Extractant separation in DIAMEX-SANEX process

In the frame of the French radioactive waste management acts of December 1991 and June 2006, separation processes for minor actinide selective recovery have been developed to significantly decrease the radiotoxicity of the ultimate waste produced by the nuclear industry. Several routes are envisaged for actinide/lanthanide separation, either in two cycles, using two different solvents (generally a DIAMEX followed by a SANEX process), or in one single cycle involving the same solvent during the whole process. The DIAMEX-SANEX concept described in this paper is new concept: the organic phase, which consists of a cationic exchanger (phosphorus acid) and the malonamide developed for the DIAMEX process (N,N'-dimethyl-N,N'- di-octyl-hexyl-ethoxy-malonamide named DMDOHEMA), is split at a given stage of the process to avoid interactions between these two extractants during the co-extraction step of actinides and lanthanides. This paper describes some results obtained with di-n-hexyl phosphoric acid (HDHP), which fulfills the required criteria for process development. For instance, this reagent can easily extract lanthanides from a weak acidic aqueous solution, and it can be selectively separated from DMDOHEMA, thanks to a basic solution. (authors)