the flowsheet demonstrated good control of 241Am with 98.6 % being routed to the actinide product although further work is needed to fully control some lanthanides and fission products, including; La, Ce, Pr, Gd, Tc, Ru and Sr.