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  • Author: T. G. Srinivasan x
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Summary

Room temperature molten salts for possible application of recovery of fission palladium from irradiated nuclear fuel/wastes have been investigated. The redox behavior of a solution of palladium(II) chloride and 1-butyl-3-methylimidazolium chloride (bmimCl) at glassy carbon working electrode has been studied at various temperatures using cyclic voltammetry. The voltammogram of bmimCl-PdCl2 consists of a single reduction and two oxidation waves indicating that Pd2+ undergoes a single step two-electron quasi-reversible reduction process at the working electrode. Controlled potential deposition of palladium on platinum electrode gave a black deposit, which was characterized to be metallic palladium. Extraction of palladium by Aliquat-336 has been studied as a function of nitric acid concentration and the redox behavior of palladium in Aliquat-336 phase has been investigated by cyclic voltammetry. The results suggest that some aqueous insoluble room temperature ionic liquids can act both as extractant and electrolytic medium and also have the potential of recovering of palladium from nuclear wastes.

Summary

Third phase formation in the extraction of Th(IV) by tri-2-methyl butyl phosphate (T2MBP) in various diluents such as n-dodecane, n-tetradecane and n-hexadecane from nitric acid media has been investigated for the first time. The limiting organic concentration (LOC) and maximum organic concentration (MOC) as well as critical aqueous concentration (CAC) and saturated aqueous concentration (SAC) were measured as a function of equilibrium aqueous acidity. Data on LOC and MOC values have been generated with various concentrations of T2MBP (1.1 M, 1.38 M and 1.65 M) in n-dodecane at 303 K. LOC and CAC values have been measured for the extraction of Th(IV) by 1.1 M T2MBP/n-hexadecane at various temperatures (298 K, 303 K and 313 K) as a function of equilibrium aqueous acidity. Effect of temperature on third phase formation has been studied in the extraction of Th(IV) from its solution with near zero free acidity by 1.1 M T2MBP in n-tetradecane and n-hexadecane as diluents. Data on extraction of nitric acid in the absence and presence of Th(IV) by T2MBP/n-dodecane is also reported in this paper.

Summary

A new class of polymeric resin called MCM-BEHSA, for extraction of U(VI), Th(IV) and La(III) was synthesized by grafting Merrifield chloromethylated polymer with N,N-bis-(2-ethyl-hexyl)-succinamic acid. The chemical modifications at each step of the grafting was confirmed by FT-IR spectroscopy, CPMAS solid state NMR spectroscopy, CHN elemental analysis and also by Thermo Gravimetric analysis. All the parameters influencing the quantitative metal ion extraction were optimized by both static and dynamic methods. The resin showed good extractability over a wide range of acidity (0.01-10 M) with fast exchange rate (saturation possible within 20 minutes) and high sorption capacities for U(VI), Th(IV) and La(III). Quantitative metal desorption was achieved by using 0.5 M (NH4)2CO3 for all the analytes. A significant feature of this grafted polymer was its ability to extract Th(IV) from very high nitric acid concentrations. Interference studies with commonly encountered metal ions, rare earth ions and electrolytes showed very high tolerance limit for those ions. Enrichment factor values of 400, 550 and 350 with limit of quantification (LOQ) as 10 ng ml-1, 10 ng ml-1 and 20 ng ml-1 were observed for U(VI), Th(IV) and La(III), respectively. All the analytical data were within 3.2% rsd, reflecting the reproducibility and reliability of the developed method.

Summary

Alkali metal uranyl chloride (M2UO2Cl4 (M = Na or Cs)) was dissolved in 1-butyl-3-methylimidazolium chloride (bmimCl) and the redox behavior of uranyl ion present in the resultant solution was investigated by cyclic voltammetry at 343 K. The cyclic voltammogram consisted of a reduction wave occurring at the peak potential of −0.85 V, due to the reduction of U(VI) and two oxidation waves occurring at the peak potentials of −0.6 V and +0.2 V. Controlled potential electrolysis of uranium(VI) loaded bmimCl gave a black deposit, which was characterized as uranium oxide by EDXRF and XRD analysis. Extraction of uranium(VI) from nitric acid medium by 0.05 M tri-n-octylmethylammonium chloride (TOMAC) in chloroform was studied and the cyclic voltammogram of uranyl ion present in the extracted phase exhibited a single reduction (−0.8 V) and an oxidation wave (0.06 V) at 298 K. Controlled potential electrolysis of uranium(VI) loaded TOMAC at −1.0 V also gave a black uranium oxide deposit similar to that observed in the previous case. The results indicated that uranyl ion in organic phase undergoes a single step two electron quasi-reversible reduction at the working electrode, which can be conveniently exploited for the direct recovery of uranium from the spent fuel or from high level liquid wastes.

The extraction of plutonium from tissue paper matrix was carried out using supercritical carbon dioxide (Sc-CO2). The removal of plutonium was also studied from other matrices such as teflon, glass and stainless steel. Initial experiments were carried out under subcritical conditions. Supercritical extraction conditions were also employed in some experiments for the recovery of plutonium from tissue paper matrix. Complete extraction of Pu(III) as well as Pu(IV) in their nitrate form from tissue paper was achieved for the first time using supercritical carbon dioxide modified with n-octyl(phenyl)-N,N-diisobutyl carbamoylmethyl phosphine oxide (φCMPO) in methanol. Pu(IV) was also completely removed from other matrices such as teflon, stainless steel and glass. Studies on the extraction of Am(III) using supercritical carbon dioxide modified with CMPO in methanol resulted in its complete recovery from tissue paper.

In the above mentioned paper we had reported a non-linear dependence of limiting organic concentration (LOC) with temperature in the case of tri-2-methyl butyl phosphate in n-tetradecane as well as n-hexadecane diluents. Subsequently we extended the studies to other trialkyl phosphates such as TBP, TiBP, TsBP, TAP, TiAP and TsAP in various diluents (n-decane, n-dodecane, n-tetradecane, n-hexadecane and n-octadecane) and found recently that the dependence was always linear, irrespective of the extractant-diluent combination. This behaviour urged us to have a thorough review of the data reported earlier and when we repeated the studies again in the same systems, we found that the dependence was only linear and not as reported earlier.

We have critically looked into what went wrong in the earlier studies and at present have concluded that wrong temperature calibration/measurement might have induced the same.

We now present the correct data in Tables 1 and 2 and 4. Some parts of the sections “Results and discussion” and “Conclusions” are also modified.