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DIDPA [5] (see Figure II.3) processes. For both processes the MAs and other elements are extracted
with an acidic organophosphorous extractant, di-2-ethyl-hexyl-phosphoric acid (HDEHP for
TALSPEAK) or di-isodecylphosphoric acid (DIDPA), and An(III)/Ln(III) partition is achieved by
selective stripping of An(III) from the loaded solvent with the help of aqueous stripping solutions
containing the following complexing agents: alcohol-carboxylic acid (traditionally lactic or glycolic
acids, or citric acid as proposed recently) and diethylenetriaminopentaacetic acid (DTPA). It is
generally believed that the selective stripping of Ans is due to the fact that An(III)/DTPA complexes are
more stable than the corresponding Ln(III) complexes.
Since HDEHP and DIDPA extractants are cation exchangers, the nitric acid concentration of
the HLLW to be treated must be drastically reduced. This can be done, for example, by denitration with
formic acid, as investigated by JAERI scientists [9]. A definite advantage of the DIDPA process
compared with TALSPEAK resides in the higher affinity of the extractant for the metal ions to be
extracted, so that they can be extracted from a more acidic aqueous solution (HNO 3 = 0.5 M) than in
the TALSPEAK process. The amount of secondary effluents is of the same order as the TRUEX
process.
Consequently, a major drawback of these processes, i.e. the precipitation of some FPs in the
form of hydroxides which can carry a fraction of the TRU present in the waste, can be minimised.
Figure II.2 TALSPEAK process
HCOOH
HDEHP
TBP
HLLW
Denitration
Feed solution
U, Pu, Np, Am
Cm, Ln(III)
extraction
FP
solution
HCOOH
Formic acid
rinse
Glycolic acid
DTPA
Am, Cm
stripping
Am, Cm solution
Solid residue
Nitric acid
Ln
stripping
Ln solution
Oxalic acid
U, Pu, Np
stripping
U, Pu, Np solution
Discharged
solvent
To prevent the formation of extracted polymers of metallic species which are difficult to strip,
such as Ans and Lns for example, it is necessary to limit the concentration of the metallic species in the
solvent. Consequently, the solvent inventory required for these processes is rather high.
In DIDPA process (see Figure II.3) more than 99.95% recovery of all actinides was
demonstrated with a simulated HLLW and 99.99% recovery of Am and Cm with real HLLW [5].
Recent activities of JAERI’s study are devoted to the confirmation of the effectiveness of the four group
partitioning process (see Annex B) including DIDPA extraction with real HLLW and to the
fundamental study on its practical application.
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