Solvent effects on the extraction rate in proposed GANEX processes
Paper in proceeding, 2011
A group actinide extraction process (GANEX) for reprocessing of used nuclear fuel has earlier been presented using the diluent cyclohexanone and combining the extractant molecules tri-butyl phosphate (TBP) and 6,6’-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4] triazin-3-yl)-[2,2’]bipyridine (CyMe4-BTBP). This GANEX process shows high potential for the separation of trivalent actinides from trivalent lanthanides. In order to improve this process an alternative solvent has been recently presented where the TBP molecule is replaced with a mono-amide ligand, di(2-ethylhexyl) butyramide (DEHBA). One of the advantages with the amide is that it is has previously shown good extraction of uranium and plutonium.
One important step in the evaluation and comparison of these two proposed processes is the rate of the extraction. The GANEX solvent using TBP has in this paper been shown to have a faster mass transfer than the solvent containing DEHBA. This is explained with the surfactant property of the TBP molecule. This property makes the surface to volume ratio during mixing higher in the TBP based solvent. However, from this investigation, no conclusion can be drawn whether the rate determining step of the extraction is the diffusion or the chemical reactions taking place. To achieve this information more research is needed.