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Radio analytical technique in characterization of nuclear grade ion exchangers Duolite ARA-9366B and Purolite NRW-5010
Journal of Analytical Science and Technology volume 5, Article number: 30 (2014)
Ion exchange is one of the widely used techniques in nuclear industries for treatment of liquid radioactive waste. Regular efforts are being made in order to develop new ion exchange resins and their subsequent characterization so as to bring about efficient industrial performance. Among the different characterization techniques, radioactive tracer technique is one of the sensitive analytical techniques, mainly because of its non-destructive nature, high detection sensitivity, capability of in-situ detection, and physico-chemical compatibility with the material under study. The present work was therefore performed to demonstrate the application of the radioactive tracer technique in performance evaluation of two closely related nuclear grade anion exchange resins Duolite ARA-9366B and Purolite NRW-5010.
The short-lived radioisotope 131I and 82Br were used in the present experimental work to trace the kinetics of iodide and bromide ion-isotopic exchange reactions. The radioactivity was measured at various time intervals using γ-ray spectrometer having well type NaI(Tl) scintillation detector of Nucleonix make. From the radioactivity measured at various time intervals, the values of specific reaction rate (min−1), amount of ion exchanged (mmol), and initial rate of ion exchange (mmol/min) were calculated.
It was observed that for iodide ion-isotopic exchange reaction under identical experimental conditions of 30.0°C, 1.000 g of ion exchange resins and 0.001 mol/L labeled iodide ion solution, the above values were calculated as 0.246, 0.155, and 0.038, respectively for Purolite NRW-5010 resin, which was higher than the respective values of 0.201, 0.139, and 0.028 obtained for Duolite ARA-9366B resins. The identical trend was observed for the two resins during bromide ion-isotopic exchange reaction.
The overall results indicate that under identical experimental conditions, Purolite NRW-5010 resins exhibit superior performance over Duolite ARA-9366B resins. The same technique can be extended further for performance evaluation of different nuclear as well as non-nuclear grade ion exchange resins.
There are a number of liquid processes and waste streams at nuclear facilities (i.e., nuclear power plants, fuel reprocessing plants, nuclear research centers, etc.) that require treatment for process chemistry control reasons and/or the removal of radioactive contaminants (IAEA ). The treatment processes may be required for reactor primary coolants, the cleanup of spent fuel pools, liquid radioactive waste management systems, etc. One of the most common treatment methods for such aqueous streams is the ion exchange, which is a well-developed technique that has been employed for many years in both the nuclear industry and in other industries. In spite of its advanced stage of development, various aspects of ion exchange technology are being studied in many countries to improve its efficiency and economy in its application to radioactive waste management. Organic ion exchange resins have been developed over a much longer period of time than the selective inorganic ion exchangers that have recently become available in commercial quantities and can now meet the demands of the nuclear industry. The organic ion exchange resins are very effective at transferring the radioactive content of a large volume of liquid into a small volume of solid and 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 (Samanta et al. ; Samanta et al. ; Samanta et al. ; Kulkarni et al. ; Bray et al. ). In a number of cases, for specific physical and chemical reasons, organic resins cannot be replaced by commercially available inorganic ion exchangers. Also, organic ion exchange resins are used globally (Tomoi et al. ; Zhu et al. ; Kumaresan et al. ). The selection of an appropriate ion exchange material for treatment of liquid waste is possible on the basis of information provided by the manufacturer. However, since the selection of the appropriate ion-exchange material depends on the needs of the system, it is expected that the data obtained from the actual experimental trials will prove to be more helpful in the characterization and subsequent selection of the resins.
