Search Results

You are looking at 1 - 10 of 17 items

  • Author: N. Sivaraman x
Clear All Modify Search

Abstract

Earlier studies carried out in our laboratory indicated that Tri-sec-butyl phosphate (TsBP) is a potential extractant for U/Th separation. Also, the third phase formation tendency of TsBP is lower compared to its isomers, Tri-n-butyl-phosphate (TBP) and Tri-iso-butyl phosphate (TiBP). In this context, the extraction and third phase formation behaviour of 1.1 M solutions of TiBP and TsBP in n-dodecane in the extraction of Th(IV) from 1 M HNO3 at 303 K over a wide range of Th concentrations were investigated in the present study and the results are compared with the literature data on TBP system. Concentrations of Th(IV) and HNO3 loaded in the organic phase before third phase formation (biphasic region) as well as in third phase and diluent-rich phase after third phase formation (triphasic region) were measured as a function of equilibrium aqueous phase Th(IV) concentration. The density of loaded organic phase was also measured at various Th(IV) concentrations. The extraction profiles in the biphasic region indicated that extraction of Th(IV) by TBP is higher than that of TiBP which in turn is higher than that of TsBP. Extractant concentration in the diluent-rich phase and third phase was measured for the triphasic region.

Abstract

The retention behaviour of uranium, thorium, americium and lanthanides has been investigated, using a reverse phase C18 column modified with 2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine (n-Pr-BTP) with the aim of investigating rapid lanthanide-actinide separations by HPLC technique. Nitric acid and α-hydroxy isobutyric acid (α-HIBA) have been employed as the mobile phase. The influence of mobile phase pH and concentration on the retention of metal ions has been studied. The aim of this study is to investigate the use of BTP coated reverse phase columns as analytical columns for the fast separation of the minor actinides from the lanthanides in the high-level waste (HLW), and to explore whether such columns can be used on a preparative scale for the purification and the recovery of minor actinides from the high-level waste (HLW). It was observed that reverse phase columns modified with BTP showed greater affinity for actinides but exhibited no retention for lanthanides and the lanthanide-actinide separations could be achieved in nitric acid mobile phase, without the need for complexing agents. Americium was separated from the lanthanides with good peak profile and baseline resolution in both nitric acid as well as α-HIBA as the mobile phase. Based on this, the separation of americium from the lanthanides in the HLW was also demonstrated. The retention of a significant amount of thorium by the column in breakthrough studies also indicated that these columns can be used for preparative scale purification of the actinides.

The extraction of plutonium from tissue paper matrix was carried out using supercritical carbon dioxide (Sc-CO2). The removal of plutonium was also studied from other matrices such as teflon, glass and stainless steel. Initial experiments were carried out under subcritical conditions. Supercritical extraction conditions were also employed in some experiments for the recovery of plutonium from tissue paper matrix. Complete extraction of Pu(III) as well as Pu(IV) in their nitrate form from tissue paper was achieved for the first time using supercritical carbon dioxide modified with n-octyl(phenyl)-N,N-diisobutyl carbamoylmethyl phosphine oxide (φCMPO) in methanol. Pu(IV) was also completely removed from other matrices such as teflon, stainless steel and glass. Studies on the extraction of Am(III) using supercritical carbon dioxide modified with CMPO in methanol resulted in its complete recovery from tissue paper.

Abstract

Burn-up measurement for the fast reactor fuels in general and measurements on short cooled dissolver solutions in particular pose a great challenge due to the high level of radioactivity associated with the solution. An HPLC technique using monolith support has been developed for the first time for the determination of burn-up of fast reactor fuels and applied to the dissolver solution of the FBTR (Fast Breeder Test Reactor, Kalpakkam, India) fuel discharged at nominal burn-up of 150 GWd/t. A dynamic ion-exchange technique developed for the individual separation of lanthanides as well as actinides in connection with the burn-up measurements, has led to separation of all 14 lanthanides in about 2.77 min, the fastest LC technique as of now in literature and has resulted in a significant reduction in analysis time, radiation dose to operator and liquid waste generation. The dissolver solution was injected directly into the HPLC and assayed for lanthanide fission products, uranium, and plutonium using appropriate dilutions. The atom percent fission was calculated based on these measurements and the results are discussed. A reversed-phase chromatographic technique was also employed for the determination of uranium and plutonium in the dissolver solution. The sorption behaviour of uranium and thorium was examined on a monolith support modified with bis-2-ethylhexyl succinamic acid (BEHSA). Rapid separation of uranium from thorium could be achieved in about 20 s on the modified monolith support.

Summary

The removal of uranyl nitrate from tissue matrix has been studied with supercritical carbon dioxide modified with methanol alone as well as complexing reagents dissolved in methanol. A systematic study of various complexing agents led to the development of an extraction procedure for the quantitative recovery of uranium from tissue matrix with supercritical carbon dioxide modified with methanol containing small quantities of acetylacetone. The drying time and temperature employed in loading of uranyl nitrate onto tissue paper were found to influence the extraction efficiency significantly.

