Speciation of Fe(III) Radionuclides in Aqueous Solutions

Fe(III) radionuclide speciation in aqueous solutions at pH ranging from 1 to 12 and Fe(III) concentration, from 1 ×10^{- 7} to 1 ×10^{- 2} M was studied. At trace Fe(III) concentrations (1 ×10^{- 7} M), the sorption colloids, so-called pseudocolloids, are formed within pH range 3-12. At pH within 0.7-1.5, Fe(III) exists in the form of hydrated cations Fe(H₂O)₆ ^{3 +}, which are hydrolyzed at pH > 1.5 (K _h = 3.7 ×10^{- 3}) to form mononuclear Fe(OH)^{2 +} hydroxo complexes. At Fe(III) concentration exceeding 1 ×10^{- 4} M, Fe₂(OH)5.70.3+ binuclear hydroxo complexes are formed.     

Voltammetric and chronoamperometric studies of silver electrodeposition from a bath containing HEDTA

The electrodeposition of silver on platinum from ammonium-buffered solutions containing HEDTA (N-(2-hydroxyethyl)ethylenediaminetriacetic acid) at various concentrations was investigated. Potentiometric titration and voltammetric studies indicated that in the presence of 2.0 × 10⁻¹ M HEDTA, the deposited silver was reduced from a mixture of [AgHEDTA]²⁻ and [Ag(NH₃)₂]⁺ complexes, whereas at 2.0 × 10⁻² M and 2.0 × 10⁻³ M HEDTA in the electrolyte, the silver was reduced from the [Ag(NH₃)₂]⁺ complexes alone. Hydrodynamic studies showed variation in the diffusion coefficient for the electroactive species in solution, depending on the HEDTA concentration. Chronoamperometric study in a solution containing 2.0 × 10⁻¹ M HEDTA at low overpotential (0.000 V to –0.050 V) showed a transition from progressive to instantaneous nucleation in a single current transient, whereas, at −0.200 V only 3D-progressive nucleation controlled by mass transport was observed. Scanning electron microscope images showed that the silver films produced in silver baths with HEDTA were uniform, without cracks, and fine-grained, regardless of its concentration, while in the absence of HEDTA the morphology was rough and dendritic. X-ray diffraction analysis of the films obtained at various HEDTA concentrations revealed polycrystalline silver, similar to film obtained in cyanide and EDTA/ammonia baths.     

A Quick Method for Recovery of 64xCu from a Deuteron-irradiated Zinc Target

An extraction procedure was developed for quick recovery of carrier-free ⁶⁴Cu from a deuteron-irradiated zinc target, based on extraction of the ionic associate of copper with diantipyrylpropylmethane (R)from iodide-containing sulfuric acid solutions into chloroform. The optimal conditions of the process are asfollows, M: 1 H₂SO₄, 0.1 KI, 2×10^-2-3×10^-2 R. The distribution factor K _d of copper exceeds 10³' whereas for zinc and gallium it is less than 10^-3. The extracted ⁶⁴Cu can be backwashed with a solution ofalkali (NaOH, KOH) or with water. Depending on the backwashing solution (alkali or water), the time of ⁶⁴Cu recovery is 1-1.5 h.     

Oxygen-sensing properties of ormosil hybrid materials doped with ruthenium(II) complexes via a sol-gel process

Organically modified silicate (ormosil) materials doped with [4,4′-dimethyl-2,2′-bipyridine-bis(2,2′-bipyridine)] ruthenium(II) dichloride ([Ru-mbpy]²⁺) and [4,4′-dimethylformate-2,2′-bipyridine-bis(2,2′-bipyridine)] ruthenium(II) dichloride ([Ru-dmfbpy]²⁺) were prepared by a sol-gel procedure for oxygen-sensing applications. The results indicated that the concentrations of the Ru(II) diimine complexes obviously influenced the linearity of Stern-Volmer plots (I₀ /I vs. O₂%). The best suitable concentrations of [Ru-mbpy]²⁺ and [Ru-dmfbpy]²⁺ in the sol for oxygen sensors were found to be 1.0 × 10^− 3 M and 2.5 × 10^− 3 M, respectively. The fluorescence quenching time and recovery time of oxygen sensor doped with [Ru-mbpy]²⁺ (1.0 × 10^− 3 M) were 18 s and 38 s and those doped with [Ru-dmfbpy]²⁺ (1.0 × 10^− 3 M) were 13 s and 32 s, respectively. The oxygen sensor based on Ru(II) complex modified by esterification demonstrated excellent linear calibration relationship and improved long-term stability.     