Although there are many alternative methods available for characterization of ion exchange resins (de Villiers et al. ; Harland ; Zeng et al. ; Patel et al. ; Liu et al. ; Masram et al. ), radioactive tracer isotopic technique is one of the sensitive analytical techniques (Sood et al. ; IAEA ). By monitoring the radioactivity continuously, the migration of the tracer and in turn, of the bulk matter under investigation, can be followed. As a result, radioisotopes have become a useful tool and almost every branch of industry, which uses them (Sood et al. ; IAEA ), and every radiotracer methodology, is described extensively in the literature (Clark et al. ; Dagadu et al. ; Koron et al. ). Considering the extensive technological application of radioactive tracers, in the present investigation, attempts are made to apply the same technique to study the kinetics of ion-isotopic exchange reactions in nuclear grade anion exchange resins Duolite ARA-9366B and Purolite NRW-5010. It is expected that the kinetics data obtained here will not only be used in characterization of these resins but also in standardization of the process parameters for their efficient application.
Conditioning of ion exchange resins
Duolite ARA-9366B (by Auchtel Products Ltd., Mumbai, India) and Purolite NRW-5010 (by Purolite International India Private Limited, Pune, India) are type I strong base, quaternary ammonium, nuclear grade anion exchange resins in hydroxide form. Details regarding the properties of the resins used are given in Table 1. These resins were converted separately in to iodide/bromide form by treatment with 10% (w/v) KI/KBr solution in a conditioning column which is adjusted at the flow rate as 1 mL/min. The resins were then washed with double distilled water, until the washings were free from iodide/bromide ions as tested by AgNO3 solution. These resins in bromide and iodide form were then dried separately over P2O5 in desiccators at room temperature.
Radioactive tracer isotopes
The radioisotope 131I and 82Br used in the present experimental work was obtained from Board of Radiation and Isotope Technology (BRIT), Mumbai, India. Details regarding the isotopes used in the present experimental work are given in Table 2.
Study on kinetics of iodide ion-isotopic exchange reaction
In a stoppered bottle 250 mL (V) of 0.001 mol/L iodide ion solution was labeled with diluted 131I radioactive solution using a micro syringe, such that 1.0 mL of labeled solution has a radioactivity of around 15,000 counts per minute (cpm) when measured with γ-ray spectrometer having NaI(Tl) scintillation detector. The γ-ray spectrometer used was Type GR 612 supplied by Nucleonix Systems Pvt. Ltd., India, having a well-type scintillation detector of Nucleonix make. Since only about 50 to 100 μL of the radioactive iodide ion solution was required for labeling the solution, its concentration will remain unchanged, which was further confirmed by potentiometer titration against AgNO3 solution. The above-labeled solution of known initial activity (A i ) was kept in a thermostat adjusted to 30.0°C. The swelled and conditioned dry ion exchange resins in iodide form weighing exactly 1.000 g (m) were transferred quickly into this labeled solution which was vigorously stirred by using a mechanical stirrer and the activity in counts per minute of 1.0 mL of solution was measured. The solution was transferred back to the same bottle containing labeled solution after measuring activity. The iodide ion-isotopic exchange reaction can be represented as:
Here, R-I represents ion exchange resin in iodide form; I*−(aq.) represents aqueous iodide ion solution labeled with 131I radiotracer isotope.
The activity of solution was measured at a fixed interval of every 2.0 min. The final activity (A f ) of the solution was also measured after 3 h which was sufficient time to attain the equilibrium (Singare et al. ; Lokhande et al. ; Lokhande et al. [2008a]; Lokhande and Singare ; Lokhande et al. ). The activity measured at various time intervals was corrected for background counts.
Similar experiments were carried out by equilibrating separately 1.000 g of ion exchange resin in iodide form with labeled iodide ion solution of four different concentrations ranging up to 0.004 mol/L at a constant temperature of 30.0°C. The same experimental sets were repeated for higher temperatures up to 45.0°C.
Study on kinetics of bromide ion-isotopic exchange reaction
The experiment was also performed to study the kinetics of bromide ion-isotopic exchange reaction by equilibrating 1.000 g of ion exchange resin in bromide form with labeled bromide ion solution in the same concentration and temperature range as above. The labeling of bromide ion solution was done by using 82Br as a radioactive tracer isotope for which the same procedure as explained above was followed. The bromide ion-isotopic exchange reaction can be represented as:
Here, R − Br represents ion exchange resin in bromide form; Br*−(aq.) represents aqueous bromide ion solution labeled with 82Br radiotracer isotope.
