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Figure II.6 DIAMEX process
Feed solution
(3-5 M HNO 3)
Diamide
solvent
Rinse
U, Pu, Am,
Cm, Ln(III)
extraction
FP solution
HNO 3 (0.1 M)
An(III) + Ln(III)
stripping
An + Ln solution
An/Ln
Separation
Complexant or
reductant
(to be defined)
U, Pu
stripping
U, Pu, solution
Solvent
treatment
Selective extraction of actinides
Tripyridyltriazine (TPTZ)
Tripyridyltriazine ligand (TPTZ) is a terdendate nitrogen-donor ligand which can selectively
extract An(III) from An+Ln mixtures when used in synergistic combination with an organic cation
exchanger. This system was first studied in the 80s by Vitorge [17]. Good separation factors were
obtained for An(III) vs Ln(III) using TPTZ+HDNNS (di-nonylnaphthalenesulfonic acid) or TPTZ +
alpha-bromocapric acid. Tests of the process using synthetic spiked solutions were successfully
conducted at Fontenay-aux-Roses Research Centre. Improvements to the process are underway in a
European research programme. One way to improve the system is to use the lipophilic alkyl derivative
of TPTZ developed jointly by the University of Reading (UK) and the CEA (France). Recently, Kolarik
et al. at the FZK (Germany) designed a very efficient family of molecules related to TPTZ able to
extract selectively An(III) over Ln(III) from aqueous nitric acid solution [18].
CYANEX 301
Zhu et al. in Tsinghua University (China) recently published extraordinary results for the
separation of An(III) over Ln(III) using CYANEX 301 extractant [19]. CYANEX 301 consists chiefly
of bis (2,4,4-trimethylpentyl) dithiophosphinic acid. The commercial product contains many impurities
some of which are detrimental to the extraction of metal ions, and especially to the separation of An(III)
over Ln(III). In the case of crude CYANEX 301, no An/Ln separation is observed unless the extractant
is saponified (i.e. neutralised with an alkali). In this case, very high An(III)/Ln(III) separation factors
can be obtained. After purification of CYANEX 301 by precipitation of its ammonium salt, there is no
need for saponification of the extractant to obtain tremendously high An(III)/Ln(III) separation factors,
up to 5 900. Nevertheless, one of the drawbacks in using CYANEX 301 for An/Ln separation is the
fact that the aqueous solution must be adjusted to a rather high pH of 3.5 to 4.
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