Interaction of Aluminum with Am(III) and Certain REE(III) Ions in Alkaline Solutions

Precipitates prepared by addition of ammonia or NaOH into solutions containing Al and REE(III) (La, Nd) or Al and Am(III) were studied by thermogravimetry, UV-Vis and IR spectroscopy, X-ray diffraction analysis, and measurement of the dissolution rate. It was shown that the properties of the precipitates containing Al and the second element noticeably differ from the properties of straight aluminum hydroxide precipitate. In the IR spectra, new vibrational bands appear. In the electronic spectra, small shifts of Nd(III) and Am(III) absorption bands relative to the bands of the individual f-element hydroxides are observed. The rates of dissolution of the precipitates in HCl solutions noticeably differ. With increasing pH of coagulation to 13-14, a part of aluminum is captured with the precipitate. However, this fraction is small. In the precipitates obtained from 0.1-1 M NaOH, the interaction of f elements with aluminum is practically lacking.     

Redox Behavior of Am(IV) and Methods of Its Preparation in Alkaline Media

A scheme was suggested for Am(OH)₄ isolation by treatment of Am(OH)₃ suspension in 0.1–1.0 M NaOH with ozone (3.5–5 vol %)-oxygen mixture (4–5 l h⁻¹ flow rate) at 20°C for 40 min, followed by ultrasonic treatment of the resulting Am(VI) (44 kHz, 1 W cm⁻³) for 45 min. The separated precipitate of Am(III) hydroxy peroxide was treated with 1–2 mlof 7–10 M NaOH to form Am(OH)₄. Mixing suspensions of equivalent amounts of Am(III) and Am(V) hydroxides in NaOH also gives Am(IV) hydroxide in a >98% yield. The reproportionation Am(III) + Am(V) = 2Am(IV) in 1 M NaOH starts on heating above 70°C, whereas at NaOH concentration higher than 7 M it is completed even at room temperature. The reaction of Am(III) with Am(VI) in alkaline solutions, Am(VI) + 2Am(III) → 3Am(IV), occurs during mixing the reactants. The equilibrium reaction of Am(OH)3 with [Fe(CN)₆]³⁻ in alkaline solutions was studied. It was shown that increasing the alkali concentration to 2 M NaOH promotes formation of Am(OH)₄. At further increase in the alkali concentration, Am(V) is formed.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 234–238.Original Russian Text Copyright © 2005 by Nikonov, Gogolev, Tananaev, Myasoedov, Clark.     

Influence of temperature on phase separation in the binary system tetradecane-Nd(III) nitrate solvate with tri-n-butyl phosphate and ternary system tetradecane-tri-n-butyl phosphate-Nd(III) nitrate solvate with tri-n-butyl phosphate

The phase diagrams of the liquid binary system tetradecane-Nd(III) nitrate solvate with tri-n-butyl phosphate [Nd(NO₃)₃ (TBP)₃] and ternary liquid system tetradecane-tri-n-butyl phosphate-Nd(III) nitrate solvate with tri-n-butyl phosphate were studied in the temperature range 298.15–344.85 K. The phase diagrams of the binary and ternary systems contain an area of homogeneous solutions and an area of separation into two liquid phases (I, II). Phases I and II are enriched in tetradecane and Nd(NO₃)₃ (TBP)₃, respectively. With increasing temperature, the areas of separation into two liquid phases in the binary and ternary systems contract. The compositions of the binary and ternary systems in the critical points at different temperatures and their upper critical solution temperatures were determined.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 433–435.Original Russian Text Copyright © 2004 by Pyartman, Kudrova, Keskinov.     

Extraction of Lanthanide(III) Nitrates from Aqueous Solutions with Mixtures n-Octanol-Decane, Tri-n-butyl Phosphate-n-Octanol, and Diisoamyl Methylphosphonate-n-Octanol

Extraction of lanthanide(III) (La-Eu) nitrates from aqueous solutions with 3.15 M solution of octanol (ROH) in n-decane (extractant 1), 2.02 M solution of diisoamyl methylphosphonate (S = DIAMP) in n-octanol (extractant 2), and 1.83 M solution of tri-n-butyl phosphate (S = TBP) in n-octanol (extractant 3) was studied at T = 298.15 K. The extraction of lanthanide(III) nitrates with extractant 1 at C(aq) > 0.6 M is described by the equation of the heterogeneous reaction Ln³⁺(aq) + 3NO ₃ ⁻ (aq) + 4ROH(o) = [Ln(NO₃)₃ ⋅ (ROH)₄](o). The extraction of Ln(III) nitrates with extractants 2 and 3 involves the reaction described above in combination with the heterogeneous reaction Ln³⁺(aq) + 3NO ₃ ⁻ (aq) + 3S(o) = [Ln(NO₃)₃(S)₃](o) and the homogeneous reaction ROH(o) + S(o) = [ROH ⋅ S](o), where S is DIAMP or TBP. The electronic absorption and IR spectra of Nd(III) and Pr(III) nitrates in n-octanol and n-octanol-TBP mixtures were analyzed.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 245–251.Original Russian Text Copyright © 2005 by Kudrova, Keskinov, Pyartman.     

