Alena Paulenova

Extraction of uranium(VI) with diamides of dipicolinic acid from nitric acid solutions

Abstract Three structural isomers of diamides of dipicolinic acid (N,N′-diethyl-N,N′-ditolyl-dipicolinamide, EtTDPA) with varying position of the methyl group on the tolyl ring have been synthesized and investigated on extractability toward U(VI). The polar diluent FS-13 was used, and distribution ratios of U(VI) were studied as a function of nitric acid, ligand, and lithium nitrate concentrations. Extractability of uranium was shown to increase with increased concentration of nitrate and ligands. Infrared spectra of organic extraction phases indicate that nitric acid is coextracted as part of the neutral metal-ligand complex with U(VI) and EtTDPA through hydrogen bonding with the carbonyl group in the amide moiety.

Extraction of Lanthanides with Diamides of Dipicolinic Acid from Nitric Acid Solutions. I

Abstract Three ortho-, meta-, and para-derivates of ethyl(tolyl)diamides of dipicolinic acid were synthesized and tested on their extraction performance from nitric acids solutions. Extraction of americium and lanthanides (Ln) by these compounds as a function of nitric acid concentration was studied. Distribution ratios of studied metals were determined using ICP-OES method and radiotracer 241Am. Am/Ln separation differs among studied diamides, and the best separation was found for N,N′-diethyl-N,N′-di(ortho)tolyl-diamide.

New Diamides of 2,2′-dipyridyl-6,6′-dicarboxylic Acid for Actinide-Lanthanide Separation

The extraction of americium and lanthanides by diamides of 2,2′-dipyridyl-6,6′-dicarboxilic acid solutions in polar diluents was investigated. The dependence of extraction properties of the diamides on their structure was studied and the distribution ratios of americium and lanthanides from nitric acid solutions were determined. The highest extraction was found for the compounds with the ethyl-group and the alkyl-substituted aryl-group on the amidic nitrogen. The Am/Ln separation factors higher than 10 were achieved for extraction from high acidity media.

Aqueous Complexation of Thorium(IV), Uranium(IV), Neptunium(IV), Plutonium(III/IV), and Cerium(III/IV) with DTPA

Aqueous complexation of Th(IV), U(IV), Np(IV), Pu(III/IV), and Ce(III/IV) with DTPA was studied by potentiometry, absorption spectrophotometry, and cyclic voltammetry at 1 M ionic strength and 25 °C. The stability constants for the 1:1 complex of each trivalent and tetravalent metal were calculated. From the potentiometric data, we report stability constant values for Ce(III)DTPA, Ce(III)HDTPA, and Th(IV)DTPA of log β(101) = 20.01 ± 0.02, log β(111) = 22.0 ± 0.2, and log β(101) = 29.6 ± 1, respectively. From the absorption spectrophotometry data, we report stability constant values for U(IV)DTPA, Np(IV)DTPA, and Pu(IV)DTPA of log β(101) = 31.8 ± 0.1, 32.3 ± 0.1, and 33.67 ± 0.02, respectively. From the cyclic voltammetry data, we report stability constant values for Ce(IV) and Pu(III) of log β(101) = 34.04 ± 0.04 and 20.58 ± 0.04, respectively. The values obtained in this work are compared and discussed with respect to the ionic radius of each cationic metal.

Speciation of Molybdenum (VI) In Aqueous and Organic Phases of Selected Extraction Systems

Abstract The extraction study of molybdenum (VI) by 30% tri-n-butyl phosphate in n-dodecane and 0.2 M octyl (phenyl)-N,N-di-isobutylcarbamoylmethylphosphine oxide in 30% tri-n-butyl phosphate extraction systems was performed from aqueous solution containing HCl, HNO3 and acetohydroxamic acid. Depending on extraction conditions, acetohydroxamic acid can significantly affect the speciation of molybdenum and can increase or decrease its distribution ratio. Our investigation confirmed the strong ability of the acetohydroxamic acid to form complexes with Mo even in highly acidic solutions. UV absorption spectra confirmed that a fraction of the Mo(VI)-AHA species can be present in the organic phase after extraction.

