Radioisotopic tracer technique for characterization of nuclear and non-nuclear grade ion exchange resins Tulsion A-23 and Indion-810

In the present paper 82 Br radioactive tracer isotopes was used for characterization of nuclear and non-nuclear grade ion exchange resins Tulsion A-23 and Indion-810 respectively. The bromide ion-isotopic exchange reactions were performed by equilibrating 1.000 g of conditioned resins in bromide form with labeled bromide ion solution of different concentrations ranging from 0.001 M to 0.004 M, in the temperature range of 30.0 °C to 45.0 °C. The resins were characterized by comparing the values of specific reaction rate (min -1 ), amount of bromide ion exchanged (mmol) and percentage of bromide ions exchanged under identical experimental conditions. It was observed that the above values decrease with rise in temperature and increases with increase in concentration of labeled bromide ion solution. From the experimental values of specific reaction rate, amount and percentage of bromide ions exchanged, it was observed that Tulsion A-23 resins are superior to Indion-810 resins under identical experimental conditions.


INTRODUCTION
Organic ion exchangers have proved to be reliable and effective for the control of both the chemistry and radiochemistry of water coolant systems at nuclear power plants and also for processing some liquid radioactive waste [1,2]. Nuclear power plant process water systems have typically used organic ion exchange resins to control system chemistry, to minimize corrosion or the degradation of system components and to remove radioactive contaminants. Efforts to develop new organic ion exchange resins for specific applications are continuing [3][4][5][6][7][8][9]. In spite of their advanced stage of development, various aspects of ion exchange technologies have been continuously studied to improve the efficiency and economy of their application in various industrial applications [10][11][12][13][14]. In order to select the ion exchange resins for any technological application, it is essential to have adequate knowledge about their performance under different operational conditions and also regarding their physical/chemical properties, which forms the complementary part of resin characterization study. Therefore in the present investigation, attempt is made to apply the radioisotopic tracer technique for characterization of nuclear and non-nuclear grade ion exchange resins Tulsion A-23 and Indion-810.

1. Conditioning of ion exchange resins
Ion exchange resin Tulsion A-23 (Nuclear grade resins by Thermax India Ltd., Pune), and Indion-810 (Non-nuclear grade resins by Ion Exchange India Ltd., Mumbai) are strongly basic anion exchange resin in hydroxide form. These resins were converted in to bromide form by treatment with 10 % KBr solution in a conditioning column. The resins were then washed with double distilled water, and then air dried at room temperature. The radioactive tracer isotope 82 Br used in the present study is an aqueous solution of ammonium bromide in dilute ammonium hydroxide having t 1/2 36 h, radioactivity 5mCi and γ-energy 0.36 MeV [15].

Study on kinetics of bromide ion-isotopic exchange reaction.
In a stoppered bottle 250 mL of 0.001 M bromide ion solution was labeled with diluted 82 Br radioactive solution using a micro syringe, such that 1.0 mL of labeled solution has a radioactivity of around 15,000 cpm (counts per minute) when measured with γ-ray spectrometer having NaI (Tl) scintillation detector. Since only about 50-100 μL of the radioactive bromide ion solution was required for labeling the solution, its concentration will remain unchanged, which was further confirmed by potentiometer titration against AgNO 3 solution. The above labeled solution of known initial activity was kept in a thermostat adjusted to 30.0 °C. The swelled and conditioned dry ion exchange resins in bromide form weighing exactly 1.000 g were transferred quickly into this labeled solution which was vigorously stirred by using mechanical stirrer and the activity in cpm of 1.0 mL of solution was measured. The solution was transferred back to the same bottle containing labeled solution after measuring activity. The bromide ion-isotopic exchange reaction can be represented as: R-Br + Br*ˉ( aq.) ↔ R-Br* + Brˉ( aq.) (1) Here R-Br represents ion exchange resin in bromide form; Br*ˉ( aq.) represents aqueous bromide ion solution labeled with 82 Br radiotracer isotope.
The activity of solution was measured at a fixed interval of every 2.0 min. The final activity of the solution was also measured after 3hours which was sufficient time to attain the equilibrium [16][17][18]. Similar experiments were carried out by equilibrating separately 1.000 g of ion exchange resin in bromide form with labeled bromide ion solution of four different concentrations ranging up to 0.004 M at a constant temperature of 30.0 °C. The same experimental sets were repeated for higher temperatures up to 45.0 °C.

RESULTS AND DISCUSSION
In the present investigation it was observed that due to the rapid bromide ion-isotopic exchange reaction taking place, the activity of solution decreases rapidly initially, then due to the slow exchange the activity of the solution decreases slowly and finally remains nearly constant giving rise to a composite curve (Figure 1). The specific reaction rate for the rapid exchange reaction was obtained by resolving the composite curve in the similar way as that explained in our previous work [16][17][18]. The amount of bromide ions exchanged (mmol) on the resin were obtained from the initial / final activity of solution and the amount of exchangeable bromide ions in 250 mL of solution.

ILCPA Volume 11
From the results it appears that the calculated values of specific reaction rate (min -1 ), amount of bromide ion exchanged (mmol) and percentage of bromide ion exchanged decreases with rise in temperature from 30.0 °C to 45.0 °C, using 1.000 g of resins in bromide form and 0.001 M labelled bromide ion solution (Table 1). It was observed that using Tulsion A-23 resin, at 30.0 °C; the above values were obtained as 0.175 min -1 , 0.128 mmol and 51.3 %; which at 45.0 °C decreases to 0.155 min -1 , 0.121 mmol and 48.5 % respectively. Similarly by using Indion-810 resin, the values calculated were 0.078 min -1 , 0.065 mmol and 25.8 % at 30.0 °C; which decreases to 0.065 min -1 , 0.055 mmol and 21.9 % at 45.0 °C ( Table 1) Table 2).
The overall result suggest that the calculated values of specific reaction rate (min -1 ), amount of bromide ion exchanged (mmol) and percentage of bromide ion exchanged were higher for Tulsion A-23 resin as compared to that obtained for Indion-810 resin under identical experimental conditions.