Dissolution of WWER-1000 spent nuclear fuel in a weakly acidic solution of iron nitrate and recovery of actinides and rare earth elements with TBP solutions

It is demonstrated on real solutions of samples of spent nuclear fuel (SNF) from WWER-1000 reactors (1000-MW_el water-cooled water-moderated energy reactors) that weakly acidic solutions of iron(III) nitrate at the molar ratio Fe(III): U ≥ 2.0 dissolve SNF with quantitative transfer of U and Pu into the solution. In the process, Fe partially precipitates in the form of a basic salt precipitate together with a part of the fission products (>90% of Ru, ~90% of Мо, >60% of Tc, and 40% of Zr) already in the step of the fuel dissolution. Cs, Eu, and Am pass into the solution together with U and Pu. With the required conditions followed, U and Pu can be separated from the solution by precipitation of their peroxides or quantitatively extracted from this solution with 30% TBP in Isopar L. The presence of ≥1 M Fe(NO₃)₃ in the solution considerably increases the distribution ratios of TPE and REE, which allows their recovery from a weakly acidic nitrate solution to be also performed with 30% TBP in a diluent. This process can serve in the future as a basis for the development of a new integrated technology combining the PUREX process with TPE partitioning using a common extractant.     

Neodymium(III)-PVC membrane sensor based on a new four dentate ionophore

A new selective Nd(III) sensor has been made by using N,N′-bis(quinoline-2-carboxamido)-4,5-dimethylbenzene (H₂L₄) as a suitable ionophore. The sensor exhibits Nernstian response to Nd(III) ions in the concentration range of 5.0 × 10^− 6 to 1.0 × 10^− 2 M. It displays a Nernstian slope of 19.5 ± 0.4 mV/decade in the pH range of 2.9-9.2. The proposed sensor also exhibits a fast response time of < l0 s. The detection limit of the proposed sensor is 4.8 × 10^− 6 M, and it can be used over a period of 10 weeks without significant changes in its response. Furthermore, the electrode showed high selectivity toward Nd(III) ion respect to all other lanthanide ions tested. The practical utility of the sensor was demonstrated by using it as an indicator electrode in the potentiometric determination of Nd(III) ions in certified reference material and spiked water samples.     

Improvement of the magnetic and electric properties of Cu-Zn ferrites

We study Cu-Zn polycrystalline ferrites substituted with rare-earth ions. For substituted samples (R = Nd, Sm, and Gd), the initial magnetic permeability and homogeneity increase as compared with nonsubstituted samples. At the same time, the magnetization and energy losses decrease for all substituted samples. The specific resistance increases only for samples with R = La and Nd. The grain sizes increase for all substituted samples (as compared with nonsubstituted) except the samples with R = La and Nd. It is shown that the Curie temperature is almost constant and does not depend on the type of substituted rare-earth ions.Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 4, pp. 84–88, July–August, 2004.     

Use of ozone for dissolving high-level plutonium dioxide in nitric acid in the presence of Am(V,VI) ions

Plutonium dioxide recovered in the course of reprocessing of SNF from WWER reactors (so-called high-level PuO₂) was subjected to dissolution in 0.6–3.0 M HNO₃ in the presence of Am(III) ions under ozonation with an ozone-oxygen mixture containing 30–180 mg l⁻¹ O₃. Measurements of the rate of the PuO₂ dissolution in 3 M HNO₃ in the temperature interval from 30 to 80°C showed that, with an increase in the ozone concentration in the ozone-oxygen mixture from 30 to 180 mg l⁻¹, the dissolution rate increases by a factor of 4–5. The acceleration of the PuO₂ dissolution is attributed to the formation of Am(V,VI) by homogeneous oxidation of Am(III) ions with ozone dissolved in HNO₃. The Am dioxocations formed act as PuO₂ oxidants and are continuously regenerated by the oxidation of Am(III) with ozone. This assumption is confirmed by an additional increase in the dissolution rate, observed on introducing Am(III) into the initial electrolyte for the PuO₂ dissolution.     