The reaction Pu(VI) + Fe(CN)<Stack><Subscript>6</Subscript><Superscript>3−</Superscript></Stack> ⇄ Pu(VII) + Fe(CN)<Stack><Subscript>6</Subscript><Superscript>4−</Superscript></Stack> in NaOH solutions

A spectrophotometric study showed that, in 5 M NaOH, Pu(VII) prepared by ozonation of Pu(VI) is reduced with excess K₄Fe(CN)₆. The Pu(VII) content can be estimated from the amount of the Fe(CN)₆³⁻ formed. In NaOH solutions of concentration exceeding 8 M, the Fe(CN)₆³⁻ ion oxidizes Pu(VI). In 10.3 M NaOH, the tenfold excess of K₃Fe(CN)₆ fully converts 1 mM Pu(VI) to the heptavalent state within 4 min (rate constant 1.3 l mol⁻¹ s⁻¹ at 20°C). With an increase in the NaOH concentration, the oxidation rate increases, and smaller excess of K₃Fe(CN)₆ is required. This oxidant is consumed not only for Pu(VI) oxidation but also in reactions with H₂O and OH⁻ ions. Pu(VII) is unstable and is slowly reduced with water and with products of decomposition of iron complexes.     

Solubility of Thorium under Anoxic Conditions

The solubility of thorium was studied in 0.1 M NaCl solution under anoxic carbonate-free conditions. The steady state was approached from both oversaturation and undersaturation. The equilibration periods used ranged up to 71 days. The crystallization of the formed amorphous or microcrystalline solid Th phases was examined by X-ray diffraction. With ICP-MS, the measured Th concentrations in solution were between 10^{- 1 1} and 10^{- 8} M. No indication of Th colloids was detected in the SEM and TEM examinations of the ultrafiltration membrane specimens and the aliquots of solution prepared before and after ultrafiltration. The measured Th concentrations agreed fairly well with the computed values (EQ3/6 code) of Th concentration, about 2 × 10^{- 9} M under CO₂-free conditions.     

Uranyl and Thorium(IV) Sorption from Dilute Nitric Acid Solutions with Dodecavanadic Acid

Sorption of uranyl on dodecavanadic acid proceeds by the ion-exchange mechanism at relatively low metal concentrations in the range (0.8-2.0) ×10^{- 3} M. Sorption of Th(IV) is practically pH-independent over the pH range 1.5-2.5, but depends significantly on the initial Th(IV) concentration. The maximal capacities of DDVA for uranyl and Th(IV) remarkably differ from each other (9 and 6.3 mg-equiv g^{- 1}, respectively). The uranyl compound formed on contacting DDVA with concentrated uranyl nitrate solution was identified by X-ray diffraction as UO₂(VO₃)₂·nH₂O.     

State of Radiorhodium in High-Level Liquid Waste from Regeneration of Spent Nuclear Fuel

The state of radiorhodium in liquid waste from processing of spent nuclear fuel was analyzed in detail by ESR and NMR spectroscopy on several nuclei. The most probable oxidation state of rhodium in nitric acid solutions is +3. Three procedures for preparing nitric acid solutions of rhodium were studied. The composition of Rh(III) complexes in these solutions is similar but not identical. The method for identifying the ionic composition of similar objects was proposed. The speciation of rhodium in nitric acid solutions with the acid concentration ranging from 2×10^{- 2} to 15 M was studied. Polynuclear oligomers with (-ONO₂)₂ bridges, mainly tetramers, are formed in solutions with CRh > 2 M, [NO₃ ^-] 8 M, and [H⁺] 0.7 M. At CRh = (1-2)×10^{- 2}, [NO₃ ^-] = 1-4 M, and [H⁺] = 0.4-4 M, the (-OH, -ONO₂) dimer and trimer prevail; at [NO₃ ^-] < 1 M and [H⁺] < 0.2 M, the (-OH, -ONO₂) dimer dominates. No Rh(III) aqua ion and no monomeric nitrate complexes were detected in the quasiequilibrium system at any concentrations of the components. In nitrate-nitrite solutions, both subnitrated (-OH, -ONO₂) Rh(III) oligomers and mononuclear Rh(III) nitroaqua complexes exist. The equilibrium between these species is attained very slowly and depends on the equilibrium concentration of nitrite anion. Forecast was given on isolation of rhodium from nitric acid solutions of SNF by extraction, ion-exchange, electrolytic, and precipitation procedures.     

AES and XPS study on the tarnishing of silver in alkaline sulphide solutions

Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to follow the changes that occur on the surfaces of silver sheets when reacting with sulphide solutions of pH 12. The results obtained enabled conclusions to be drawn about the nature of the Ag₂S films. Immersion in dilute sulphide solutions ( 3 × 10^–4 M) resulted in highly irregular films that were interrupted by shallow depressions (cavities). Inside these cavities AES analysis proved the existence of massive carbon species, the presence of which delayed healing of the cavities by the formation of Ag₂S film, thus allowing the silver metal interface to continue in contact with the solution oxygen. This explains why silver electrodes maintain the Ag/Ag₂O potential while immersed in dilute sulphide solutions. Equilibration of silver with more concentrated sulphide solutions (5 × 10^–4 to 5 × 10^–3 M) effected healing of the cavities through the formation of a continuous Ag₂S film. Once this continuous film is formed, the metal interface is no longer accessible to the solution oxygen. At this point the transition of potential from Ag/Ag₂O to Ag/Ag₂S occurs.     

