Study on the Temperature Effect on Regeneration of Iodide Form of Resin Into Multiatomic Anionic Forms

The pressurized heavy water reactors make use of heavy water in moderator and in primary heat transport system. The cationic fission products produced during the reactor operation such as Cesium, Strontium, Cobalt, Palladium, Ruthenium and anions Iodide, Iodate, Ruthenate etc. contaminate the heavy water. Columns containing Ion exchange resins in on line are used for purification. In this purification process, the resins pick up activity and ionic impurities. It is imperative to treat the spent resin into innocuous form. Hence an attempt has been made to convert the Iodide containing spent resin into multi atomic anionic forms viz. chlorate, dichromate, permanganate and oxalate forms and study the role of temperature in the exchange reactions. The exchange reactions were found to be endothermic with enthalpies 170.79 KJ/mole for chlorate, 161.59 KJ/mole for dichromate, 119.68 KJ/mole for Permanganate and 83.07 KJ/mole for Oxalate.


Introduction
Spent resins are generated in purification of primary heat transport system, moderator system, and spent fuel storage pond water.The spent resin containing cationic and anionic fission products is disposed in the radioactivity disposal area without treatment or fixed in cement or in thermosetting polymer as reported (Plecas et al., 2003).Direct immobilization in thermosetting resin, cement etc. results in final product whose volume is more than that of the original waste form.Incineration of spent resin involves burning at higher temperature (700 ºC) which entails problem of handling off gasses, corrosive fumes of NOX, SO 2 etc. and radioactivity from the resin.Also it does not result in complete burning and therefore results in tarry residue.
Acid digestion, the other alternate method, generates new kind of waste solutions and complicates the final disposal as reported (Miriam et al., 1982).Also it needs handling of concentrated mineral acids and handling off gasses viz.NOX, SO 2 etc. Wet oxidation did not completely oxidize organic carbon to carbon dioxide gas as reported (Kuobota et al., 1983).
Hence an attempt has been made to convert the spent resin into multi atomic anionic forms.Regeneration of spent resin into multi atomic anionic forms renders the handling of the almost non-active resin easy which can be fixed in cement or polymer safely.
Not much literature is available on the regeneration of spent resin into multi atomic anionic forms but there are literatures on the feasibility and conditions of conversion of one form of resin into another form (Vogel, 1978).
Since the regeneration of the spent resin can be efficiently carried out if we know the role of temperature on the regeneration, the experiments on the effect of temperature on the exchange of Iodide form of resin with multi atomic anions is relevant.
Results indicate that in the conversion of the Iodide form of the resin into multi atomic anionic forms, the equilibrium constant for the exchange reactions increases with temperature favoring the conversion at higher temperature.

Materials
OH -form of anion exchanger of make Indion 850, porous weak base was used for the experiment.The resin is a www.ccsen high poros which is g AR grade AR grade from M/s.

Estim
The excha 500 ml of indicator.The apparent equilibrium constant at various temperatures (K app ) were estimated from the strength of the unexchanged multi atomic ions in the solution phase, exchanged Iodide ion in the solution phase and the remaining Iodide and multi atomic ions in the resin phase obtained from the exchange capacity of the resin.Figures 3a-3d shows the plot of variation of log K app of the exchange reaction with multi atomic ion concentration.Also the enthalpy of the exchange reaction (H) was calculated using Gibbs Helmholtz equation based on the relation between the variation of K ther with temperature and the enthalpy of the reaction.Figure 4 shows the plot of log K ther against 1/T to obtain the enthalpy of exchange reactions between Iodide form of the ion exchanger with multi atomic anions.

Study of Mechanism of Exchange of Iodide Form of Resin With Multi Atomic Anions
From Figure 1, we find that the % regeneration of Iodide to vary between 0-5, 1.5-6.9,3-9.2, 5.1-12.8from 10 to 40 minutes before interruption using chlorate, dichromate, permanganate and Oxalate.After interruption for 20 minutes, the % regeneration was found to change from 5-9.5, 6.9-12, 9.2-15.4,12.8-20.4from 60 minutes to 90 minutes using chlorate, dichromate, permanganate and Oxalate.The slopes of the % regeneration vs timing before and after interruption are found to be 0.16 & 0.15 for chlorate, 0.18 & 0.17 for dichromate, 0.20 & 0.21 for permanganate and 0.256 & 0.253 for Oxalate which indicates the slope before and after the interruptions are almost the same giving credence to the film diffusion mechanism (Helfferich, 1962).

