Authors:P. Mithapara, V. Manchanda, and P. Natarajan
Octylphenyl acid phosphate, the commercially available mixture of monooctylphenylphosphoric acid (MOPPA) and dioctylphenylphosphoric acid (DOPPA) in xylene medium has been employed as an extractant for distribution studies on Pu(IV) in different mineral acids including phosphoric acid. It was found possible to extract Pu quantitatively from an acid mixture comprising 2.5M H3PO4, 0.75M H2SO4 and 0.5M HNO3. Quantitative stripping was observed with a mixture of 0.25M oxalic acid and 0.2M ammonium oxalate.
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.
Authors:G. Rama Rao, V. Manchanda, and P. Natarajan
Present work summairzes a method for the estimation of uranium in the presence of plutonium involving the reduction of uranium to U/IV/ and plutonium to Pu/III/ by Zn/Hg/ followed by the selective oxidation of Pu/III/to Pu/IV/with HNO3 catalyzed by molybdate in the presence of large sulphate concenration [5M H2SO4+1.5M /NH4/2SO4]. The oxidation of U/IV/ by K2Cr2O7 is then carried out in the presence of excess of Fe/III/ and Al/NO3/3 to a sharp potentiometric end point. R.S.D. obtained for 20 determinations of uranium /3–6 mg/ was 0.3% in the presence of 0.35 mg of plutonium. Larger quantity for plutonium was found to interfere.
A conductivity method based on differential temperature oxidation of combined carbon and free carbon has been worked out for their determination in uranium carbide employing purified air for oxidation. The combined carbon determined at 550°C and free carbon at 900°C were found to be 4.58% and 0.27% with a precision of 2% and 11%, respectively. The free carbon determined by the present method and that by dissolution followed by conductivity method agreed within ±5%. Effect of temperature and time on the oxidation of free carbon /taken as graphite/ in air atmosphere was also studied.
Authors:N. Gopinath, G. Rama Rao, and P. Natarajan
Ni/III/ has been employed as an oxidant for the quantitative oxidation of plutonium to its hexavalent state and this makes possible to determine plutonium concentrations potentiometrically by the Fe/II/-dichromate redox titration method. The unreacted oxidant is completely reduced by sulphamic acid prior to the determination of plutonium.
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 // increased. The 1g 1 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.
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.
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.
Authors:R. Subba Rao, P. Sivakumar, R. Natarajan, and P. Vasudeva Rao
The transport of hydrochloric acid across a supported liquid membrane using Aliquat 336 in xylene as a carrier was studied. The effect of carrier concentration (0.1–0.6M) on the transportation of hydrochloric acid with and without phase modifier was investigated. The study indicated that the flux of transportation decreased with increasing carrier concentration in the absence of phase modifier. In the presence of phase modifier, however, the flux increased up to 0.2M carrier concentration and started decreasing afterwards. The transportation behavior of hydrochloric acid with and without phase modifier has been attributed to the tendency of aggregation of the carrier.
Authors:J. Shukla, V. Shivarudrappa, P. Mithapara, and P. Natarajan
A highly sensitive and rapid method has been developed for the extraction-spectrophotometric determination of ultra trace amounts of americium. Americium(III) is selectively extracted from 1–10M HNO3 medium with a mixture of (0.3M HDEHP+0.1M P2O5), both dissolved in xylene, and finally estimated in the organic phase itself absorptiometrically employing Arsenazo-III as the chromogenic reagent. A 60% dioxaneethanol mixture was used for optium colour development. Beer's law is obeyed in the concentration range 0.1–0.7 g Am cm–3 and as little as 0.11 g Am cm–3 could be determined with a precision better than ±2%. The molar absorptivity based on Am content is (3.599±0.049)·105 dm3·mol–1·cm–1 at 648 nm which is incidentally the highest value reported as yet for its determination. The optimum concentration range, evaluated by Ringbom's method is 0.1–0.6 ppm Am. Common contaminants such as Al3+, Co2+, Cr3+, Fe3+, Ni2+, Zr4+, F–, NO3–, and SO
in fairly large quantities and moderate amounts of Pu4+, Th4+ and UO
cause no interference in the final assay. Colour development is almost instantaneous and its intensity remains virtually constant for at least 48 hours.