Coprecipitation of 60Co from aqueous solutions with triethylenediamine complexes of d-element nitrates

Formation of complexes of Co²⁺ with triethylenediamine (CH₂-CH₂)₃N₂ (Q) in aqueous solution and coprecipitation of microamounts of ⁶⁰Co with triethylenediamine complexes of Cu²⁺, Ni²⁺, and Zn²⁺ nitrates were studied. Microamounts of ⁶⁰Co poorly coprecipitate with triethylenediamine complexes of Cu²⁺ and Zn²⁺ nitrates. At practically 100% precipitation of Cu²⁺ and Zn²⁺ from solutions in the form of the corresponding complexes, the degree of coprecipitation of ⁶⁰Co with these complexes does not exceed 15%. With the Ni²⁺ complexes formed from 10⁻¹ M aqueous solutions at the molar ratios Ni²⁺: Q = 1 : 1 and 1 : 2, the degree of coprecipitation of ⁶⁰Co is about 45 and 90%, respectively.     

Speciation of Cr(III) radionuclides in solutions

The speciation of Cr(III) radionuclides in solutions within the concentration range 10^?6–10^?2 M at pH 1–12 was studied. Adsorption on the glass surface, ion exchange, migration in the electric field, centrifugation, dialysis, and ultrafiltration were used. It was found that, at a concentration of 10^?6 M at pH 1.0–4.4, Cr(III) exists in the solution as a monomeric species, and at pH > 4 it exhibits colloidal properties. At pH 1.0–3.4, Cr(III) exists in form of hydrated cations Cr(H₂O) ₃₊ ⁶ . At pH > 3.4, they are hydrolysed with formation of mononuclear hydroxo complexes Cr(OH)²⁺ [K _h (3.35 ⊥ 0.15) × 10^?5]. At the Cr(III) concentration exceeding 1 × 10^?4 M, binuclear hydroxo complexes Cr₂(OH)_q are formed.     

Interaction of U(VI), Np(VI), and Pu(VI) ions with unsaturated heteropolytungstates of the 17th and 11th series in aqueous solutions

The stability constants of the complexes of U(VI), Np(VI), and Pu(VI) with the heteropolyanions (HPAs) P₂W₁₇O ₆₁ ^10? , SiW₁₁O ₃₉ ^8? , and PW₁₁O ₃₉ ^7? in solutions with pH from ?0.3 (2 M H⁺) to 5–5.5 in the presence of Na or K salts (up to 2 M) and without them were measured. All the complexes have exclusively the 1: 1 composition; their stability constants β^M(VI) in neutral solutions at a low ionic strength are close to 10⁸ 1 mol^?1. In 0.1–2.0 M acid solutions, log β^M(VI) for the complexes with P₂W₁₇O ₆₁ ^10? is within 1.4–3.9. The slope of the pH dependence of log β^M(VI) does not exceed 1.75; this fact suggests that no more than two protons are displaced from HPA upon complexation in acid solutions. In the presence of 1–2 M sodium salts, the β^M(VI) values reach a maximum at pH ～3 and drastically decrease with a further increase in pH. Actinides(VI) interact with HPAs appreciably more weakly than do actinides(III), which is apparently due to the fact that the denticity of HPAs in the complexes with An(VI), apparently, does not exceed 2.     

Redox equilibrium U(VI) + 2Ce(III) ? U(IV) + 2Ce(IV) in the presence of unsaturated heteropoly anions P2W17O 6110? and SiW11O 398?

The equilibrium of the reaction U(VI) + 2Ce(III) ⇄ U(IV) + 2Ce(IV) in the presence of unsalurated heleropoly compounds K₁₀P₂W₁₇O₆₁ and K₈SiW₁₁O₃₉ in 0.01–1.0 M HClO₄ solutions (ionic strength 1) was studied. The potential of the Ce(IV)/Ce(III) couple in K₈SiW₁₁O₃₉ solutions was measured, from which the overall stability constants β₂^IV of the complexes U^IV(SiW₁₁O₃₉)₂¹²⁻, equal to 10^23.8 and 10^19.8 in 0.1 M HClO₄ + 0.9 M NaClO₄ and in 1.0 M HClO₄, respectively, were calculated. Under the same conditions, for the complex U^IV(P₂W₁₇O₆₁)₂¹⁶⁻ β₂^IV = 10^23.2 and 10^18.5 (the latter value was obtained by extrapolation or data for 0.1 M HClO₄ + 0.9 M NaClO₄ solution). Original Russian Text ? V.P. Shilov. A.B. Yusov, M.N. Sokohva. A.M. Fedoseev, 2008, published in Radiokhimiya, 2008, Vol. 50. No. 3, pp. 203–208.     

