Function Of Nitric Acid Concentration Research Articles

Multiplicity of Th(IV) and U(VI) HEH[EHP] Chelates at Low Temperatures from Concentrated Nitric Acid Extractions

Organophosphorus extractants have been widely investigated for lanthanide recovery from ore and for application in the reprocessing of spent nuclear fuel, such as in Advanced TALSPEAK schemes. Determining the speciation of the extracted metal complex in the organic phase remains a significant challenge. A better understanding of the variability of HEH[EHP]-actinide complexes and the speciation of chelates for tetra- and hexavalent actinides can improve the predictability of actinide phase transfer in such biphasic systems. In this study, the extraction of Th(IV) and U(VI) from nitric acid media using HEH[EHP] in heptane is examined. The distribution ratio as a function of nitric acid concentration was quantified using UV-vis spectroscopy, and then the speciation of HEH[EHP]-metal complexes in the organic phase was investigated using Fourier transform infrared (FTIR) spectroscopy and low-temperature 31P nuclear magnetic resonance (NMR) spectroscopy. In addition to perturbation of the vibrational modes proximal to the phosphonic moiety in HEH[EHP] in the FTIR spectra, the appearance of a nitrate signal was found in the organic phase following extraction from the highest acidity conditions for U(VI). The 31P NMR spectra of the organic phase at a low temperature (-70 °C) exhibited a surprising number (n) of resonances (n ≥ 7 for Th(IV) and n ≥ 11 for U(VI)), with the distribution between these resonances changing with the initial concentration of nitric acid in the aqueous phase. These results indicate that the compositions of the inner and outer spheres of the extracted actinides in the organic phase are more diverse than initially thought.

Effects of nitric acid concentration for nitration of fused [1,2,5]oxadiazolo[3,4-d]pyrimidine-5,7-diamine.

Nitration reactions are very often used for the selective synthesis of novel, high performing nitramine-based materials. Now nitration reactions of the fused 5,7-diamino pyrimidine derivative 1, under different nitric acid concentrations were examined. Concentrated nitric acid gave selectively N-(5-amino-4,5-dihydro-[1,2,5]oxadiazolo[3,4-d]pyrimidin-7-yl)nitramide, 2, while the fused ring nitrate salt, 4, and ring open nitrate salt, 3 were obtained using low concentrations of nitric acid (<70%). In addition, the cesium salt of the fused nitramine derivative 5 was synthesized. All new compounds were isolated in high yields and comprehensively characterized by NMR, FTIR spectroscopy, and elemental analyses. The molecular structures of 2, 3, and 5 were analyzed by single X-ray crystallographic data. These compounds have high calculated heats of formation and high crystal densities. Detonation properties for compounds 2 and 3 were calculated using EXPLO5 software. Fused ring compound 2 (vD, 8549 m s-1; P, 29.62 GPa), and nitrate salt, 3 (vD, 8392 m s-1; P, 29.37 GPa) have superior detonation properties compared with TNT (vD, 7303 m s-1; P, 21.30 GPa). In addition, electrostatic potentials, two-dimensional (2D)-fingerprints, and Hirshfeld surface analysis were used to predict the sensitive properties of compounds 2 and 3. The experimental sensitives suggest possible applications with insensitive energetic applications.