Extent of Regeneration
The exchange capacity of resin was found out to be 0.616 m.eq/g.
From Figures 2a-2d, we find that the percentage regeneration of Iodide form of the resin into multiatomic anionic forms increases with increase in the strength of the multi atomic ionic solution.Also the percentage regeneration was found to increase with temperature.As the strength of the multi atomic anionic increases from 6.16-30.80mN, the available multi atomic anions in 100 mL of the solution increases from 0.616 to 3.080 m.eq.As the exchange capacity was found to be 0.616 m.eq/g, the amount of multi atomic anions needed for 100% conversion of 1 g of the resin is 0.616 m.eq.Since the availability of multi atomic ions was more with its concentration, the percentage regeneration was found to increase with strength of the solution.
The coefficient of determination, R 2 gives the proportion of the variance (fluctuation) of one variable that is predictable from the other variable.Analysis of the coefficient of determination of the variation between the percentage regeneration with % stoichiometry of the exchanging ions at different temperatures shows that the data are more linear at higher temperatures as the coefficient of determination values are more than 0.8 at higher temperatures in all the cases.
The charge to radius ratios of the anions chlorate, dichromate, permanganate and oxalate are 0.00166, 0.001873, 0.001976, and 0.003778.The radius ratio for Iodide is 0.01053.The ionic potential, the charge to radius ratio of the ions follow the sequence Oxalate>Permanganate>dichromate>chlorate, We find that the exchange of Iodide form of resin with the multi atomic anions also follow the same sequence.

Effect of Temperature on Equilibrium Constant
More rigorous calculations were made by including the activity coefficients of the counter ions in the solution to compute the thermodynamic equilibrium constant (Lokande & Singare, 2001;Walton et al., 1961).The ion exchange reactions were utilized for the determination of activity coefficients in mixed electrolytes (Vanselow, 1932), thermodynamic calculation of cation exchange selectivities (Boyd, 1956) and equilibrium constants of cation exchange processes (Argersinger, 1952) and for estimation of enthalpy of exchange reactions of uni bivalent ions (Bonner & Pruett, 1959).
The ion exchange reaction at equilibrium may be represented as The apparent equilibrium constant was calculated using the equation: Where RI refers to the amount of I -in the resin phase and [I -] refers to the amount of Iodide concentration in the solution phase respectively.The f s represent the activity coefficients of the ions in the solution phase.
logK app was plotted against equilibrium concentration of multi atomic anions in the solution which was extrapolated to zero equilibrium concentration of multi atomic anions to get K th for the exchange reactions of Iodide form of the resin.The activity coefficient of the ions (f) in the solution phase was computed from the Debye Huckel limiting law logf = -A√µ Z 2 where µ is the ionic strength given by µ where Zi and c i are the charge and concentration of the ion and A is the Debye Huckel constant.

Effect of Temperature on the Equilibrium Constant in the Exchange of Iodide Loaded Resin With Multi Atomic Anions
Figure 3a, the plot of log K app vs equilibrium strength of chlorate ion at different temperatures for chlorate as regenerant for exchange with Iodide form of resin give rise to straight lines with equations y = 0.1462x-6.9701,y = 0.1048x-5.2065,y = 0.1034x-4.1561and y = 0.0518x-1.8873showing the thermodynamic equilibrium constants as 1.07×10 -7 , 6.215×10 -6 , 6.98×10 -5 and 1.30×10 -2 at 303, 323, 343 and 363 K.
From Figures 3a-3d, we observe that the equilibrium constant of the exchange reaction was observed to be more with temperature

Enthalpy of Ion Exchange Reactions
In order to get the enthalpy of the exchange reaction, use is made of the Gibbs Helmholtz relation between the variation of equilibrium constant with temperature and the enthalpy of the reaction given by dlnK/dT = H/RT 2 Which in the integrated form gives log K = -H/2.303RT+C The line equations in the plot of log K th Vs 1/T are y = -8916x+22.34,y = -8436x+21.36,y = -6248x+15.72,and y = -4337.7x+10.084for chlorate, dichromate, permanganate and Oxalate (Figure 4) respectively.Also the regression analysis shows that the coefficient of determination R 2 between 1/T against log (equilibrium constant) using chlorate, dichromate, permanganate and Oxalate are 0.9988, 0.9768, 0.9993 and 0.9819 respectively indicating that the equilibrium constant variation with temperature is linear.
From the slopes of the line (Figure 4) the exchange reactions were found to be endothermic with enthalpies 170.79 KJ /mole for chlorate, 161.59 KJ/mole for dichromate, 119.68 KJ/mole for Permanganate and 83.07 KJ/mole for Oxalate.

Conclusion
Ion exchange reactions between Iodide form of resin with multi atomic anions viz.chlorate, dichromate, permanganate and Oxalate etc. were carried out at various temperatures.The order of exchange of Iodide form of resin with multi atomic anions follows the sequence

Oxalate>permanganate>dichromate>chlorate
Results indicate that the reactions are endothermic, favoring the exchange reactions at higher temperatures.
the resin was plotted against strength of multi atomic ions in solution at various temperatures (Figures2a-2d).

Figure 2a .
Figure 2a.Regeneration of Iodide form of resin into chlorate form at different temperatures