Chapter 26 Cesium Removal from Nuclear Waste Water by Supported Liquid Membranes Containing Calix-bis-crown Compounds 1
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1,3
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2,3
Z. Asfari , C. Bressot , J. Vicens , C. Hill , J.-F. Dozol , H. Rouquette , S. Eymard , V. Lamare , and B. Tournois 2
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Downloaded by AUBURN UNIV on April 18, 2017 | http://pubs.acs.org Publication Date: May 5, 1996 | doi: 10.1021/bk-1996-0642.ch026
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Ecole Européenne des Hautes Etudes des Industries Chimiques de Strasbourg, Unité de Recherche Associée 405 du Centre National de la Recherche Scientifique, 1 rue Blaise Pascal, F-67008 Strasbourg, France S.E.P./S.E.A.T.N., Centre d'Etudes de Cadarache, Commissariat à l'Energie Atomique, 13108 Saint-Paul-lez-Durance, France 2
Calix[4]-bis-crowns 1-7 are used as selective cesium-carriers in supported liquid membranes (SLMs). Application of the Danesi diffusional model allows the transport isotherms of trace level Cs through SLMs (containing calix[4]-bis-crowns) to be determined as a function of the ionic concentration of the aqueous feed solutions. Compound 5 appears to be much more efficient than mixtures of crown ethers and acidic exchangers, especially in very acidic media. Decontamination factors greater than 20 are obtained in the treatment of synthetic acidic radioactive wastes. Permeability coefficient measurements are conducted for repetitive transport experiments in order to determine the SMLs stability with time. Very good results (over 50 days of stability) and high decontamination yields are observed with 1,3-calix[4]-bis-crowns 5 and 6. 137
It is well known that 137-cesium is one of the most important radionucleotides present in the nuclear wastes and its removal can reduce storageriskscaused by its long halflife (2 χ 10 y) (/,2). It has been demonstrated that crown ethers are promising metal ion extractants and carriers in liquid membranes (3). A new family of crown ether-type compounds is now emerging: the calixcrowns. These molecules combine calixarene and crown ether elements in their molecular structure. Since Alfieri et al.(4) reported the synthesis of the first member of a new class of macropolycyclic crown compounds with the two opposite OH groups in />-ter/-butylcalix[4]arene bridged by a pentaethylene glycol chain, the 1,3-capping of calix[4]arenes at the lowerrimhas been achieved with poly(oxyethylene) chains leading to calixcrown ethers (5), doubly crowned calixes (5c, 6), and a double-calix-crown (7). Due to the presence of a glycol chain in their framework, calixcrowns have been used as complexing agents of alkali and alkaline-earth metal cations. The selectivities of complexation were shown to 6
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Corresponding author 0097-6156/96/0642-0376$15.00/0 © 1996 American Chemical Society
Bartsch and Way; Chemical Separations with Liquid Membranes ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
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ASFARI ET AL.
depend on the conformation (cone, partial cone, 1,2-alternate and 1,3-alternate) adopted by therigidifiedcalix[4]arene unit. For example the partial-cone isomer of 1,3dimethoxy-/?-/^r/-butylcalrx[4]crown-5 exhibited the highest free energy for complexation of potassium cation (5b) and was used as a selective carrier of this cation in supported liquid membranes (5c). The K selectivities of three different conformers of l,3-diethoxy-p-/e/*/-butylcalix[4]crown-5 have been measured for chemically modified field effect transistors (CHEMFETs) (5k) and membrane ion-selective electrodes (ISEs) (5d). The ionophores showed decreasing K /Na selectivities in the order: partial cone > 1,3-alternate > cone. The l,3-dialkoxycalix[4]crown-6 compounds in the l 3-alternate conformation exhibited binding preference for cesium ion (5e). The X-ray crystal structure of the 1:1 complex of 1,3dimethoxycalix[4]crown-6 with cesium picrate indicated the presence of cation/πelectron interactions (5e). In this contribution, we report the use of l,3-calix[4]-W.scrowns 1-7 (Chart I) as selective cesium-carriers in supported liquid membranes (SLMs). +
+
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Sodium-Cesium Extractions. Removal of cesiumfrommedium-level radioactive wastes involves extraction of cesium from aqueous solutions which are 1 M in HN0 and 4 M in NaN0 (8). In a preliminary study, extraction experiments with ligands 1-7 were performed by mixing equal volumes (5 to 7 mL) of aqueous and organic solutions (calixarene : ΙΟ· M in 2nitrophenyl hexyl ether or 2-NPHE) in sealed polypropylene tubes for one hour at room temperature (25 ± 1 °C). The aqueous solutions contained either NaN0 or CsN0 (5.0x10 M) in HN0 (1 M) to assess the selectivity toward cesium in the hypothetical presence of sodium. A measure for the selectivity was assumed to be the ratio of the distribution coefficients obtained separately for both cations : 3
3
2
3
3
3
D
«(«-., - ΐ
Y
\M]
*"· = 114
where : 2 [A/] denotes the total concentration of the metal cation (complexed and uncomplexed) in the organic phase at equilibrium, and ^ [M] denotes its total concentration in the aqueous phase at equilibrium. Σ [M] and 2 [M] were determined experimentally by analyzing aliquots (2 or 5 mL) of each phase by gamma spectrometry after centrifugation. From the data shown in Table I, it is seen that ligands 2, 5 and 6 with six oxygen atoms in the glycol chain are much more selective for cesium over sodium than 1 and 3 with five or seven oxygen atoms in theirrings,or 4 and 7, in which the polyether chains are sterically constrained by the presence of phenyl units. We have previously noted that the glycolic chains containing five oxygens in p-tert-butylcal\x[4]-bis-crovm-5, related to 1, are suitable for potassium and sodium cations, but are too small for the larger cesium (6e). In comparison, 2, 5 and 6 show 100-times higher selectivities toward cesium than do crown ethers w-decyl-benzo-21 -crown-7 (8), and ter/-butyl-benzo-21crown-7 (9), which are well known for their abilities to complex and extract large alkali cations from acidic media (8). One explanation is that the complexes with calixarene
Bartsch and Way; Chemical Separations with Liquid Membranes ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
CHEMICAL SEPARATIONS WITH LIQUID MEMBRANES
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l,3-caIix[4]-ô/5-crown-5 1 l,3-calk[4]-£/s-crown-6 2 l,3-calix[4]-i/$-crown-7 3 l,3-ca!ix[4]-o/.y-/?-benzo-crown-6 4
l,3-calix[4]-to-o-benzo-crown-6 5 l,3-calbc[4]-o«-naphthyl-crown-6 6 l,3-caUx[4]-6/.s-diphenyl-crown-6 7
Chart I : l,3-Calix[4]-ow-crowns 1-7.
Bartsch and Way; Chemical Separations with Liquid Membranes ACS Symposium Series; American Chemical Society: Washington, DC, 1996.
26.
ASFARI ET
Cesium RemovalfromNuclear Waste Water 379
Table I : Liquid-liquid Extraction Experiments : Selectivity Determination : +
Aqueous feed solution: M (N0 ): 5.0xl(H M in H N 0 : 1 M . Organic solution: Extracting agent: ΙΟ* M in 2-nitrophenyl hexyl ether. 3
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N° Extracting agents
Das
α
(θ/ΑΤα)
0.4
-
19.5
1500
1
1,3-Calk[4]-o/5-crown-5
2xl0*
2
1,3-Calix[4]-A/5-crown-6
1.3χ10·
3
1,3-Calix[4]-ow-crown-7
< ίο-
4
1,3-Calix[4]-to-/?-benzo-crown-6