Hydrolytic degradation of tri-iso-amyl phosphate-dodecane system

A solution of 1.1 M tri-iso-amyl phosphate (TiAP) in n-dodecane (n-DD) has been proposed as a candidate solvent for reprocessing of spent nuclear fuel arising from fast reactors. Significant amounts of radioruthenium are produced as a fission product in fast reactors. To minimize the extraction of radioruthenium during the separation of uranium and plutonium, it was proposed to carry out the solvent extraction process at nitric acid concentration ranging from 4 to 5 M. Under these process conditions, it is quite likely that the solvent phase can undergo hydrolytic degradation, which can cause significant changes in the physicochemical properties of the solvent phase and hamper the recovery of uranium and plutonium. In view of this, the hydrolytic degradation of 1.1 M TiAP/n-DD was studied as a function of nitric acid concentration, duration of degradation and process temperature. The physicochemical properties of the hydrolytically degraded organic phase such as density, viscosity, interfacial tension, phase disengagement time was studied and compared with those obtained for thermally degraded solvent (in the absence of nitric acid) and neat solvent phase. The degree of damage was assessed by the uranium retention test in the hydrolytically degraded solvent phase and the procedure for the removal of degradation products from the organic phase was reported. The results revealed that hydrolytic degradation resulted in the formation of acidic degradation products of both TiAP and n-DD. While most of the acidic degradation products arising from TiAP appears to be washable by sodium carbonate during clean-up, a small amount of hydrocarbon degradation products, e.g. nitrolic acid, sparingly soluble in sodium carbonate seems to retain uranium in organic phase during recovery. The formation of nitration degradation products was confirmed by FT-IR spectroscopy. The recovery of uranium was more that 95% after the clean-up of degraded solvent.

Unexpected Coordination Modes of Bisphosphoramides with Lanthanum(III) and Thorium(IV) Salts: Synthesis, Structural Characterization, Stability, and Extraction Studies

AbstractA series of bisphosphoramides of the type R2P(O)NHCH2CH2NHP(O)R2 (L) (where R=n‐butyl, n‐hexyl, n‐octyl, ethoxy, phenyl) is synthesized in two‐steps by Atherton‐Todd reaction of ethylenediamine and H‐phosphonate derived from the reaction of diethylphosphite and the Grignard reagent. These ligands were employed in the preparation of La(III) and Th(IV)complexes of the general type [LaCl3(L)2]n and [Th(NO3)4Th(IV)2]. Notably, La(III) complexes of bisphosphoramides are found as infinite coordination polymers with bridging phosphine oxide ligands in an intermolecular fashion. In contrast, Th(IV) complexes are formed with two chelating bisphosphoramide ligands around the metal center intramolecularly. All these ligands and the corresponding metal complexes are characterized by spectroscopic and analytical data. The single‐crystal X‐ray analyses of lanthanum and thorium complexes each confirm the coordination modes. Further, these ligands were evaluated to check the extraction behavior with Am(III), U(VI), Th(IV), and Pu(IV) as a function of nitric acid concentration.

Interference of Zr(IV) during the extraction of trivalent Nd(III) from the aqueous waste generated from metallic fuel reprocessing

Abstract A metallic alloy of uranium–zirconium and uranium–plutonium–zirconium has been proposed as a fuel for fast reactors, owing to the possibility of achieving high breeding ratio in a short span of time. About 6–10 wt.% of zirconium has been added to these actinide fuels to increase the melting temperature and thermal-mechanical stability. Aqueous reprocessing of the spent metallic fuel generates the high-level liquid waste (HLLW) that contains about 60 % of the total zirconium from the fuel. In view of this, the extraction behavior of a trivalent representative ion, Nd(III) in the presence of Zr(IV) was studied from nitric acid medium using the candidate ligands proposed for trivalent actinide separation from HLLW, such as N,N,N′N′-tetraoctyldiglycolamide (TODGA), and N,N-di-octyl-2-hydroxyacetamide (DOHyA). The extraction was studied as a function of nitric acid concentration, zirconium and neodymium concentration and Nd(III) to Zr(IV) ratio. The findings of dynamic light scattering (DLS) and ATR-FTIR spectral techniques were used for understanding the complex chemistry of Zr(IV) extraction under different conditions. Poor extraction of nitric acid, smaller aggregate size, no third phase formation during the extraction of Zr(IV) and Nd(III) and other unique solvent properties favor the DOHyA molecule in n-dodecane as a solvent for partitioning of trivalent actinides from HLLW generated from metallic fuel reprocessing.

