R. C. Hubli

N,N,N ,N -tetra(2-ethylhexyl) thiodiglycolamide T(2EH)TDGA: A novel ligand for the extraction of palladium from high level liquid waste (HLLW)

Abstract A novel neutral multidentate ligand N, N, N′, N′-tetra(2-ethylhexyl) thiodiglycolamide T(2EH)TDGA was synthesized and examined for the extraction of palladium from nitric acid medium. Extraction equilibrium studies showed that almost complete extraction of palladium was obtained within 5 min. The influence of nitric acid, nitrate ion and T(2EH)TDGA concentration on the distribution of palladium has been investigated. With the increase in nitric acid/nitrate ion concentration, increase in extraction of palladium was observed. Stoichiometry of the extracted species was found to be Pd(NO3)2·2T(2EH)TDGA by slope analysis method. Loading studies with 10−3 M T(2EH)TDGA/n-dodecane show maximum uptake of 5.44×10−4 M palladium thus conforming to above stoichiometry of metal to ligand. Acid uptake studies have shown that 1:1 stoichiometry exists between T(2EH)TDGA and HNO3 at nitric acid concentration above 3.5 M. The effect of various diluents on the extraction of palladium was studied and it was found that there is quantitative uptake irrespective of the nature of diluents. More than 99% of palladium was back extracted in single contact using 0.01 M thiourea in 0.1 M nitric acid. Extraction studies with HLLW elements showed negligible uptake of U, Am, Eu, Sr, Cs and Ru.

Separation of palladium from high level liquid waste – A review

The present paper provides a review of the various processes/schemes developed for the separation and recovery of palladium from high level liquid waste (HLLW) generated during reprocessing of spent nuclear fuel. This separation is necessary in view of various problems posed by the presence of palladium during vitrification of HLLW. Further, to meet the ever increasing demand for palladium in various applications, HLLW can be considered as one of the possible secondary sources of this valuable metal. In this regard several processes are proposed involving liquid–liquid extraction, solid phase extraction, precipitation electro-deposition, for recovering palladium from HLLW. The focus of the present review is to evaluate various liquid–liquid extraction processes proposed for palladium separation from HLLW.

N,N,N′,N′-Tetra(2-Ethylhexyl) Thiodiglycolamide T(2EH)TDGA: A Promising Ligand for Separation and Recovery of Palladium from High Level Liquid Waste (HLLW) Solutions

The extraction properties of N,N,N′,N′-tetra(2-ethylhexyl)thiodiglycolamide T(2EH)TDGA have been evaluated for the separation and recovery of palladium from simulated high-level liquid waste (SHLW). T(2EH)TDGA has shown very high selectivity for Pd (II) over other metal ions present in SHLW. The separation factor (SF) for Pd (II) over other metal ions was found to be more than 105. Reusability studies of the extractant indicate that DPd remained almost constant even after five successive cycles of extraction and stripping. Palladium was quantitatively recovered from thiourea strip solution by treating it with ammonia and filtering the precipitate of palladium sulphide. The acid uptake constant (KH) was found to be 0.62 which could be due to the presence of two carbonyl groups of amidic moiety. To account for very high extractability of palladium with T(2EH)TDGA over other ‘S’ donor extractants, namely Bis-(2-ethylhexyl)sulphoxide (BESO), FTIR, as well as Raman studies were carried out. FTIR and Raman studies suggested the ligation through carbonyl as well as the thio-ether group. Conditional extraction constants (log K′ex) were determined and the thermodynamic parameters were calculated from the dependence of the conditional extraction constant (log K′ex) on temperature. The calculated values of ΔGex, ΔHex, and ΔSex were −41.78 kJmol−1, −55.12 kJmol−1 and −44.04 JK−1 mol−1 respectively. The extraction process is indicated to be enthalpy driven with the entropy factor counteracting it.

N,N,N-Trimethyl benzyl ammonium bis-(2-ethylhexyl)-phosphonate grafted polymer – a solid supported ionic liquid for the separation of uranium from aqueous processing streams

A new solid supported ionic liquid (SSIL) has been synthesized and evaluated for the separation of uranium from acidic aqueous streams. SSIL has provided an opportunity to exploit the anchored task specific ionic liquid (TSIL) moiety for the sorption of uranium from aqueous streams and thus overcoming the limitations encountered during liquid–liquid extraction processes involving the use of TSILs.