Results and discussion
Comparative study of ion-isotopic exchange reactions
In the present investigation, it was observed that due to the rapid 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. Preliminary studies show that the above exchange reactions are of first order (Singare and Lokhande ; Lokhande and Singare [2007, 2008]; Lokhande et al. [2006, 2008a]). Therefore, logarithm of activity when plotted against time gives a composite curve in which the activity initially decreases sharply and thereafter very slowly giving nearly straight line (Figure 1). Thus, it is evident that rapid and slow ion-isotopic exchange reactions are occurring simultaneously (Singare and Lokhande ; Lokhande and Singare [2007, 2008]; Lokhande et al. [2006, 2008a]). For both the ion-isotopic exchange reactions, using the two resins, the ion exchange process is film diffusion controlled during an initial short period and the tendency toward particle diffusion control increases as exchange continues (Lokhande et al. [2008b]). Presumably, the rapid exchange process taking place during the initial short period was film diffusion controlled; while the slow exchange process near the end was particle diffusion controlled. The specific reaction rate for the rapid process was obtained by resolving the composite curve as is done to determine the decay constants of radioactive isotopes in a mixture. The rapid process is completed in a short time, but the slow process continues for a much longer time. At the late stage, the slow exchange is the only reaction that takes place, and the logarithm of activity (cpm) curve against time is a straight line. Now, the straight line was extrapolated back to zero time. The extrapolated portion represents the contribution of slow process to the total activity which now includes rapid process also. The activity, due to slow process, was subtracted from the total activity at various time intervals. The difference gives the activity due to the rapid process only. From the activity exchanged due to rapid process at various time intervals, the specific reaction rates (k) of rapid ion-isotopic exchange reaction were calculated. The amount of iodide/bromide ions exchanged (mmol) on the resin were obtained from the initial and final activities of solution and the amount of exchangeable ions in 250 mL of solution. From the amount of ions exchanged on the resin (mmol) and the specific reaction rates (min−1), the initial rate of ion exchanged (mmol/min) was calculated.
Because of the larger solvated size of bromide ions as compared to that of iodide ions, it was observed that the exchange of bromide ions occurs at the slower rate than that of iodide ions. Hence, under identical experimental conditions, the values of specific reaction rate (min−1), amount of ion exchanged (mmol) and initial rate of ion exchange (mmol/min) are calculated to be lower for bromide ion-isotopic exchange reaction than that for iodide ion-isotopic exchange reaction as summarized in Tables 3 and 4. For both bromide and iodide ion-isotopic exchange reactions, the value of specific reaction rate increases with increase in the concentration of iodide and bromide ions in solution from 0.001 mol/L to 0.004 mol/L (Table 3). However, with rise in temperature from 30.0°C to 45.0°C, the specific reaction rate was observed to decrease (Table 4). Thus, in case of Purolite NRW-5010 at 30.0°C, when the concentration of iodide and bromide ions in solution increases from 0.001 mol/L to 0.004 mol/L, the specific reaction rate value for iodide ion-isotopic exchange increases from 0.246 to 0.290 min−1, while for bromide ion-isotopic exchange, the value increases from 0.203 to 0.245 min−1. Similarly, in the case of Duolite ARA-9366B, the value for iodide ion-isotopic exchange increases from 0.201 to 0.235 min−1, while for bromide ion-isotopic exchange the value increases from 0.165 to 0.186 min−1. However, when the concentration of iodide and bromide ions in solution is kept constant at 0.001 mol/L and temperature is raised from 30.0°C to 45.0°C; in the case of Purolite NRW-5010, the specific reaction rate value for iodide ion-isotopic exchange decreases from 0.246 to 0.219 min−1, while for bromide ion-isotopic exchange, the value decreases from 0.203 to 0.178 min−1. Similarly, in case of Duolite ARA-9366B, the specific reaction rate value for iodide ion-isotopic exchange decreases from 0.201 to 0.156 min−1, while for bromide ion-isotopic exchange, the value decreases from 0.165 to 0.125 min−1. From the results, it appears that iodide ion exchange has the faster rate as compared to that of bromide ions which was related to the extent of solvation (Tables 3 and 4).