Investigation on the radiolytic stability of polybenzimidazole-based polymeric resins for the recovery of lanthanides, actinides, palladium from aqueous medium

Radiolytic stability of polymeric resins is an important aspects in nuclear materials processing. The different dosage of gamma radiation was subjected to meta-polybenzimidazole (m-PBI), para-polybenzimidazole (p-PBI) and pyridine-m-PBI based polymeric resins, which was taken for the present radiolytic stability investigation. Irradiated polymers were characterized by FT-IR, SEM and TGA analysis. Extraction of U(IV) and Pd(II) as a function of nitric acid concentration using 50, 100 and 150 kGy gamma irradiated polymeric resins was carried out and static capacity was also investigated for the gamma irradiated polymeric resins and compared with their unirradiated ones. In addition, the extraction behaviour of radionuclides, namely, plutonium, americium and europium as a function of HNO3 concentration utilizing both unirradiated and 150 kGy gamma irradiated polymeric resins was studied for the first time. Results indicated that FT-IR spectra of both unirradiated and 150 kGy irradiated resins are similar. TGA analysis revealed 50% and 20% weight loss for pyridine-m-PBI, m-PBI, respectively. The distribution ratio values decreases with increase in gamma irradiation. The uranium and palladium static capacities were found to be 30 and 182 mg/g resin, respectively. The overall results indicated that p-PBI resin has higher extraction efficiency and exhibits better radiation resistant behaviour as compared to pyridine-m-PBI and m-PBI.

Experimental and theoretical studies on actinide extraction: dibutyl phenyl phosphonate versus tri-n-butyl phosphate

Dibutyl phenyl phosphonate (DBPP) was synthesized by the reaction of phenyl phosphorochloridate with 1-butanol in dichloromethane, in the presence of pyridine as a base. The product was characterized by 13C and 31P NMR, mass spectra and FT-IR spectroscopic techniques. The variation in density of 1.1 M solution of DBPP in xylene was estimated as a function of nitric acid concentration. The conditional acid uptake constant (KH) is a measure of basicity of the ligand. This parameter was evaluated for DBPP and is reported in this paper. Extraction of U(VI), Th(IV) and Am(III) by a 1.1 M solution of DBPP in xylene was studied as a function of nitric acid concentration at 298 K. The distribution ratios of the metal ions in the DBPP/xylene system were compared with that of the tri-n-butyl phosphate (TBP)/n-dodecane system. The stoichiometry of uranyl solvate was evaluated to be 1:2. The extraction studies of some fission products with 1.1 M DBPP/xylene were performed and the distribution ratios (D) were determined. As a final step, we have applied quantum chemical calculations to understand the electronic structure of DBPP and the respective uranium complex, [UO2(NO3)2]·2DBPP. By applying the computationally accurate DLPNO-CCSD(T) methodology, we were able to derive the lowest-energy geometry for [UO2(NO3)2]·2DBPP, where both the nitrate groups are in trans-orientation. The Mulliken population and NBO analysis indicated that for both ligands (TBP and DBPP) the electronic charge is more polarized towards the oxygen atom of P = O group. The net charge at P = O group is positive with a large value estimated for TBP ligand.

Novel diamide ligands with a central carbonyl group and their comparative evaluation with the diglycolamide ligand: synthesis, extraction, DFT and chromatographic studies

Abstract The extraction behaviour of U(VI), Th(IV) and Nd(III) was investigated as a function of nitric acid concentration for diamide based extractants, namely, N,N,N′,N′-tetraoctyl-3-carbonylpentanediamide (TOCPDA) and 4-carbonyl-heptanedioic acid bis-dioctylamide (CHADA). In addition, the distribution ratio was also measured for Pu(IV) and Sr(II) with 1.1 M CHADA in n-dodecane. These extractants were synthesized by adopting simple acid, amine coupling reaction with DCC (dicyclohexylcarbodiimide) and DMAP (N,N′-dimethylaminopyridine) as the coupling agent. The newly synthesized extractants were characterized by FT-IR, NMR, Mass, CHNS and HPLC. The extraction results indicated that CHADA shown has better extraction behavior for U(VI) compared to TOCPDA. In addition, CHADA coated HPLC column was examined for the retention behaviour of U(VI), Th(IV), and Nd(III). Computation studies based on density functional theory (DFT) were carried out to understand the complexing behaviour of U(VI), Pu(IV) and Sr(II) with CHADMA and TMCPDA.

