M. S. Subramanian

SOLVENT EXTRACTION STUDIES ON U(VI), Pu(IV), AND FISSION PRODUCTS USING N,N-DIHEXYLOCTANAMIDE

ABSTRACT The extraction behaviour of nitric acid, uranium(VI), and plutonium(IV) has been investigated using N,N-dihexyloctanamide (DHOA) in n-dodecane. Results indicate that, similar to TBP, the amide extracts HNO3, U(VI), and Pu(IV) as HNO3.DHOA, UO2(NO3)2 2DHOA and Pu(NO3)4.2DHOA, respectively, from moderately acidic solutions (3·5M HNO3). On the other hand at higher acidities (8·5 M HNO3), similar to tertiary amines, anionic species, UO2(NO3)3 − and Pu(NO3)6 2− are extracted as [UO2(NO3)− 3] [HDHOA+] and [Pu(NO3)6 2−] [HDHOA+]2, respectively, by ion-pair formation. The basicity of the amide (KH= 0·188), indicated by the equilibrium constant for the uptake of nitric acid is marginally larger than that of TBP (0·160) The third phase formation in H2O-HNO3-O·5 M DHOA-n-dodecane system occurs when nitric acid concentration in the aqueous phase approaches a value of 9 M. The equilibrium constant values (log Kex) for the formation of UO2(NO3)2 2DHOA and Pu(NO3,)4 2DHOA solvates are evaluated as 1·49 ± 0·01 and 3·55± 0·02 respectively. Preliminary data on temperature effect, extraction and stripping from fission products are also included.

Extraction of plutonium(IV), uranium(VI) and some fission products by di-n-hexyl sulphoxide

The extraction of nitric acid, plutonium, uranium and fission products such as zirconium, ruthenium and europium has been investigated using di-n-hexyl sulphoxide in Solvesso-100. Results indicate that Pu(IV), U(VI), Zr(IV) and Ru NO(III) are extracted as disolvates, whereas Eu(III) is extracted as the trisolvate. The absorption spectra of the plutonium(IV) and uranium(VI) complexes extracted are similar to those of the species extracted by TBP which indicate the similarity of the species involved. Preliminary studies show that irradiated di-n-hexyl sulphoxide extracts zirconium to a smaller extent than irradiated TBP suggesting the use of long chain aliphatic sulphoxides as promising extractants for the recovery of plutonium in high radiation fields.

Complexes of uranyl diketones with aromatic sulphoxides

Abstract The use of sulphoxides as synergist in the solvent extraction of uranyl ion with β-diketones has been investigated by distribution measurements in the system UO22+/HTTA/S, where S is diphenyl or dibenzyl sulphoxide. Results indicate that the sulphoxides exert only a feeble synergetic action which is several orders of magnitude smaller than that of trioctyl phosphine oxide. Values of the equilibrium constants for the system UO22+/HTTA/S are comparable in magnitude to those of the analogous systems with tributyl phosphate. Solid crystalline complexes of the formula UO2X2S (X = anion of theonoyl trifluoroacetone, acetylacetone or dibenzoyl methane) have been isolated. Infrared and proton nuclear magnetic resonance spectra indicate that both the β-diketone moieties in these systems are bidentate. F19 nuclear magnetic resonance spectra however, does indicate some disymmetry in the molecules, UO2(TTA)2TOPO (TOPO = trioctyl phosphine oxide) and UO2 (TTA)2DBSO (DBSO = dibenzyl sulphoxide). This disymmetry is probably caused by the incorporation of the neutral donor molecule into the complex.