Comparative study of anion exchange resins
From the Tables 3 and 4, it is observed that for iodide ion-isotopic exchange reaction using Purolite NRW-5010 resin, the values of specific reaction rate (min−1), amount of iodide ion exchanged (mmol), and initial rates of iodide ion exchange (mmol/min) were 0.246, 0.155, and 0.038, respectively, which were higher than 0.201, 0.139, and 0.028, respectively, as that obtained using Duolite ARA-9366B resins under identical experimental conditions of 30.0°C, 1.000 g of ion exchange resins, and 0.001 mol/L labeled iodide ion solution. The identical trend was observed for the two resins during bromide ion-isotopic exchange reaction.
From Table 3, it is observed that using Purolite NRW-5010 resins at a constant temperature of 30.0°C, as the concentration of labeled iodide ion solution, increases from 0.001 to 0.004 mol/L, the percentage of iodide ions exchanged also increases from 61.80% to 68.90% while using Duolite ARA-9366B resins, under identical experimental conditions, the percentage of iodide ions exchanged increases from 55.40% to 62.90%. Similarly, in the case of bromide ion-isotopic exchange reaction, the percentage of bromide ions exchanged increases from 52.20% to 55.70% using Purolite NRW-5010 resin, while for Duolite ARA-9366B resin, it increases from 48.30% to 52.80%. The effect of ionic concentration on the percentage of ions exchanged is graphically represented in Figure 2.
From Table 4, it is observed that using Purolite NRW-5010 resins, for 0.001 mol/L labeled iodide ion solution, as the temperature increases from 30.0°C to 45.0°C, the percentage of iodide ions exchanged decreases from 61.80% to 59.80% while using Duolite ARA-9366B resins, the percentage of iodide ions exchanged decreases from 55.40% to 50.10%. Similarly, in case of bromide ion-isotopic exchange reaction, the percentage of bromide ions exchanged decreases from 52.20% to 45.40% using Purolite NRW-5010 resin, while for Duolite ARA-9366B resin, it decreases from 48.30% to 40.60%. The effect of temperature on percentage of ions exchanged is graphically represented in Figure 3.
The overall results indicate that under identical experimental conditions, as compared to Duolite ARA-9366B resins, Purolite NRW-5010 resins shows higher percentage of ions exchanged. Thus, Purolite NRW-5010 resins show superior performance over Duolite ARA-9366B resins under identical operational parameters.
The results of the present investigation show a strong negative correlation between the amount of ions exchanged and temperature of exchanging medium (Figures 4 and 5). In the case of iodide ion-isotopic exchange reactions, the values of r calculated for Purolite NRW-5010 and Duolite ARA-9366B resins were −0.9487 and −0.9944, respectively. Similarly, in the case of bromide ion-isotopic exchange reactions, the r values calculated were −0.9994 and −0.9899, respectively, for both the resins.
Extensive work reported in the literature on synthesis of new ion exchange materials and their characterization itself is an indication that these resins are the wave of the present research and the material of new generation. Although there are a number of techniques reported in the literature on characterization of ion exchange resins, the radioisotopic tracer technique has emerged as one of the effective non-destructive analytical techniques. The present research paper therefore is a successful demonstration on the application of radiotracer isotopes in the characterization of nuclear grade ion exchange resins Duolite ARA-9366B and Purolite NRW-5010. The results of the present investigation may help to optimize the operational process parameters for efficient performance of these resins in various technical applications. The same technique can also be extended further for characterization of different non-nuclear grade ion exchange resins. It is anticipated that the results of such work will be useful in deciding about the selection of the resins in various industrial applications.
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Singare, P.U. Radio analytical technique in characterization of nuclear grade ion exchangers Duolite ARA-9366B and Purolite NRW-5010. J Anal Sci Technol 5, 30 (2014) doi:10.1186/s40543-014-0030-5
- Nuclear grade resins
- Duolite ARA-9366B
- Purolite NRW-5010
- Reaction kinetics
- Ion-isotopic exchange reactions