Incorporation of bismuth into Ba6− x R8+2/3x Ti18O54(R = Nd, Gd)

Microstructural investigations and microanalyses of a series of Ba_6–x R _8+2/3x Ti₁₈O₅₄ ceramics (R = Nd, Gd) revealed that the solid-solubility limit for the isovalent substitution of R ³⁺ by Bi³⁺ depends on the composition of the Ba_6–x R _8+2/3x Ti₁₈O₅₄ phase. For the Nd analogue the solid-solubility limit (y in Ba_6–x (Nd_1–y Bi _y )_8+2/3x Ti₁₈O₅₄) decreases with a decrease in x from y = 0.16 for x = 2.0 to y = 0.10 for x = 0.8. An even lower solid-solubility limit (y = 0.06) was found for the Ba_4.5(Gd_1–y Bi _y )₉Ti₁₈O₅₄ compound (x = 1.5). All substituted Nd compositions exhibit higher permittivities (93–99), lower temperature coefficients of permittivity (11–15 ppm/K) and higher dielectric losses (Q · f = 1300–5500 GHz) than the parent compositions. By exceeding the solid-solubility limit, abrupt changes in the microstructural and dielectric characteristics are induced.     

Reduction of Am(IV) with Water in KHCO3 + K2CO3 Solutions

Reduction of Am(IV) with water in KHCO₃, K₂CO₃ solutions (pH 8.5-10.5) was studiedspectrophotometrically at 54-70°C. The Am(IV) concentration decreases, following the first-order rate law.The reduction rate increases with pH (logk/pH = 0.4), but decreases with increase in (HCO₃ ^- + CO₃ ^{2 -}) concentration. It was assumed that the thermally excited Am(IV) ion forms a dimer with unexcited Am(IV). The dimer dissociates into two Am(III) ions and H₂O₂. Hydrogen peroxide reduces two more Am(IV) ions. In this process, the excited Am(III) ion appears, which transfers the excitation to Am(IV) at collision. Thus, a chain process is initiated. This scheme can also explain the kinetics of Am(VI) and Np(VII) reduction in carbonate solutions.     

Growth of fibrous hydroxyapatite in the gel system

Hydroxyapatite (HAP) was prepared in the agar gel system, where Ca²⁺ ions were incorporated in the gel and PO ₄ ^3– solution was layered over the gel. When the concentration of Ca²⁺ was lower than 1.0 M and the initial solution Ca/P molar ratio was lower than about unity, fibrous HAP several centimetres to several tens of centimetres in length was grown upwards in the PO ₄ ^3– solution from the gel phase, while at the larger Ca²⁺ concentration and initial Ca/P molar ratio CaHPO₄ · 2H₂O (DCPD) in the form of gelatinous precipitate, particulate precipitates or needle-like crystals were preferred to HAP. The fibrous HAP was calcium deficient and composed of small elongated hollow ovals linked in a zigzag row. This was considered to be formed in the following manner. First, Ca²⁺ ions supplied through pores in the gel reacted with PO ₄ ^3– ions to form a small spherulite at the pore exit, then the spherulite was bloated and elongated by the osmotic pressure or capillary force until a part of the oval was broken for Ca²⁺ ions to be gushed out into the PO ₄ ^3– solution. The above two processes were repeated to form elongated hollow ovals linked to the preceding ones.     

Mechanism of Am(III) oxidation with ozone in carbonate solutions

The reaction of ozone with Am(III) in bicarbonate and carbonate solutions was studied by spectrophotometry. On adding ozone-saturated water to a 2 × 10⁻⁴ M Am(III) solution in 1 M NaHCO₃, about 1/3 of Am remains in the trivalent state and 2/3 is converted to Am(V), with no accumulation of Am(IV). The reaction of Am(III) with ozone involves replacement of H₂O molecules in the coordination sphere of Am(III) by O₃ molecule, followed by elimination of the O₂ molecule. The third O atom remains bonded with Am, converting it to the pentavalent state.     

N2O decomposition over (Mg6−xAx) MnO8 (A = Li, Al)

Two different murdochite-type mixed oxides, (Mg_6–x Li _x )MnO₈ (x = 0, 0.1, 0.2 and 0.3) and (Mg_6–x Al _x )MnO₈ (x = 0, 0.2, 0.4, 0.6) were examined for the catalytic decomposition of N₂O in order to make clear the effects of mixed valencies of pairing manganese ions and oxygen vacancies. The valence of manganese ions and the amount of surface oxygen vacancies have been examined with X-ray photoelectron spectroscopy (XPS). (Mg_6–x Li _x )MnO₈ had mixed valence manganese ions and oxygen vacancies on the surface after the substitution. The substituted (Mg_6–x Al _x )MnO₈ had a mixed valence state but oxygen vacancies decresed with x and excess oxygen over stoichiometry was observed at x = 0.4 and 0.6. The reaction rate of N₂O decomposition increased after substitution with lithium but hardly increased after the substitution with aluminum in (Mg_6–x A _x )MnO₈. We assumed that the presence of oxygen vacancies on the surface along with pairing altervalent manganese ions affected strongly to enhance the reactivity of N₂O decomposition.     