Metal-Promoted Extraction Deprotonation of Bidentate Organophosphoric Reagents: Recovery of Uranium, Thorium, and Lanthanides

The extraction capacities to f elements are studied in a series of bidentate organophosphoric reagents that contain deprotonatable phenol moieties. The dependence of metal [thorium(IV), lanthanum(III), neodymium(III), and holmium(III)] recovery as a function of nitric acid concentration is represented by curves with a maximum, typical of extraction by monodentate organophosphoric reagents. The uranium recovery as a function of acid concentration is presented by curves with a minimum, indicating a change in extraction mechanism from ion exchange to solvation. The quantum-chemical modeling of reagent molecules and their complexes with uranyl ion is carried out. The reagents are structurally similar to reagent V, whose structure was determined by single-crystal X-ray diffraction. The results can be used in the hydrometallurgy of f elements.

Carbamoylmethylphosphine oxide functionalised porous crosslinked polymers towards sequential separation of uranium (VI) and thorium (IV)

A new class of highly crosslinked porous polymeric materials with an ethylene glycol dimethacrylate (EGDMA) backbone appended with carbamoylmethylphosphineoxide (CMPO) ligands has been synthesized via precipitation polymerization. The polymers were characterized by CP-MAS NMR, FT-IR, DSC-TGA, SEM and elemental analysis. The polymers prepared in various porogens were evaluated by nitrogen adsorption/desorption experiments, which revealed the existence of large pore volume and surface areas. The ability of polymers to extract actinides (U, Th, Am) utilizing solid phase extraction (SPE) strategy by batch sorption methods as a function of nitric acid concentration are studied. The crosslinked polymers show - a good sorption ability towards U(VI), Th(IV) and Am(III); − selective extraction of U(VI) over Th(IV); and -high radiolytic stability towards gamma radiation. The effect of porogen on pore structure, sorption kinetics, metal loading, release behavior and recycling studies were also discussed. Sequential and selective separation of U(VI) and Th(IV) was demonstrated by extraction chromatography.

Synthesis and extraction behavior of alkyl and cyclic aminophosphonates towards actinides

Alkyl and cyclic substituted aminophosphonates (AmPs) were synthesized and characterized with various spectroscopic techniques. The molecular structures of diphenyl phenyl aminophosphonate (DPhPhAmP) and diphenyl cyclohexyl aminophosphonate (DPhCyAmP) were elucidated based on the single crystal XRD analysis. Extraction behavior of these synthesized AmPs were investigated with some actinides [U(VI), Th(IV), and Am(III)] and also studied their acid uptake as a function of nitric acid concentration. Here we have compared the extraction behavior of aminophosphonates (AmPs) towards actinides as a function of alkyl, cyclic and alicyclic substituents.

Evaluation of polybenzimidazole-based polymers for the removal of uranium, thorium and palladium from aqueous medium.

Four types of polybenzimidazole (PBI)-based polymers (m-PBI, p-PBI, pyridine-based m-PBI and alkylated m-PBI) have been prepared and characterized. Extraction behaviour of heavy metal ions, viz. U(VI), Th(IV) and Pd(II), with these polymers was investigated. Distribution ratios for the extraction of these metal ions were measured as a function of nitric acid concentration. Extraction data reveal that, in general, p-PBI exhibits a higher distribution ratio for U(VI), Th(IV) and Pd(II) compared with the other polymeric resins evaluated in the present study. Column chromatography experiments were carried out with a solution of U(VI), Th(IV) and Pd(II) in dilute nitric acid media using columns packed with m- and p-PBI polymeric material for understanding the sorption and elution behaviour. The p-PBI-based resin has shown higher palladium sorption capacity (1.8 mmol g−1). The studies also established that p-PBI resin is a potential candidate material for the recovery of U(VI) and Th(IV) (capacity 0.22 mmol g−1 and 0.13 mmol g−1) from an aqueous stream, e.g. mine water samples.