Summary

Extraction of uranium from tissue matrix was studied using supercritical carbon dioxide containing modifier solvent. The extraction efficiency was investigated with carbon dioxide containing methanol, tri-n-octyl phosphine oxide (TOPO) in methanol and tri-n-butyl phosphate (TBP) in methanol as modifiers. The extraction behaviour of the UO2(NO3)2 · 2TOPO complex loaded on tissue was also investigated. Supercritical carbon dioxide modified with methanol alone was found to extract a maximum of about 76% uranium from tissue matrix.

Abstract

This paper presents the results on the use of short columns (3−5 cm long) with small particle size (1.8 μm) for high performance liquid chromatographic separation of individual lanthanides and uranium from plutonium as well as uranium from thorium to achieve rapid separations i.e. separation time as short as 3.6 min for individual lanthanides, 1 min for thorium-uranium and 4.2 min for uranium from plutonium. These advantages can be exploited to significantly reduce analysis time, liquid waste generation as well as dose to operator when radioactive samples are analysed e.g. burn-up determination.

In the present work, a dynamic ion-exchange chromatographic separation technique was employed using camphor-10-sulfonic acid (CSA) as the ion-pairing reagent and α-hydroxy isobutyric acid (α-HIBA) as the complexing reagent for the isolation of individual lanthanides as well as the separation of uranium from thorium.

Uranium was separated from Pu(III) as well as Pu(IV) by reverse phase HPLC technique. The reverse phase HPLC was also investigated for the isolation and quantitative determination of uranium from thorium as well as lanthanide group from uranium.

The dynamic ion-exchange technique using small particle support was demonstrated for measuring the concentrations of lanthanide fission products such as La, Ce, Pr, Nd and Sm in the dissolver solution of fast reactor fuel. Similarly, the assay of uranium in the dissolver solution of fast reactor was carried out using reverse phase HPLC technique. The rapid separation technique using reverse phase HPLC was also demonstrated for separation of lanthanides as a group from uranium matrix; samples of LiCl-KCl eutectic salt containing chlorides of lanthanides in uranium matrix (typically 1:2000) were analysed.

Abstract

A novel method has been developed for the controlled delivery of various ligands including solid extractants using supercritical carbon dioxide (Sc-CO2). A ligand delivery vessel with a restricted geometry where its inlet and outlet are located beside each other, accomplished the task of the controlled delivery of ligands. The proposed method eliminates the usage of modifier solvent such as methanol for the delivery of various ligands during the supercritical fluid extraction of metal ions. Using neat Sc-CO2, the delivery profiles for the various ligands such as octyl(phenyl)-N,N-diisobutylcarbamoylmethyl-phosphineoxide (CMPO), tri-n-butyl phosphate (TBP), tri-n-octyl phosphine oxide (TOPO), theonyltrifluroacetone (TTA) and di(2-ethylhexyl)isobutyramide (D2EHIBA) were established. The delivery profiles were optimised by investigating the influence of various extraction parameters such as ligand delivery vessel geometry, temperature, pressure, flow rate of Sc-CO2 and ligand content. Applications of these ligand delivery modes were demonstrated for the supercritical fluid extraction of uranium from tissue paper matrix and preferential extraction of uranium over thorium. These results are compared with the extraction studies involving methanol or hexane modifier under similar experimental conditions. The extraction of neodymium nitrate was also demonstrated using modifier free delivery mode.

Abstract

The present study describes a correlation that is developed from retention of lanthanide and actinide complexes with the stability constant. In these studies, an ion-pairing reagent, camphor-10-sulphonic acid (CSA) was used as the modifier and organic acids such as α-hydroxy isobutyric acid (α-HIBA), mandelic acid, lactic acid and tartaric acid were used as complexing reagent for elution. From these studies, a correlation has been established between capacity factor of a metal ion, concentration of ion-pairing reagent and complexing agent with the stability constant of metal complex. Based on these studies, it has been shown that the stability constant of lanthanide and actinide complexes can be estimated using a single lanthanide calibrant. Validation of the method was carried out with the complexing agents such as α-HIBA and lactic acid.

It was also demonstrated that data from a single chromatogram can be used for estimation of stability constant at various ionic strengths. These studies also demonstrated that the method can be applied for estimation of stability constant of actinides with a ligand whose value is not reported yet, e.g., ligands of importance in the lanthanide–actinide separations, chelation therapy etc. The chromatographic separation method is fast and the estimation of stability constant can be done in a very short time, which is a significant advantage especially in dealing with radioactive elements. The stability constant data was used to derive speciation data of plutonium in different oxidation states as well as that of americium with α-HIBA. The elution behavior of actinides such as Pu and Am from reversed phase chromatographic technique could be explained based on these studies.