Synergistic extraction of uranyl ion with 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (HPMBP) and diphenyl sulfoxide (DPSO), TRI-n-butyl phosphate (TBP) or tri-n-octylphosphine oxide (TOPO)

Synergistic extraction of uranyl ion with 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (HPMBP) and oxo donors with widely varying basicity, viz. diphenyl sulfoxide (DPSO), tri-n-butyl phosphate (TBP) and tri-n-octylphosphine-oxide (TOPO) has been studied at various fixed temperatures. Results indicate that the equilibrium constants in the organic phase for addition reactions (KS) with these donors follow their order of basicity (KH) viz. DPSO (0.033)<TBP (0.16)≪TOPO (8.9) with log KS values of 3.70, 4.28 and 6.45, respectively. The thermodynamic parameters associated with the formation of these systems have been evaluted by the temperature coefficient method. The results indicate that the complex in the organic phase for DPSO and TBP is stabilized only by enthalpy, whereas both enthalpy and entropy contribute to the stabilization of the TOPO complex. Also, enthalpy contribution is more prominent as compared with the UO22+/HTTA/TOPO system, where both enthalpy and entropy contribute almost equally.

Thermodynamics of synergistic extraction of europium(III) by mixtures of thenoyltrifluoroacetone and some neutral oxo-donors

Abstract The synergistic extraction of europium(III) with thenoyltrifluoroacetone (HTTA) and some neutral oxo-donors, viz. diphenyl sulphonide (DPSO), tributylphosphate (TBP) and trioctylphosphine oxide (TOPO) has been studied in benzene. Results indicate that two synergistic species having one and two oxo-donor molecules are simultaneously extracted. The thermodynamic parameters associated with the formation of these two synergistic adducts have been evaluated by the temperature coefficient method which indicate that the reactions are predominantly enthalpy stabilised. Difference in the thermodynamic behaviour of Eu(TTA) 3 ·2TOPO from that of similar adducts with TBP and DPSO has been attributed to possible steric hindrance effects of TOPO.

Solvent Extraction of Plutonium(IV), Uranium(VI), and Some Fission Products with Di-n-octylsulfoxide

Abstract Extraction behavior of plutonium(IV), uranium(VI), and some fission products from aqueous nitric acid media with di-n-octylsulfoxide (DOSO) has been studied over a wide range of conditions. Both the actinides are extracted essentially completely, whereas fission product contaminants like Zr, Ru, Ce, Eu, and Sr show negligible extraction. The absorption spectra of sulfoxide extracts containing either Pu4+ or UO2 2+ indicate the species extracted from nitric acid into the organic phase to be Pu(NO3)4. 2DOSO and UO2(NO3)2. 2DOSO, respectively. Extraction of these actinides decreases with increasing temperature, indicating the extraction to be exothermic. DOSO extracts plutonium and uranium better than di-n-hexylsulfoxide (DHSO) under all condition and is also more soluble in aromatic diluents than the latter. The effect of gamma radiation on the extraction properties of DOSO is found to be similar to that of DHSO.

N,N-Dihexyl Hexanamide: A Promising Extractant for Nuclear Fuel Reprocessing

N,N-Dialkyl amides have drawn the attention of radiochemists engaged in the development of alternate extractants to tri-n-butyl phosphate (TBP) for the reprocessing of irradiated fuels, particularly with high radiation fields and high plutonium content. Dihexyl hexanamide (DHHA) has been found to be a promising extractant in this direction. Log K ex values for the extraction of UO2(NO3)2·2DHHA and Pu(NO3)4·2DHHA in n-dodecane were found to be 1.43 and 3.62, respectively. At high nitric acid concentration (5 M), the amide undergoes protonation and extracts U(VI) and Pu(IV) as ion pairs of the type (UO2(NO3)3 −)(HDHHA+) and (Pu(NO3)6 2−)(HDHHA+)2. At trace level concentrations, the distribution coefficient (D) of Pu(IV) and U(VI) with a 1 M solution of DHHA in n-dodecane at 3.5 M HNO3 are 41.2 and 13.5, respectively. Similarly, at 50% uranium saturation of the organic phase the D values of Pu(IV) and U(VI) are 9.2 and 4.2, respectively. These results suggest the distinct advantages of DHHA over TBP in improved extraction of Pu and ease of stripping of uranium. The separation factors for 0.5 M DHHA at 30 Mrad are obtained as ∼37 (U/Zr) and ∼75 (Pu/Zr), suggesting that this extractant is particularly promising for the selectivity of Pu and U over Zr from irradiated solutions as compared to TBP. Results obtained during this work demonstrate the potential of amides in meeting the challenges posed by the large Pu content and high radiation fields encountered during the reprocessing of Pu-based fuels discharged from thermal as well as fast power reactors.