Dissolution behavior of MgO based inert matrix fuel for the transmutation of minor actinides

This study explores the dissolution properties of magnesia-based inert matrix nuclear fuel (IMF) containing transuranium elements (TRU). Pure MgO pellets as well as MgO pellets containing CeO2, as surrogate for TRU oxides, and are considered as model systems for genuine magnesia based inert matrix fuel were fabricated. The aim of this study is to identify conditions at which the matrix material can be selectively dissolved during the head-end reprocessing step, allowing a separation of MgO from the actinides, whereas the actinides remain undissolved. The dissolution behavior was studied in macroscopic batch experiments as a function of nitric acid concentration, dissolution medium volume, temperature, stirring velocity, and pellet density (85, 90, 96, and 99%TD). To mimic pellets with various burn-ups the density of the here fabricated pellets was varied. MgO is soluble even under mild conditions (RT, 2.5 mol/L HNO3). The dissolution rates of MgO at different acid concentrations are rather similar, whereas the dissolution rate is strongly dependent on the temperature. Via a microscopic approach, a model was developed to describe the evolution of the pellet surface area during dissolution and determine a surface normalized dissolution rate. Moreover, dissolution rates of the inert matrix fuel containing CeO2 were determined as a function of the acid concentration and temperature. During the dissolution of MgO/CeO2 pellets the MgO dissolves completely, while CeO2 (>99%) remains undissolved. This study intends to provide a profound understanding of the chemical performance of magnesia based IMF containing fissile material. The feasibility of the dissolution of magnesia based IMF with nitric acid is discussed.

Molecular Hydrogen Yields from the α-Self-Radiolysis of Nitric Acid Solutions Containing Plutonium or Americium.

The yield of molecular hydrogen, as a function of nitric acid concentration, from the α-radiolysis of aerated nitric acid and its mixtures with sulfuric acid containing plutonium or americium has been investigated. Comparison of experimental measurements with predictions of a Monte Carlo radiation track chemistry model shows that, in addition to scavenging of the hydrated electron, its precursor, and the hydrogen atom, the quenching of excited state water is important in controlling the yield of molecular hydrogen. In addition, increases in solution acidity cause a significant change in the track reactions, which can be explained as resulting from scavenging of eaq- by Haq+ to form H•. Although plutonium has been shown to be an effective scavenger of precursors of molecular hydrogen below 0.1 mol dm-3 nitrate, previously reported effects of plutonium on G(H2)α between 1 and 10 mol dm-3 nitric acid were not reproduced. Modeling results suggest that plutonium is unlikely to effectively compete with nitrate ions in scavenging the precursors of molecular hydrogen at higher nitric acid concentrations, and this was confirmed by comparing molecular hydrogen yields from plutonium solutions with those from americium solutions. Finally, comparison between radionuclide, ion accelerator experiments, and model predictions leads to the conclusion that the high dose rate of accelerator studies does not significantly affect the measured molecular hydrogen yield. These reactions provide insight into the important processes for liquors common in the reprocessing of spent nuclear fuel and the storage of highly radioactive liquid waste prior to vitrification.

Uranyl nitrate hexahydrate solubility in nitric acid and its crystallization selectivity in the presence of nitrate salts

The solubility of uranyl nitrate hexahydrate was determined as a function of nitric acid concentration and temperature, and the crystallization yield was calculated. Results showed an increase in crystal formation at lower initial nitric acid concentrations upon cooling a saturated solution of U(VI) from 50 °C to 2 °C, with over 70% recovery of U(VI) mass at all nitric acid concentrations and nearly quantitative recovery starting at 4 M HNO3. A direct correlation between the change in mother liquor volume percent and U mass removal percent was observed. By reducing the cooling rate from roughly 4.0 °C/min to 0.22 °C/min, the separation factor was increased from 3.88 to 15.7 to greater than 81 for the separation of U(VI) from Sr, Cs, and Nd. At the slower cooling rate, the separation factors were measured as a function of acidity for 2.0–4.3 M HNO3, showing a decrease in selectivity with a decrease in the acidity. There was also no indication that tetravalent metal double-salt precipitation occurred with either Zr4+ or Ce4+. These results indicate that a high-yield, high purity hexavalent actinide crystallization scheme may offer attractive benefits for nuclear-fuel recycle in that only a single very simple and well-understood technology is employed, and the use of organic compounds and solvents is avoided.

