STRONG BASIC ANION EXCHANGERS WITH ADSORPTION PROPERTIES FOR CHLOROCOMPLEX URANYL ION

Ecaterina Stela Dragan1, Ecaterina Avram1, Damian Axente2, Cristina Marcu2

1“Petru Poni” Institute of Macromolecular Chemistry, 700487-Iasi, Romania		
2 National Institute for Research and Development of the Isotopic and Molecular Technologies, 400293 Cluj-Napoca, Romania

By their high chemical resistance, styrene-divinylbenzene copolymers (S-DVB) are still the most commonly used as starting copolymers in the synthesis of ion exchangers with special destinations, such as the enrichment process of 235U. For this purpose, a special concern has been lately focused on the preparation of macroporous strong basic anion exchangers containing one or two hydroxyalkyl substituents. An average pore radius around 1000 Å, which is correlated with a high permanent porosity, a good stability of the resin in HCl with concentrations up to 8 N, a thermal resistance up to 150 oC at least and a high mechanical strength are the main characteristics requested for this purpose. In a previous work we have reported the preparation of some macroporous S-DVB copolymers with sizes in the range 90-200 m by employing 2-ethyl-1-hexanol as a porogen, at a high dilution of monomers (D ≥ 0.55) and their subsequent transformation in macroporous strong basic anion exchangers with an average pore radius higher than 50 nm [1,2]. In the present study, the characteristics of the starting S-DVB macroporous copolymers synthesized in the presence of N-butilic alcohol (nBA) as porogen and those of the strong basic anion exchangers derived therefrom have been followed. Functionalization by chloromethylation reaction of the macroporous S-DVB copolymers was performed with paraformaldehyde (CH2O)n/trimethylchlorosilane (TMCS) in the presence of FeCl3 as catalyst, in chloroform as a reaction medium. Strong basic anion exchangers with diethyl 2-hydroxyethyl benzylammonium groups were obtained by the amination of the chloromethylated S-DVB copolymers with diethyl 2-hydroxyethylamine (DEHEA). The corresponding strong basic anion exchangers showed an ionic exchange capacity in the range 1.8-2.2 meq/g, depending on the crosslinking degree and the dilution of the starting copolymer, and an average pore radius, rp, around 80 nm. Such characteristics make these resins promising candidates for the adsorption of uranyl chlorocomplexes as it has been already demonstrated by the preliminary tests carried out comparative with some commercial anion exchange resins special synthesized for uranium isotope exchange [3]. 

References:
1. E. S. Dragan, E. Avram, D. Axente, C. Marcu, Ion exchange resins. III. Functionalization-Morphology Correlations in the Synthesis of Some Macroporous, Strong Basic Anion Exchangers and Uranium-Sorption Properties Evaluation, J. Polym. Sci. Part A Polym. Chem. Ed., 42, pp. 2451-2461 (2004).
2. S. Dragan, D. Csergö, I. Manolescu, A. Carpov, 2-Ethyl-1-Hexanol as Diluent in the Synthesis of Styrene-Divinylbenzene Copolymers and Anion Exchangers. I. Morphological Aspects, React. Polym., 5, pp. 123-131 (1987).
3. D. Axente, C. Marcu, E. S. Dragan, E. Avram, Adsorption of U(VI) from HCl solutions on anion exchange resins, Rev. Chim. in press