Studies on hydrolytic and radiolytic stability ofN,N,N´,N´-tetra-(2-ethylhexyl) thiodiglycolamide T(2EH)TDGA

Abstract Hydrolytic and radiolytic stability of T(2EH)TDGA solvent system has been investigated to establish its application in separation and recovery of palladium from High Level Liquid Waste (HLW) solutions. Hydrolysis of T(2EH)TDGA solvent system with nitric acid was not observed. Moreover, unlike other “S” donor extractants used for the said purpose, the oxidation of thioetheric sulphur to sulphoxide or sulphones was also not observed. However, radiolytic degradation was notably observed and found to increase with increase in absorbed dose. n-dodecane was found to sensitize the degradation of T(2EH)TDGA. At gamma radiation dose of 0.2 MGy, no significant loss of T(2EH)TDGA was observed. The degradation products were identified by GC-MS. The major products were found to be formed by cleavage of thioetheric and amidic bonds of T(2EH)TDGA molecule. The extraction studies of palladium with irradiated solvent indicate that with 0.025 M T(2EH)TDGA/n-dodecane, there was no significant change in DPd up to an absorbed dose of 0.2 MGy above which it decreases significantly. However, with 0.05 M T(2EH)TDGA/n-dodecane, there is gradual decrease in DPd with increase of absorbed dose. Further, the radiolysis does not affect the stripping behavior of palladium. Extraction studies of Pd(II) and other fission products from simulated high level liquid waste (SHLW) solutions to irradiated solvent system showed that, except palladium, any other element is hardly extracted thus retaining its remarkable selectivity.

Novel imino diacetamide styrene divinyl benzene resin for separation of 99molybdenum from irradiated uranium–aluminium alloy

Imino diacetamide styrene divinyl benzene (IDAA SDVB) resin was synthesized and evaluated for separation of molybdenum (Mo) from simulated dissolver solution of irradiated uranium–aluminium alloy. Detailed studies were carried out to understand the influence of various parameters on sorption of Mo. The kinetics of Mo sorption is found to be fast and the kinetics data fit well to the pseudo-second order kinetic equation. Sorption of Mo is found to decrease with the increase of feed acidity. The loading capacity of resin is determined to be 30 mg g−1, the sorption isotherm data fit well to the Langmuir model. Batch sorption experiments with simulated dissolver solution showed quantitative uptake of Mo along with some co-extraction of iodine (I). Column runs have demonstrated that co-extracted ‘I’ could be scrubbed easily with solutions of feed acidity. Finally, sorbed Mo could be eluted with 3.0 M HNO3. XAFS and FT-IR studies of Mo sorbed on to IDAA SDVB resin have shown that Mo is sorbed in the +6 oxidation state (in the form of MoO42−), wherein the complex attains octahedral geometry with contribution from four oxygen atoms of the molybdate anion and two oxygen atoms of the amidic moiety of the imino-diacetamide ligand.

Stability studies of N,N,N´,N´-tetra-(2-ethylhexyl) dithiodiglycolamide (DTDGA)

Abstract DTDGA solvent system was evaluated for hydrolytic and radiolytic stabilities to ascertain its application in separation and recovery of palladium from High Level Liquid Waste (HLW) solutions. Hydrolysis of DTDGA solvent system was not observed when it was kept in contact with 3.0 M nitric acid solution for two weeks. Moreover, contrary to other ‘S’ donor extractants used for the said purpose, the oxidation of thioetheric sulphur to sulphoxide or sulphones was also not observed. On the other hand, radiolysis of DTDGA solvent system was notably observed, which was found to increase with increase in absorbed dose. At gamma radiation dose of 0.2 MGy, no significant loss of DTDGA was observed. Aliphatic diluent namely n-dodecane was found to have sensitization effect on degradation of DTDGA. The degradation products were identified by GC-MS, the major ones were found to be formed by cleavage of thioetheric and amidic bonds of DTDGA molecule. The liquid–liquid extraction studies of palladium with irradiated solvent indicate that there was no significant change in DPd up to an absorbed dose of 0.2 MGy above which it decreases gradually. Further, the radiolysis does not affect the stripping behavior of palladium. Extraction studies of Simulated High Level Liquid Waste (SHLW) elements with irradiated solvent system showed that, except palladium, any other element is hardly extracted thus retaining its remarkable selectivity.