T. G. Srinivasan

The Effect of the Structure of Trialkyl Phosphates on their Physicochemical Properties and Extraction Behavior

The density of various trialkyl phosphates (TalP) such as tri‐n‐butyl phosphate (TBP), tri‐iso‐butyl phosphate (TiBP), tri‐sec‐butyl phosphate (TsBP), tri‐n‐amyl phosphate (TAP), tri‐2‐methylbutyl phosphate (T2MBP), tri‐iso‐amyl phosphate (tri‐3‐methylbutyl phosphate, TiAP), tri‐sec‐amyl phosphate (tri‐2‐amyl phosphate, TsAP), tri‐cyclo‐amyl phosphate (TcyAP), tri‐n‐hexyl phosphate (THP), and 1.1 M solutions of some of these phosphates in various diluents, solubility of water in trialkyl phosphates, and the aqueous solubility of trialkyl phosphates have been measured. Extraction of nitric acid, Th(IV), and U(VI) by trialkyl phosphates has also been studied by the batch extraction method. Metal‐solvate stoichiometry in the extraction of Th(IV) and U(VI) by some of the phosphates has been evaluated. Data on the extraction of U(VI) by various trialkyl phosphates as a function of equilibrium aqueous‐phase nitric acid concentration at 303 K are presented in this paper. Data on the extraction of Th(IV) and U(VI) from 1 M and 5 M HNO3 by trialkyl phosphates as a function of equilibrium aqueous‐phase metal concentration at 303 K are also presented in this paper. The effects of the structure of trialkyl phosphates on their physicochemical properties and extraction behavior are described in this paper.

Studies on the Use of N,N,N´,N´-Tetra(2-ethylhexyl) Diglycolamide (TEHDGA) for Actinide Partitioning. I: Investigation on Third-Phase Formation and Extraction Behavior

Abstract Diglycolamides have emerged as an interesting class of extractants for actinide partitioning from high-level waste (HLW). N,N,N´,N´-tetraoctyl diglycolamide (TODGA) has been extensively studied for lanthanide-actinide co-extraction behavior. The present work deals with a branched isomer of TODGA, that is, N,N,N´,N´-tetra(2-ethylhexyl) diglycolamide (TEHDGA). TEHDGA was studied for the extraction of 241Am and third-phase formation. The effect of using different phase modifiers on the prevention of the formation of a third phase during nitric acid extraction by TEHDGA along with the acid uptake behavior by TEHDGA in the presence of the modifiers was studied. The modifiers used for this purpose were di(n-hexyl)octanamide (DHOA), isodecanol, and n-decanol. The effect of the modifiers on the uptake of 241Am as a function of acid concentration and as a function of modifier concentration was also examined. DHOA was found to be a suitable modifier, in spite of its high acid uptake. The uptake of lanthanides Ce, La, Eu, Gd, and Nd and elements such as Fe, Ni, Mn, Mo, Ru, Sr, and Cs with DHOA-modified TEHDGA–n-dodecane solvent systems were investigated. The results obtained indicated that, while DHOA-modified TEHDGA/n-dodecane extracted lanthanides and actinides, it did not show any significant uptake of other elements. Thus, the TEHDGA-DHOA/n-dodecane solvent system can be used effectively for the partitioning of lanthanides and actinides from HLW.

A new procedure for the spectrophotometric determination of uranium(VI) in the presence of a large excess of thorium(IV).

Spectrophotometric determination of microgram amounts of U(VI) with 2-(5-Bromo-2-Pyridylazo)-5-diethylaminophenol (Br-PADAP), originally developed by Johnson and Florence has been modified to enable the determination of U(VI) in the presence of a large excess of Th(IV). The effects of thorium, tri-n-butyl phosphate (TBP) and ethanol on the estimation of uranium have been studied in detail and are presented in this paper. This modified method can be applied for the analysis of U(VI) both in aqueous and organic samples containing a large excess of Th(IV) (Th:U = 10000:1).

Parameters Influencing Third‐Phase Formation in the Extraction of Th(NO3)4 by some Trialkyl Phosphates

Third‐phase formation in the extraction of Th(IV) by trialkyl phosphates (TalP) such as tri‐n‐butyl phosphate (TBP), tri‐iso‐butyl phosphate (TiBP), tri‐sec‐butyl phosphate (TsBP), tri‐n‐amyl phosphate (TAP), tri‐2‐methylbutyl phosphate (T2MBP), tri‐iso‐amyl phosphate (TiAP), tri‐sec‐amyl phosphate (TsAP), and tri‐cyclo‐amyl phosphate (TcyAP) has been investigated under various conditions. Formation of a third phase in the extraction of Th(IV) by TBP/n‐dodecane as a function of TBP concentration at 303 K was studied. Measurements were also carried out on the extraction of Th(IV) from its solution with near‐zero free acidity by various phosphate/diluent binary solutions (1.1 M) as a function of temperature. Third‐phase formation in the extraction of Th(IV) by 1.1 M TalP in various diluents from nitric acid media has also been studied as a function of equilibrium aqueous‐phase acidity at 303 K. Empirical equations to predict limiting organic concentration with respect to various parameters for third‐phase formation in the extraction of Th(IV) by TBP and TAP from nitric acid media have been derived. Some of the above phosphates have been investigated for the distribution of Th(NO3)4 between the “diluent‐rich phase” (DP) and “third‐phase” (TP) in the extraction of Th(IV) by 1.1 M TalP in various diluents from its saturated solution with near‐zero free acidity at 303 K. Results of the above studies are presented in this paper. Based on these studies, the effects of extractant concentration, the temperature, the nature of the diluent, the equilibrium aqueous‐phase acidity, and the structure of the extractant on third‐phase formation behavior of trialkyl phosphates are described in this paper.