Extraction of uranium(VI) from nitric acid solutions using N,N-dihexyloctanamide in ionic liquids: Solvent extraction and spectroscopic studies

ABSTRACTLiquid-liquid extraction studies of uranium(VI) were carried out from nitric acid medium using di-n-hexyloctanamide (DHOA) in several room-temperature ionic liquids (RTIL). The extraction of the metal ion as a function of nitric acid concentration showed different trends based on the alkyl substituents of the RTIL. While the DU values decreased with increasing HNO3 concentration (up to ca. 0.5 M) with [C4mim][NTf2] and [C6mim][NTf2], almost no change was seen with [C8mim][NTf2]. This suggested that while a cation-exchange mechanism is operative with the former diluents, which was to a much lower extent for the latter. The extracted species were found to contain about 2 molecules of DHOA from the feed solutions containing either 0.01 M and 4 M HNO3, which was arrived at from the ligand-concentration-variation experiments. Recycling studies were also performed by carrying out stripping and radiolytic stability studies. The nature of the extracted species as ascertained from the UV-visible spectrophotometry studies indicated similarity between the extracts obtained in RTIL medium, which were entirely different from that observed with n-dodecane as the diluent.

Highly efficient and eco-friendly extraction of neodymium using, undiluted and non-fluorinated ionic liquids. Direct electrochemical metal separation

Abstract A new approach for highly efficient extraction and recovery of neodymium from acidic medium by new undiluted ionic liquids (ILs) as extractants. The distribution ratio DNd and the extraction efficiency %E was measured as a function of nitric acid concentration, extraction time, nature of the IL, concentration of the aqueous feed and molar quantity of complexing agent. DNd is higher than 105 and %E is close to 100% when the HNO3 concentration is greater than 6 M. The extraction process follows solvation mechanism, suggesting the involvement of three molecules in the extraction of one (Nd3+)-nitrate complex. The nature of bonding in the extracted complexes was investigated by various spectroscopic techniques. The recovery process, of metal was performed by direct electrodeposition from the IL phase. The electrodeposition of metal was realized by potentiostatic electrolysis at −2 V. The current efficiency evaluated from the mass change of the anode was more than 83%. The particles were obtained as small crystallite rods with various size approximately 3–70 μm and diameters range of 0.5–30 μm. The liquid-liquid extraction and the direct electrodeposition of neodymium by these H-phosphonate based ILs, are new efficient and eco-friendly process.

Composite polymeric beads containing N,N,N′,N′-tetraoctyldiglycolamide for actinide ion uptake from nitric acid feeds: Batch uptake, kinetic modelling and column studies

Polyethersulphone (PES) based composite polymeric beads (CPB) containing TODGA (N,N,N′,N′-tetraoctyldiglycolamide) as the extractant were prepared by conventional phase inversion technique and were tested for the uptake of actinide ions such as Am3+, UO22+, Pu4+, Np4+ and fission product ions such as Eu3+ and Sr2+. The CPBs containing 2.5–10wt.% TODGA were characterized by various physical methods and their porosity, size, surface morphology, surface area and the degradation profile by thermogravimetry were analyzed. The batch uptake studies involved kinetics of metal ion sorption, uptake as a function of nitric acid concentration, kinetic modelling and adsorption isotherms and most of the studies involved the Am3+ ions. The batch saturation sorption capacities for Eu3+ loading at 3M HNO3 were determined to be 6.6±0.02, 9.1±0.02 and 22.3±0.04mgg−1 of CRBs with 2.5wt.%, 5wt.% and 10wt.% TODGA, respectively. The sorption isotherm analysis with Langmuir, D–R and Freundlisch isotherms indicated chemisorption monolayer mechanism. Chromatographic studies indicated breakthrough of Eu3+ (using a solution containing Eu carrier) after about 0.75 bed volume (3.5–4mL). Elution of the loaded Eu was carried out using 0.01M EDTA as the eluent.

