J. N. Sharma

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.

Studies on the kinetics of UO2 dissolution in carbonate-bicarbonate medium using sodium hypochlorite as oxidant

The dissolution of UO2 in carbonate-bicarbonate solutions containing sodium hypochlorite as an oxidant has been investigated. The effect of temperature, sodium hypochlorite concentration and stirring speed was examined. In the temperature range of 303 to 318 K, the leaching reaction displayed linear kinetics. Apparent activation energy obtained from the differential approach was found to be 57 kJ mol−1. This relatively high activation energy value indicates a chemically controlled behavior of UO2 dissolution. The order of reaction with respect to sodium hypochlorite concentration was found to be unity.

An amide functionalized calix-benzocrown-6 ionophore for the selective extraction of cesium from highly concentrated nitric acid: the effect of intramolecular buffering

A series of novel calix[4]arene-benzocrown-6 amide (CBCA) ligands in 1,3-alternate conformation having an amide group attached to the aromatic ring of the polyether ring network have been synthesized and evaluated for the extraction of cesium at varying concentrations of aqueous nitric acid. Amide substituted calix-crowns modified with isodecyl alcohol (IDA) and o-nitrophenylhexyl ether (o-NPHE) in n-dodecane have been used for the extraction of cesium and compared to their non-amide analogue viz. calix-benzocrown (CBC). It was observed that the presence of the amide group enhanced the uptake of cesium at high nitric acid concentrations as compared to CBC . This behavior may be attributed to an internal buffering effect of the amide group present in the calix-crowns.

Solvent Extraction Studies of Rare Earths from Thiocyanate Medium with N,N,N´,N´-tetra(2-ethylhexyl) diglycolamide

The extraction behavior of rare earth (RE) elements from thiocyanate medium by N,N,N’,N’-tetra(2-ethylhexyl) diglycolamide (TEHDGA), a neutral extractant, has been investigated and the optimum conditions for their separations were determined. Isodecyl alcohol was used as phase modifier and a concentration of 5%(v/v) was found sufficient to mitigate third phase formation under our experimental conditions. The extraction mechanism of RE with TEHDGA was established by analyzing distribution data with slope analysis technique and showed the formation of a neutral species, RE(SCN)3.2TEHDGA, in the organic phase. The extraction of rare earth decreased with increase in temperature indicating exothermic nature and the enthalpy change (ΔH) obtained for Y(III) was −14.27 kJ/mol. Among various stripping agents studied, oxalic acid was found to be efficient in quantitative stripping of rare earths from TEHDGA. The extraction efficiency for all the rare earths by TEHDGA was also investigated. High separation factor of 6.4 for Er/Y pair at 0.03 M thiocyanate has indicated the feasibility of using TEHDGA as extractant to separate Y from heavy rare earths, in particular Er, from thiocyanate medium.

Potentiometric determination of D2EHPA and M2EHPA using mathematical software for end point determination

The potentiometric estimation of D2EHPA containing M2EHPA of various samples in reagent grade acetone was studied. The differential plot of the results of analysis were determined using ORIGIN mathematical software for end point determination. Visual color indicators were also tested for estimation of D2EHPA and M2EHPA, but the accuracy of measurement was less than the endpoint determination by differential plots.

Dialkylmethyl-2-(N,N-diisobutyl)acetamidoammonium iodide as a ruthenium selective ligand from nitric acid medium

A new class of quaternary ammonium iodide based ligands with 2-(N,N-diisobutyl)acetamide as an alkyl appendage have been designed, synthesized and tested for their ability to extract ruthenium selectively from nitric acid medium. The 2-(N,N-diisobutyl)acetamido ammonium iodide with two propyl and a methyl substituents showed best results for the recovery of ruthenium. The optimized concentration of the solvent was found to be 0.2M in 30% isodecyl alcohol/n-dodecane. The stoichiometry of the complex was ascertained by slope analysis method and was found to be 1:1 with respect to ligand L(+)I(-) and Ru(NO)(NO3)3. Ruthenium formed an adduct of structure LRu(NO)(NO3)3 I in the extraction medium. Iodide ion played an important role in the formation of the stable and extractable complex of ruthenium. No extraction was observed when iodide was replaced by nitrate anion in the ligand. The ligand also showed good selectivity for ruthenium in the presence of other metal ions commonly found in nitric acid solutions of nuclear waste.

