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waste because the material used for the adsorption can be used as the mother material for the Sr and Cs
solidification.
Cobalt dicarbollides were first synthesised and produced in Czechoslovakia for application to
caesium and strontium extraction [31]. From 600 kg of hexachloro derivative of dicarbollide,
synthesised by KATCHEM (Prague), diluted in nitrobenzene, the extraction of strontium and caesium
has been tested on a plant scale in the former USSR [32]. The use of highly toxic nitrobenzene is a
drawback for the use of dicarbollides, so in the framework of a project supported by the European
Commission, efforts were focused on the synthesis of dicarbollides soluble in diluents other than
nitrobenzene. Promising results were achieved with bis-ylene cosan (BISPHECOSAN) diluted in
nitrophenyl-alkyl-ether (NPHE or NPOE) or in solubilizers such as diethylpropanesulfonamide
(DEPSAM) or dibutylmethanesulfonamide (DIBUMESAM). The presence of two phenyl groups
enhances the caesium extraction from acidic media [33].
1.1.4.2 Separation of caesium
The separation of caesium at the CEA (Dozol et al. [34]) was first approached in connection
with a 137 Cs decontamination study on highly saline low- and medium-level effluents, rich in sodium
nitrate.
The problem accordingly demanded highly selective separation chemistry, capable of
differentiating between two alkaline cations, sodium and caesium, chemically very similar but
possessing very different ionic radii.
The basic idea was to use macrocycles of the calixarene type, functionalized by etheroxide
chains. Calixarenes are cyclic oligomers produced by the condensation of phenolic units on
formaldehyde (the name is derived from their shape which resembles a calyx). They only display weak
complexing properties, and must be functionalized, for example, by grafting one or two etheroxide
chains on either side of the macrocycle cavity.
These compounds, called calix-crowns, thus display pre-organised co-ordination sites, which
can be perfectly adjusted to the dimensions of the Cs + ion, giving them strong affinity, and, above all,
outstanding selectivity in terms of caesium/sodium separation. Separation factors in the range of 30 000
in favour of caesium have been obtained.
These calix-crowns were naturally selected in an attempt to separate the caesium contained in
a real high-level effluent. The results obtained were highly satisfactory, particularly in terms of
selectivity, because no other fission product, actinide or chemical element, except for rubidium, was
extracted in more than 1 to 2% [36].
1.1.4.3 Separation of strontium
The SREX (Strontium Extraction) process complemented the TRUEX process for the
strontium removal from acidic HA liquid waste. Horwitz chose among the dicyclohexano 18-C-6
derivatives the lipophilic di-t-butylcyclohexano 18-C-6 (0.2 M) diluted in octanol [36]. Tests carried out
on simulated waste show the selectivity of crown ether since only barium and technetium are
appreciably extracted with strontium by the crown ether. Subsequently Horwitz proposed as diluent a
variety of phase modifier/paraffinic hydrocarbon mixtures, among them TBP (1.2 M) in Isopar L [37].
In Bhabha Atomic Research Centre (India), Kumar optimised the extraction of strontium by diluting
dicyclohexano 18-C-6 in a mixture butanol (80%)-octanol (20%) [38].
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