P. R. Natarajan

Extraction of actinides and fission products by octyl(phenyl)-N,N-diisobutylcarbamoylmethyl-phosphine oxide from nitric acid media.

Extraction of promethium(III), uranium(VI), plutonium(IV), americium(III), zirconium(IV), ruthenium(III), iron(III) and palladium(II) has been carried out with a mixture of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and tributyl phosphate (TBP) in dodecane. The effects of nitric acid, TBP and CMPO concentrations on the extraction of these metal ions have been studied. The nature of the species of the above metal ions extracted into the organic phase has been suggested.

Partitioning of actinides from high-level waste streams of purex process using mixtures of CMPO and TBP in dodecane

Abstract The extraction of actinides from high active aqueous raffinate waste (HAW) as well as high-level waste (HLW) solutions arising from Purex processing of thermal reactor fuels has been studied using a mixture of octyl(phenyl)-N N-diisobutylcarbamoyl-methylphosphine oxide (CMPO) and TBP in dodecane. The results on the extraction and stripping of actinides, lanthanides, and other fission products are discussed. Optimum conditions are proposed for the efficient recovery of residual actinides from HAW and HLW streams by CMPO extraction followed by their selective stripping with suitable reagents. Experiments on the extraction and separation of actinides and lanthanides by CMPO in the presence of TBP in dodecane have also been carried out with U(VI) and Nd(III) to arrive at the limiting conditions for avoiding third-phase formation.

Uptake of actinides and lanthanides from nitric acid by dihexyl-N,N-diethylcarbamoylmethylphosphonate adsorbed on chromosorb

Batchwise uptake of Am(III), Pm(III), Eu(III), U(VI) and Pu(IV) by dihexyl-N,N-diethylcarbamoylmethylphosphonate (CMP) adsorbed on chromosorb (CAC) at nitric acid concentrations between 0.01 to 6.0M has been studied. The difference between the uptake behavior of Pu(IV) as compared to other actinides and lanthanides is discussed. The Am(III) and U(VI) species taken up on CAC were found to be Am(NO3)3·3CMP and UO2(NO3)2·2CMP, respectively. The equilibrium constants for the formation of these species have been evaluated and compared with those of similar species formed in liquid-liquid extraction. Batchwise loading of Pm(III) on CAC from 3.0M HNO3 has also been studied.

Tail-end purification of americium from plutonium loading effluents using a mixture of octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide and tri-N-butyl phosphate

The tail-end purification of Am from Pu loading effluents in 7.5M HNO3 containing ∼160 mg l−1 Am and ∼1.2 mg l−1 Pu has been carried out. With 0.2M CMPO+1.2M TBP in dodecane as the extractant and stripping by 0.04M HNO3+0.05M NaNO2, the Pu level is brought down to ∼31.2 μg l−1. When the acidity was reduced to 4.2M HNO3, one contact with 20% TLA/dodecane and subsequent extraction by a mixture of CMPO and TBP and stripping with 0.04M HNO3+0.05M NaNO2 gave Am samples without any detectable amounts of Pu. The recovery of Am was ∼90% by the first procedure and ∼98% by the second one.

Extraction of Am(III) by mixture of dihexyl N,N-diethylcarbamoylmethyl phosphonate and tributyl phosphate in benzene from nitric acid solutions

Extraction of Am(III) by dihexyl N,N-diethylcarbamoylmethyl phosphonate (CMP) in benzene from nitric acid solutions (pH 2.0 to 6.0M) has been studied. High extraction of Am(III) by CMP from 2–3M HNO3 was observed. The species extracted was found to be Am(NO3)3·3CMP. The extraction was also done with mixtures of CMP+TBP and CMP+TOPO, where mixed species were extracted in the organic phase. The back-extraction experiments gave an efficient back-extraction of Am(III) by pH 2.0 (HNO3) from the loaded CMP+TBP phase but a poor back-extraction from the loaded CMP+TOPO phase. The loading of Nd(III) by mixture of CMP and TBP was ∼50% of the CMP concentrations at a total Nd(III) concentration of 0.182M. The thermodynamic parameters of Am(III) extraction by a mixture of CMP and TBP were evaluated by temperature variation method, which suggests that the two-phase reaction is stabilized by enthalpy and opposed by entropy.

Precipitation of plutonium oxalate from homogeneous solutions

A method for the precipitation of plutonium(IV) oxalate from homogeneous solutions using diethyl oxalate is reported. The precipitate obtained is crystalline and easily filterable with yields in the range of 92–98% for precipitations involving a few mg to g quantities of plutonium. Decontamination factors for common impurities such as U(VI), Am(III) and Fe(III) were determined. TGA and chemical analysis of the compound indicate its composition as Pu(C2O4)2·6H2O. Data are obtained on the solubility of the oxalate in nitric acid and in mixtures of nitric acid and oxalic acid of varying concentrations. Green PuO2 obtained by calcination of the oxalate has specifications within the recommended values for trace foreign substances such as chlorine, fluorine, carbon and nitrogen.

Interaction of humic acid with Plutonium/III/

The stability constants of the complex of Pu/III/ with a humic acid at pH 2.9 and 5.0 were measured using solvent-extraction technique. The organic extractant was dinonyl naphthalene sulphonic acid in sodium form /NaD/ in benzene while the humate aqueous phase had a constant ionic strength of 0.5M /NaClO4/. The total carboxylate capacity of the humic acid was determined by direct potentiometric titration to be 6.201 Meq g−1. The apparent pKa increased as the degree of ionization /α/ increased. The 1g β1 values of the complex of Pu/III/ with humic acid have been determined to be 2.8 and 3.11 at pH 2.9 and 5.0, respectively.

Extraction of Pm(III) from acidic solutions using dihexyl N,N-diethylcarbamoylmethyl phosphonate

Benzene solution of dihexyl N,N-diethyl-carbamoylmethyl phosphonate (CMP) has been used for the extraction of Pm(III) from 0.2 to 6.0M HNO3. High extraction of Pm(III) was observed between 2 to 4M HNO3. The species extracted in the organic phase were Pm(NO3)3.3CMP and Pm (NO3)3 (3-n) CMP.nTBP when the extractants were CMP and CMP+TBP, respectively. Pm could be efficiently backextracted from both organic phases by pH 2.0 HNO3 solution.

Studies on the adsorption of plutonium (IV) on alumina from phosphoric acid-nitric acid solution

Results of experiments on the adsorption of plutonium (IV) on alumina and their application to the recovery of plutonium from analytical waste solutions containing phosphoric-nitric acid are reported. Distribution ratios of plutonium (IV) between alumina and solutions containing varying concentrations of phosphoric acid and nitric acid are determined. The influence of various ions like UO22+, Fe3+, MoO42−, VO2+ and SO42− on the distribution ratio is evaluated. Saturation values of adsorption of plutonium (IV) on alumina and optimum conditions for loading and elution of plutonium on a column packed with alumina are described.

Hydrolysis and carboxylate complexation of trivalent americium

Abstract Hydrolysis and complcxation of trivalent americium in the presence of acetic acid and tartaric acid have been studied by solvent extraction. It has been found that in basic solutions (pH 8.0), while hydrolysis of the metal ion predominates in the presence of acetic acid, complexation by the chelating ligand suppresses hydrolysis to some extent. The stability constants for the formation of AmL 2+ (acetate) and AmL 1+ and AmL 2 1− (tartarate) have been determined and the data used for computing the first hydrolysis constant (K 1 *) of Am(III). Using experimentally determined β 1 and K 1 * values, the speciation diagrams for Am(III) in acidic (pH 4.0) and neutral solutions have been deduced.