Extraction behavior of uranium(VI), plutonium(IV) and some fission products with gamma pre-irradiatedn-dodecane solutions of N,N′-dihexyl substituted amides

The extraction behavior of uranium(VI), plutonium(IV) and some fission products like zirconium(IV), ruthenium(III) and europium(III) from 3.5M nitric acid with γ-irradiated organic phase pre-equilibratedn-dodecane solutions of dihexyl derivatives of hexanamide (DHHA), octanamide (DHOA) and decanamide (DHDA) has been investigated as a function of absorbed dose upto 184·104 Gy. The results indicate that the extraction of uranium(VI) decreases gradually with dose upto 72·104 Gy and becomes almost constant thereafter, while, the extraction of plutonium(IV) decreases upto a dose of 20·104 Gy and then increases rapidly up to a dose of 82·104 Gy indicating synergistic effects of radiolytic products formed at higher doses. Extraction of zirconium(IV) increases gradually upto a dose of 72·104 Gy. Europium(III) does not get extracted with any of these amides in the entire dose range (0–184·104 Gy) studied, however, ruthenium shows insignificant increase in extraction with dose. The decrease inD values noticed in the case of plutonium and zirconium after the dose of 72·104 Gy which was attributed to the third phase formation and emulsification. Infrared studies confirm the final products of radiolysis as the respective amines and carboxylic acids. The degraded amide contents have been estimated by quantitative IR spectrophotometric technique. Extraction data obtained for uranium(VI) and plutonium(IV) with TBP/n-dodecane system have also been compared under similar experimental conditions.

Complexes of uranyl β-diketones with aromatic amine N-oxides

Abstract A series of complexes of uranyl β-diketones with pyridine N-oxide (PyNO) and its 4-substituted derivatives (4z·PyNO) have been isolated by solvent extraction. The β-diketones used were thenoyl trifluoroacetone (TTA), benzoyl trifluoroacetone (BTFA), benzoylacetone (BA), dibenzoylmethane (DBM), trifluoroacetylacetone (TFAA) and hexafluoroacetylacetone (HFAA), the 4-substituents of the amine N-oxide ranging from the electron withdrawing NO 2 and Cl to the electron releasing CH 3 and OCH 3 groups. The analytical data for these complexes lead to their formulation as UO 2 (β-diketone) 2 S where S = PyNO or 4z·PyNO. They are monomeric in benzene and non-electrolytes. Characteristic infrared stretching frequencies and proton magnetic resonance spectra of the complexes are reported and discussed in relation to the “substituent parameter” ( σ + ) of the amine N-oxide.

Extraction of uranium(VI) and plutonium(IV) with some aliphatic amides

Extraction of uranium(VI) and plutonium(IV) has been studied with N,N′-dibutyl derivatives of hexanamide (DBHA), octanamide (DBOA) and decanamide (DBDA) at various fixed temperatures of 20, 30, 40 and (50±0.1)°C. The equilibrium constants for the uptake of nitric acid (Kh, a measure of their relative basicities) by these amides were evaluated by the usual method. The equilibrium constants for the extraction of uranium as well as plutonium with all the three amides follow their order of basicity (Kh) viz. DBHA (0.09)<DBOA (0.10)<DBDA (0.13) with log K values of 1.31, 1.43 and 1.73 for uranium and 3.55, 3.65 and 4.17 for plutonium, respectively. It has been observed that whereas uranium(VI) is extracted as a disolvate (similar to TBP and sulfoxides), plutonium(IV) has been found to be extracted as a trisolvate. The thermodynamic parameters evaluated by the usual temperature coefficient method indicate that the extraction reactions of uranium as well as plutonium are stabilized by negative enthalpy change only.