The Effect of Acetohydroxamic Acid on Extraction and Speciation of Plutonium

Abstract The effect of acetohydroxamic acid (AHA) on speciation of transuranic elements has been investigated in the extraction and spectrophotometric experiments relevant to UREX extraction process. The distribution ratios decreased with increased concentration of added AHA rapidly, and a considerable ability of AHA to form complexes with plutonium even under strong acidic conditions was confirmed. Using FITEQL 4.0, a computer modeling program for equilibrium experimental data, the speciation distribution of tetravalent plutonium was determined. Acetohydroxamate species of Pu(IV) identified in Vis-NIR spectra of the extraction organic phase confirms formation of extractable neutral solvates of ternary acetohydroxamate-nitrate complexes of plutonium with tributyl phosphate (TBP).

The redox chemistry of neptunium in γ-irradiated aqueous nitric acid

Abstract The redox chemistry of neptunium in irradiated 4 M nitric acid was investigated using γ-ray irradiation and UV/Vis spectroscopic measurements. Irradiation caused changes in the abundances of Np(V) and Np(VI) regardless of the initial fractional components of these oxidation states. At low absorbed doses Np(V) was oxidized to Np(VI) in irradiated solution, due to its reaction with oxidizing, radiolytically-produced, free radicals. However, when sufficient radiolytically-produced nitrous acid accumulated, the reduction of Np(VI) to Np(V) occurred, even at this high nitric acid concentration. Neptunium(IV) was not produced. A kinetic model which incorporates the standard water radiolysis reactions, estimated radical yields for 4 M HNO3, and rate constants for neptunium reactions available from the literature was used to successfully reproduce the experimental results.

The Radiolytic and Thermal Stability of Diamides of Dipicolinic Acid

The thermal and radiolytical stabilities of three isomers of N,N′-diethyl-N,N′-ditolyl-dipicolinamide (EtTDPA) were investigated. Radiolysis was performed at doses up to 125 kGy and thermogravimetric analysis was performed at temperatures of up to 450°C. Infrared data showed increasing amounts of aromatic nitration by nitric acid correlating to larger doses. However, gamma ray doses of up to 125 kGy did not cause any significant effects in separation performance with the studied extraction mixtures containing americium or europium within the studied range. The highest separation factor between americium and europium was seen using the meta isomer with an average value of 4.1 across all doses applied in this work.

Spectroscopic Study of the Uranyl–Acetohydroxamate Adduct with Tributyl Phosphate

The ultraviolet–visible (UV-Vis) and Fourier transform infrared (FT-IR) spectroscopic studies carried out for the system UO2(NO3)/AHA/TBP (uranyl–acetohydroxamate–tributyl phosphate) confirmed the presence of the adduct of UO2(NO3)(AHA) ·2TBP with 1:1 stoichiometry for UO2:AHA (acetohydroxamic acid). The spectrum of this complex is identical to the infrared spectrum of the organic phase formed in the uranium distribution experiments with 30% TBP/n-dodecane and AHA present in aqueous phase. Disappearance of the hydroxyl stretching band and a shift in the position of the carbonyl band in the infrared spectra revealed that both the hydroxyl and the carbonyl group of acetohydroxamic acid are involved in the chelate ring with uranium. Also, acetic acid, accrued after acidic hydrolysis of acetohydroxamic acid, was identified in the extraction organic phase.

Complexation Chemistry of Zirconium(IV), Uranium(VI), and Iron(III) with Acetohydroxamic Acid

The complexation of zirconium(IV), uranium(VI), and iron(III) with acetohydroxamic acid (AHA) has been analyzed spectrophotometrically in various ionic strengths at 25°C. Arsenazo III (AAIII) was used as an indicator for unbound zirconium. The SQUAD computational program was employed to evaluate the stability constants. Conditional stability constants of four zirconium complexes Zr(AAIII)3+, , Zr(AHA)3+, and were determined in 1 mol · L−1 HClO4 as log β′ = 5.09, 10.29, 12.78, and 23.13, respectively. Conditional stability constants of UO2(AHA)+, Fe(AHA)2+, , and Fe(AHA)3, in 0.1 mol · L−1 HNO3 were calculated as = 8.32, 11.00, 20.93, and 28.75, respectively.