R. Ruhela

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.

BenzoDODA grafted polymeric resin—Plutonium selective solid sorbent

A new ligand grafted polymeric resin (BenzoDODA SDVB) was synthesized by covalently attaching plutonium selective ligand (BenzoDODA) on to styrene divinyl benzene (SDVB) polymer matrix. BenzoDODA SDVB resin was evaluated for separation and recovery of plutonium(IV) from nitric acid medium. Sorption of Pu(IV) was found to decrease with the increase in nitric acid concentration, with very small sorption above 7.0M HNO3. Sorption kinetics was fast enough to achieve the equilibrium within 60min of contact where the kinetic data fitted well to pseudo-second-order model. Sorption isotherm data fitted well to Langmuir model suggesting chemical interaction between the BenzoDODA moiety and plutonium(IV) ions. Sorption studies with some of representative radionuclides of high level waste showed that BenzoDODA SDVB is selective and therefore could be a promising solid sorbent for separation and recovery of plutonium. Further, the theoretical calculations done on BenzoDODA SDVB resin suggested Pu(NO3)4·BenzoDODA (1:1) sorbed complex conformed to generally observed square antiprism geometry of the plutonium complexes, with contributions from oxygen atoms of four nitrate ions as well as from four oxygen atoms present in BenzoDODA (two phenolic ether oxygen atoms and two carbonyl oxygen atoms of amidic moiety).

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.

Sorption Studies of Uranium on Novel Imino Diacetamide Grafted Styrene Divinyl Benzene Polymeric Resin

Imino diacetamide styrene divinyl benzene (IDAA SDVB) resin was evaluated for the sorption of uranium from sulphuric acid medium. Uranium sorption on to the resin was fast, the kinetic data fitted well in pseudo second order kinetics model. Sorption of uranium was found to increase with the increase in initial concentration of uranium in aqueous feed solution, the sorption isotherm data fitted closely in to Langmuir isotherm model. The sorption of uranium is observed to decrease with the increase in initial feed acidity thereby, allowing sorption and desorption at lower (0.1 M H2SO4) and higher (1.0 M H2SO4) acidities, respectively.

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.

Studies on the use of octyl (phenyl) phosphinic acid (OPPA) for extraction of yttrium (III) from chloride medium

ABSTRACT Extraction behaviour of Y(III) from hydrochloric acid medium by octyl phenyl phosphinic acid (OPPA) has been investigated over a wide range of experimental conditions such as feed acidity, yttrium concentration, OPPA concentration, diluents, temperature, stripping reagents. The extraction mechanism of Y(III) with OPPA was established using distribution data obtained by slope analysis technique and it showed the formation of Y(HA2)3 type of neutral species in the organic phase. This was also confirmed by non-linear least square regression of the distribution data to the mathematical expression correlating percentage extraction and acidity. The extraction constant (log Kex ) of the two phase reaction has been evaluated to be 3.2. Distribution ratio (D) decreased with the increase in temperature with ΔH = –16 kJ/mole. Amongst the reagents studied, 7 M H2SO4 was found to be better with 70% stripping of Y(III) in a single contact. Extraction of Y(III) in different diluents followed the order: dodecane...