Supercritical fluid extraction of uranium and thorium from nitric acid medium using organophosphorous compounds

Abstract In recent years, Supercritical Fluid Extraction (SFE) technique has been widely used for the extraction of metal ions. In the present study, extraction of uranium from nitric acid medium was investigated using supercritical carbon dioxide (Sc-CO2) containing various organophosphorous compounds such as trialkyl phosphates e.g. tri-iso-amyl phosphate (TiAP), tri-sec-butyl phosphate (TsBP) and tri-n-butyl phosphate (TBP), dialkylalkyl phosphonates, e.g. diamylamyl phosphonate (DAAP) and dibutyl butyl phosphonate (DBBP), dialkyl hydrogen phosphonates, e.g. dioctyl hydrogen phosphonate (DOHP), dioctylphosphineoxide (DOPO), trioctyl phosphine oxide (TOPO), n-octylphenyl N,N-diisobutyl carbamoylmethylphosphine oxide (CMPO) and di-2-ethyl-hexyl phosphoric acid (HDEHP). Some of these ligands have been investigated for the first time in the supercritical phase for the extraction of uranium. The extraction efficiency of uranium was studied with TiAP, DAAP and DBBP as a function of nitric acid concentration; the kinetics of the equilibration period (static extraction) and transportation of the metal complex (dynamic extraction) was investigated. The influence of pressure and temperature on the extraction behaviour of uranium with DAAP was studied from 4 N HNO3. The extraction efficiency of uranium from 4 N nitric acid medium was found to increase in the order of phosphates &lt; phosphonates &lt; HDEHP &lt; TOPO &lt; CMPO. In the case of phosphates and phosphonates, the maximum extraction of uranium was found to be from 4 N HNO3 medium. The acidic extractants, HDEHP and DOHP showed relatively higher extraction at lower acidities. The relative extraction of uranium and thorium from their mixture was also examined using Sc-CO2 containing phosphates, phosphonates and TOPO. The ligand, TsBP provided better fractionation between uranium and thorium compared to trialkyl phosphates, dialkyl alkyl phosphonates and TOPO.

Insights Into the Extraction of Am(III) by Aliquat-336 Based Ionic Liquids

The extraction behavior of Am(III) in a solution of tetra-(2-ethylhexyl)diglycolamide (TEHDGA) in n−dodecane (n−DD) or toluene was studied as a function of nitric acid concentration. The distribution ratio of Am(III) in 0.1 M TEHDGA/molecular diluent increased with increase in the concentration of nitric acid. Since the Aliquat-336 based ionic liquid namely, tri-n-octylmethylammonium di-(2-ethylhexyl)phosphate ([A336]+[DEHP]−) was miscible in molecular diluents such as n-DD and toluene, the extraction behavior of Am(III) in TEHDGA/molecular diluent was investigated in the presence of small concentrations of ionic liquid to understand the role of ionic liquid in extraction. The distribution ratio of Am(III) in 0.2 M [A336]+[DEHP]−/molecular diluent was negligible. Significant increase in distribution ratio of Am(III) was observed when [A336]+[DEHP]− was added to 0.1 M TEHDGA/molecular diluent. Since [A336]+[DEHP]− was converted into its components, namely tri-n-octylmethylammonium nitrate ([A336]+[NO3]−) and di-(2-ethylhexyl)phosphoric acid (HDEHP) when contacted with nitric acid, the extraction behavior of Am(III) in 0.1 M TEHDGA/molecular diluents was also studied in the presence of [A336]+[NO3]− and HDEHP to elucidate the mechanism of extraction. The study confirmed that the extraction of Am(III) in ionic liquid medium was controlled by constituents of ionic liquid and the distribution ratio of Am(III) obtained in organic phase was due to the resultant of contributions of ionic liquid constituents.