α-Dialkylamino N,N-diisobutylacetamides: a new class of anion exchanger with intramolecular buffering properties

A new class of ammonium based anion exchangers embedded with a terminal amide group, viz. α-dialkylamino N,N-diisobutylacetamides has been designed, synthesized and tested for their ability to extract oxometalate anions from nitric acid medium. As a representative example, the molybdate anion has been chosen for the present studies and its extraction behaviour was compared with routinely used anion exchangers like Alamine 336, Aliquat 336 and Primene JMT having no amide functionality. A higher %E value for molybdate was observed with α-dialkylamino N,N-diisobutylacetamides compared to Alamine 336, Aliquat 336 and Primene JMT, from the same HNO3 acidity. The presence of amide group in the ligand is the key to the success of extraction from a relatively higher concentration of nitric acid medium. The amide group in the extractant leads to extra acidity through the intramolecular buffering effect thus enabling the ligand to extract the molybdate anion at higher acidities. Stoichiometry of the ion pair formed during extraction was ascertained by the slope analysis method. The composition of the complex was found to be (LH)2MoO4·HNO3. FTIR and NMR of the loaded extractant indicated that MoO42− is associated with the ammonium site while binding of HNO3 occurred at the amide group.

A new bisglycolamide substituted calix[4]arene-benzo-crown-6 for the selective removal of cesium ion: combined experimental and density functional theoretical investigation

A new bisglycolamide substituted calix-benzo-crown-6 (CBCBGA) ionophore has been synthesized and characterized by using 1H, 13C NMR, ESI-MS and elemental analysis. Detailed investigations on the effect of various parameters such as the aqueous phase acidity, ionophore concentration and nitrate ion concentration on extraction of cesium have been carried out. The new ionophore is found to be highly selective for Cs over other metal ions present in the simulated high level liquid waste solution. The complexing ability of this novel ionophore towards Cs+ and Na+ metal ions was further complimented by predicting the structure, extraction free energy and fraction of charge transfer using the B3LYP density functional employing a split-valence plus polarization (SVP) basis set in conjunction with the conductor like screening model. The unusually high selectivity of CBCBGA for Cs+ ion over Na+ ion was established by the calculated value of difference in the free energy, ΔΔG (ΔGext,Cs+ − ΔGext,Na+), −9.46 kcal mol−1, which is in good agreement with the experimentally determined value of −5.59 kcal mol−1. The calculated values of ρ and ∇2ρ at the bond critical point for the hydrated Na+ ion are found to be reduced during complexation with the CBCBGA, whereas for the hydrated Cs+ ion, though ρ remains same, the value of ∇2ρ is increased which seems to play a decisive role in the higher selectivity to Cs+ ion over Na+ ion of CBCBGA. The new CBCBGA ionophore shows promise for the selective removal of Cs+ ion over other metal ions present in the simulated high level liquid waste solution.

Separation of americium (III) and strontium (II) using TEHDGA and 18-crown-6

Abstract This work describes extraction of Am(III) and Sr(II) together with tetra(2-ethylhexyl) diglycolamide (TEHDGA) and selective back-extraction of strontium with a strontium complexant, 18-crown-6, leading to their separation from each other. 0.3 M TEHDGA+5% isodecyl alcohol/n-dodecane was used to extract Am(III) and Sr(II) from 4 M nitric acid into organic phase with very high D (DAm=1000, DSr=22) and 0.1 M 18-crown-6 dissolved in 4 M nitric acid is used for selective stripping of Sr(II) from loaded extract phase. Am(III) left in the extract phase was then stripped with 0.01 M nitric acid. Stripping of Sr(II) was found to increase with increase in 18-crown-6 concentration, at 0.1 M 18-crown-6 dissolved in 4 M nitric acid, 83% of the loaded strontium (DSr=0.20) was back-extracted in a single contact while loss of Am(III) was 0.8% (DAm=122.45). Stoichiometry limit of 1:1 was observed between strontium and 18-crown-6. Strontium was precipitated and separated from the complexant by Na2SO4 or Na2CO3. This process was tested with simulated solution of high level waste and found suitable for quantitative recovery of strontium with high purity.

Sorption of ruthenium by dipropylmethyl-2-(N,N-diisobutyl) acetamidoammonium iodide impregnated Amberlite XAD-4 resin from nitric acid medium

ABSTRACT Dipropylmethyl-2-(N,N-diisobutyl)acetamidoammonium iodide has been impregnated on Amberlite XAD-4 resin and investigated for sorption of Ru from nitric acid medium. Equilibrium sorption data for Ru uptake were represented well by the Langmuir isotherm equation (R2 = 0.98) compared to Freundlich isotherm equation (R2 = 0.86). The maximum monolayer coverage (Q0) value of 6.25 mg/g as obtained from Langmuir isotherm was close to the experimental value (5.63 mg/g). The heterogeneity parameter (1/n) = 0.37 obtained from the slope of Freundlich isotherm indicates slight heterogeneity in sorption process. Aqueous solutions of 5% ammonia or 10% sodium hydroxide were found suitable for desorption. The method can be applied for separation of Ru from acidic waste solutions.