Studies on U-Th separation using tri-sec-butyl phosphate

ABSTRACT This paper reports data on the extraction of U(VI) and Th(IV) from nitric acid by tri-sec-butyl phosphate (TsBP) and provides a comparison of the extraction behaviour with that of tri-/?-butyl phosphate(TBP). Data on third phase formation in the extraction of thorium nitrate by TsBP from nitric acid medium are also reported for the first time. The results indicate that tri-sec-butyl phosphate is a potential candidate for the separation of U(VI) from Th(IV).

THE EFFECT OF DILUENT ON THIRD PHASE FORMATION IN THORIUM NITRATE - TBP SYSTEM: SOME NOVEL EMPIRICAL CORRELATIONS

The limiting organic phase concentration (LOC) above which a third phase forms, in Thorium Nitrate - 30% TBP/Diluent system has been shown to have a good correlation with some parameters which characterise the diluent such as Connectivity Index, Wiener Number and Diluent Parameter. Aliphatic, alicyclic, aromatic and halocarbon type diluents have been used in this study. The LOC has also been found to be additive for mixtures of diluents. The results make it possible to predict third phase formation in systems where the diluent composition is known.

Studies on the Extraction of Actinides by Diamylamyl Phosphonate

Abstract Diamylamyl phosphonate (DAAP) was synthesised by the Michealis Becker reaction, and was characterized by elemental analysis, IR, and 31P NMR. The extraction of U(VI), Th(IV), Pu(IV) and Am(III) by 1.1 M DAAP in n‐dodecane as a function of nitric acid concentration was studied and the results are compared with the extraction behavior of these ions by tributyl phosphate (TBP) and triamyl phosphate (TAP) in n‐dodecane. Some important physical properties of the extractant that have to be met for its use in industrial scale liquid‐liquid extraction such as density, surface tension, viscosity and phase disengagement time with 1.1 M DAAP/n‐dodecane have been measured and compared with those of 1.1 M TBP/n‐dodecane. Studies on the third phase formation behavior of DAAP/n‐dodecane with U(VI) and Th(IV) nitrates in nitric acid medium have been carried out and the results are reported. The breakthrough and elution behavior of U(VI) using a column packed with 50% (w/w) DAAP impregnated on Amberlite XAD‐7 was studied and reported.

Studies on the extraction behavior of octyl(phenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide in polymeric adsorbent resins

Abstract This paper provides a comparison of the extraction of U(VI) and Am(III) from 3 M HNO3 by Amberlite XAD‐4 and XAD‐7 resins loaded with octyl(phenyl)‐N,N‐diisobutylcarbamoylmethylphosphine oxide (OΦCMPO). The paper also compares the breakthrough behavior during the sorption of Nd(III) and U(VI) from 3 M HNO3 by extraction chromatography using these resins as support material with OΦCMPO as the stationary phase. The data indicate that XAD‐7 is a better support material for extraction chromatographic applications.

THIRD PHASE FORMATION IN EXTRACTION OF THORIUM NITRATE BY MIXTURES OF TRIALKYL PHOSPHATES

ABSTRACT This paper reports the results of the studies on third phase formation during the extraction of thorium nitrate from zero free acidity solutions by mixtures of trialkyl phosphates. The phosphates used are tri n-butyl phosphate(TBP), triiso butyl phosphate(TiBP), tri sec butyl phosphate (TsBP) and tri n-amyl phosphate(TAP). The results indicate that small additions of a homologous phosphate can alter the Limiting Organic Concentration (LOC) above which the third phase formation takes place and thus can be advantageously utilised. Use of mixtures of the trialkyl phosphates as extractant can thus obviate the need for adding modifiers such as alcohols to the organic phase for avoiding third phase formation.

Evaluation of New Anion Exchange Resins for Plutonium Processing

Abstract This paper presents the results of studies comparing the performance of two new anion exchange resins for plutonium processing with the well proven and widely used benchmark, Dowex 1X4 resin. In this connection, the experiments on distribution ratio measurement of plutonium as a function of nitric acid concentration, Pu(IV) sorption kinetics, chemical, thermal, and radiation degradation of the two commercially available anion exchange resins namely, Tulsion A‐PSL 4 and Tulsion A‐PSL 6 have been studied, vis‐à‐vis the benchmark. Tulsion A‐PSL 6 was found to have higher plutonium sorption capacity and polymer matrix stability as well as better kinetics of sorption than the other two resins, while Tulsion A‐PSL 4 and Dowex 1X4 were found to have comparable sorption capacity, kinetics, and resistance to chemical and radiation degradation. The small‐scale evaluation of these new anion exchange resins shows that they can be used for the purification and concentration of plutonium.