Chemistry Reference
In-Depth Information
concentrations, assuming the formation of 1:1:1:
n
metal:anion:calixar-ene:modifier,
along with the aggregation of the modifier, and the aggregation of the latter with the
calixarene.
4.3.17 P
r o C e S S
f of r
e
X t r a C t i of in
of f
C
e S i u m
4.3.17.1 Process for extraction of Cesium from Acidic High-Activity
Level Waste
In the previous studies, calixarenes were not directly usable in a liquid-liquid extrac-
tion process, because used in a diluent (nitro phenyl hexyl ether), the hydrodynamic
properties were incompatible with such a process. The system has been modified in
order to satisfy the following criteria: density, viscosity, kinetics, and absence of a
third phase.
102
Two systems based on crown-calixarenes, able to be used in liquid-liquid extrac-
tion process were chosen. Both systems use a modifier in the organic phase to avoid
the occurrence of a third phase in the TPH (diluent used at the reprocessing plant of
la Hague for the PUREX process) and ensure a sufficient cesium extraction.
System 1 is based on MC8 (0.065 M) but needs the addition of TBP (1.5 M) in the
organic phase and the introduction of oxalic acid in the liquid waste to prevent the
extraction of zirconium by TBP. It has been pointed out that the addition of oxalic
acid is necessary for the PALADIN process, previously implemented for the extrac-
tion of minor actinides. The addition of TBP which extracts several cations, leads to
a lesser selectivity of the solvent.
System 2 is based on 1,3-(2,4-di-ethyl-heptyloxy)-2,4-calix[4]arene-crown-6
(MC9) (0.1 M), more difficult to synthesize, but the monoamide (methyloctyl-1,2-
dimethylbutanamide) (1 M) used as a phase modifier does not alter the selectivity of
the organic phase.
4.3.17.2 Flowsheets, experiments Realized with simulated
and Actual Waste
After acquisition of experimental data, flowsheet calculations were carried out.
A theoretical recovery of cesium was fixed at 99.99%. Hydraulic tests and chemi-
cal transfer tests were first carried out with centrifugal contactors, then with pulsed
columns, first on simulated effluents and then on actual effluents.
In the tests carried out in centrifugal extractors, the extraction and recovery of
cesium higher than 99.99% were obtained on simulated effluents, with a very good
coherence between calculated flowsheets and experimental results.
102
Tests confirmed
the feasibility of the implementation of the “cesium process” in pulsed columns, the
latter representing the most adapted contactors for the industrial implementation to
overcome the drawback due to the presence of solid matter in waste to be treated.
For cesium extraction, “Couette” columns have been used. The operations in such
a contactor can be easily extrapolated to a pulsed column, and the quantity of imple-
mented solvent is less important. The hydrodynamic behavior is satisfactory for the
two calixarene systems studied in spite of a more “emulsion-prone” behavior with
system 2. The selectivity obtained compared to other elements is excellent.