Composition and Properties of Crystals Growing in the Ca2+–Mg2+–HPO2- 4–HCO- 3 System in the Presence of Na+, K+, Cl–, and SO2- 4 Ions

Data are presented on crystallization processes in aqueous solutions in the Ca²⁺–Mg²⁺–HPO^2- ₄–HCO^- ₃ system in the presence of Na⁺, K⁺, Cl^–, and SO^2- ₄ ions for molar ratios of the ions similar to those in human blood plasma. The solution concentration is shown to have a significant effect on the chemical composition and physicochemical properties of the forming precipitates.     

Magneto-optical activity of f–f transitions in elpasolite Rb2NaDyF6

Absorption and magnetic circular dichroism (MCD) spectra of f–f transitions ⁶H_15/2 → ⁶F_3/2, ⁶F_5/2, ⁶(F_7/2 + H_5/2) have been measured in cubic crystal Rb₂NaDyF₆ with Dy³⁺ ions in centrosymmetrical O_h positions. Magneto-optical activities (MOA) of the transitions (the ratio of zero moments of the MCD and absorption bands) have been obtained from the corresponding spectra. Origins of the transitions MOA have been analyzed and theoretical estimations of the MOA values have been made. It turned out, that MOA of the transitions in the centrosymmetrical crystal Rb₂NaDyF₆ (being allowed by odd vibrations) are noticeably larger than those in non-centrosymmetrical compounds, where f–f transitions are allowed by static odd components of crystal field.     

Extraction of U(VI), Th(IV), Pu(IV), Am(III), and rare-earth elements from nitric acid solutions with diphenyl(dialkylcarbamoylmethyl)phosphine oxides substituted in the methylene bridge

The extractive power and selectivity of diphenyl(dialkylcarbamoylmethyl)phosphine oxides in extraction of U(VI), Th(IV), Pu(IV), Am(III), and rare-earth elements from nitric acid solutions was studied, as influenced by substitution of one or two hydrogen atoms in the methylene bridge with alkyl, cycloalkyl, CH₂P(O)Ph₂, and CH₂C(O)NBu₂ groups.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 427–432.Original Russian Text Copyright © 2004 by Turanov, Karandashev, Yarkevich, Safronova, Kharitonov, Radygina, Fedoseev.     

Preparation and properties of Mn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> M<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se (M = Ti,V, Fe,Co) solid solutions

Mn_{1 – x} M_x Se (M = Ti, V, Fe, Co) solid solutions are prepared by solid-state reactions and high-pressure synthesis (7 GPa, 1600 K). All of the solid solutions have a cubic (NaCl) structure, and their lattice parameter decreases with increasing solute concentration. The magnetic susceptibility of the solid solutions is measured from 77 to 900 K by the Faraday method. Below 130–150 K, the solid solutions undergo antiferromagnetic ordering.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1431–1434.Original Russian Text Copyright © 2004 by Makovetskii, Galyas, Demidenko     

Extraction of f Elements and Technetium from HNO3 Solutions with Solutions of Alkyl (N,N-Diethylcarbamoylmethyl)phenylphosphinates

Phosphinic acid derivatives, alkyl (N,N-diethylcarbamoylmethyl)phenylphosphinates (ADPs) were synthesized, studied, and tested as extractants for f elements and technetium at the Mayak Production Association. The distribution factors of these elements D were studied in relation to the ADP and HNO₃ concentrations. The influence exerted by the structure of the alkoxy group at the P atom on DAm and DEu in extraction of Am(III) and Eu(III) (chosen as examples) from nitric acid solutions with solutions of ADPs in dichloroethane was examined. The differences between the distribution factors of Am(III), Pu(IV), U(VI), and Tc(VII) are sufficiently high for complete separation of these elements with a high degree of purification in one step of extraction with ADP solutions. The changes observed in the IR spectrum of the 2-ethylhexyl ADP upon complexation with Pr(III) suggest high complexing power of this reagent toward lanthanide ions. The spectrometric data suggest bidentate coordination of the metal with the chelating groups of the reagent.     

Structural and dielectric properties of solid solutions of sodium niobate in lanthanum and neodymium niobates

Experimental evidence is presented for the formation of continuous series of Ln_{2/3 – x}Na_{3x4/3 – 2x}Nb₂O₆ (Ln = La, Nd) perovskite-like solid solutions. Increasing the Na content of the solid solutions reduces their symmetry from Pmmm to Pmmn and then to Pbcm. The structural and dielectric properties of the solid solutions belonging to the three space groups are studied.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1508–1514.Original Russian Text Copyright © 2004 by Mishchuk, Vyunov, Ovchar, Belous.