Ion Selective Resins: Development and Applications for Nuclear Waste Management
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of the radionuclide, and alter their behavior. Additionally, organic resins are completely combustible and can be used to reduce the volume of radioactive waste. Ion exchange resins containing phenolic groups are known to possess exceptionally high affinity to Cs and Sr in aqueous radioactive waste [8-11]. The ion selectivity of these resins is expected to be applicable to specific element separations. To test this hypothesis, initial experiments are performed with Eu3+ and La3+. The trivalent lanthanides are suitable homologues for the trivalent actinides Am3 + and Cm3 +. Introduction of 8-hydroxyquinoline in the molecular matrix is shown to induce an intragroup separation of La and Eu. The resins synthesized and examined in this work are given in Table I. Table I. Resins Examined
Resin
Symbol
Phenol Formaldehyde
PF
Catechol Formaldehyde Resorcinol Formaldehyde Phenol 8-Hydroxyquinoline Formaldehyde Catechol 8-Hydroxyquinoline Formaldehyde Resorcinol 8-Hydroxyguinoline Formaldehyde
CF RF PQF CQF RQF
GENERAL SYNTHESIS Materials and Analysis
Phenol, resorcinol, catechol, 8-hydroxyquinoline and formaldehyde (37% aqueous solution) were obtained from Aldrich and used without further purification. Europium nitrate from Aldrich was used. The lanthanum salt used was lanthanum chloride heptahydrate from Fluka. FTIR spectra were recorded on a 1600 Perkin-Elmer spectrophotometer using KBr pellets in the range 4000-400 cm-L. The moisture regain is determined by heating 0.1 g of resin in an air oven at I00°C for 24 hours, the loss of weight giving the percentage of water in the resin. For determination of total ion-exchange capacity, 0.25 g of resin in the H+ form of known moisture regain was equilibrated overnight with 50mL of 0.IN NaOH solution containing 5% NaCl. The amount of NaOH consumed in the exchange was determined by titrating the remaining NaOH in the supernatant with 0.IN HC1 solution.
The five resins were synthesized with phenol [a], catechol [b], resorcinol [c] and 8hydroxyquinoline [d] (Figure 1). Alkaline polycondensation of formaldehyde with phenolic compound gives an infusible, insoluble, amorphous, crosslinked polymer. By assuming the complete crosslinking, the repeating unit in such a polymer is given by the following expression
[8]. (C6H3- )(OH),, (CH2), where n = I for phenol and n = 2 for catechol and resorcinol. If all the -OH
groups are
accessible in the polymer, the theoretically expected H+->Na+ ion-exchange capacity in alkaline solution would be 8.9 meq/g for phenol and 15.6 meq/g for the two dihydroxybenzene resins. The measured values are in Table II.
1278
OH
OH
OH OH
OH
6 &
N c d Figure 1. Phenol [a], catechol [b], resorcinol [ejand 8-hydroxyquinoline [d] molecules. a
OH
b
Table II. Moisture regain and ion-exchange capacities for phenolic resins Ion-Exchange Capacity Moisture Regain Resin (% wt/wt) (meq/g(dry)) CF RF PQF CQF RQF
8.6 11.5 5.9 9.6 9.9
20 40 10 20 19
The ion exchange capacities for the catechol and resorcinol formaldehyde resins are lower than the theoretic
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