Polyvinylpyrrolidone macromolecules function as a diffusion barrier during dealloying

The inhibition effect of polyvinylprrolidone (PVP) during dealloying on the formation of nanoporous Cu from a Ti₆₀Cu₄₀ amorphous alloy in hydrofluoric acids (HF) was investigated. A bicontinuous nanoporous Cu structure formed on Ti₆₀Cu₄₀ after dealloying. The pore size of nanoporous Cu formed in HF solution was 71 nm, but this decreased to 12 nm and 11 nm after dealloying for the same period of dealloying time of 43.2 ks when 0.01 M and 0.03 M PVP, respectively, was added into the 0.03 M HF base solution. The surface diffusivity was estimated to decrease from 2.5 × 10⁻¹⁸ m² s⁻¹ in 0.03 M HF solution to 1.84 × 10⁻²¹ m² s⁻¹ when 0.01 M PVP was added, and to 1.42 × 10⁻²¹ m² s⁻¹ when 0.03 M PVP was added. More PVP macromolecules were adsorbed onto the nanoporous Cu surface in the 0.03 M HF solution with the addition of 0.03 M PVP than when 0.01 M PVP was added to the solution, which resulted in the formation of smaller nanopores. The suppressed diffusion of Cu adatoms due to the PVP macromolecule resulted in the formation of finer Cu ligaments than that formed in 0.03 M HF solution. This long chain organic molecule was shown to act as a diffusion barrier for the diffusion of metal adatoms during dealloying and to elaborate the nanoporous structure.     

Optical and structural properties of chemically deposited CdS thin films on polyethylene naphthalate substrates

CdS thin films were deposited on polyethylene naphthalate substrates by means of the chemical bath deposition technique in an ammonia-free cadmium-sodium citrate system. Three sets of CdS films were grown in precursor solutions with different contents of Cd and thiourea maintaining constant the concentration ratios [Cd]/[thiourea] and [Cd]/[sodium citrate] at 0.2 and 0.1 M/M, respectively. The concentrations of cadmium in the reaction solutions were 0.01, 7.5 × 10⁻³ and 6.8 × 10⁻³ M, respectively. The three sets of CdS films were homogeneous, hard, specularly reflecting, yellowish and adhered very well to the plastic substrates, quite similar to those deposited on glass substrates. The structural and optical properties of the CdS films were determined from X-ray diffraction, optical transmission and reflection spectroscopy and atomic force microscopy measurements. We found that the properties of the films depend on both the amount of Cd in the growth solutions and on the deposition time. The increasing of Cd concentration in the reaction solution yield to thicker CdS films with smaller grain size, shorter lattice constant, and higher energy band gap. The energy band gap of the CdS films varied in the range 2.42-2.54 eV depending on the precursor solution. The properties of the films were analyzed in terms of the growth mechanisms during the chemical deposition of CdS layers.     

Effect of salts on oxidation of Np(VI) with Fe(CN)<Stack><Subscript>6</Subscript><Superscript>3−</Superscript></Stack> Ions in 0.1–1 M alkali solutions

The potential of the Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ couple in solutions containing 0.5–1 M alkali and high concentrations of Li, Na, and K salts was estimated potentiometrically. The reactions of Fe(CN)₆³⁻ with Np(VI) in such media were studied by spectrophotometry. In 0.5–1 M KOH + 7 M KF or 0.5–1 M KOH + 8 solutions, Np(VI) is oxidized to the heptavalent state with a small excess of Fe(CN)₆³⁻. In the presence of lithium or sodium salts, a larger excess of the oxidant is required for complete oxidation of Np(VI). Carbonate ions in concentrations exceeding 2 M prevent the Np(VI) oxidation.     

Transport properties and thermal expansion of La2Mo2O9-based solid electrolytes

The oxygen ion transference numbers of La_1.7Bi_0.3Mo₂O₉, La₂Mo_1.7W_0.3O₉ and La₂Mo_1.95V_0.05O₉ ceramics, determined by modified faradaic efficiency and e.m.f. methods at 973-1173 K, vary in the range 0.995-0.977 in air, decreasing when temperature increases. The activation energies for the ionic and electronic transport are 61-71 kJ/mol and 123-141 kJ/mol, respectively. Reducing oxygen chemical potential leads to increasing n-type electronic contribution to the total conductivity, which remains, however, essentially p(O₂)-independent down to oxygen pressures of 10⁻⁴-10⁻³ atm and exhibits reversible drop on further reduction, probably due to phase decomposition. Doping La₂Mo₂O₉ with calcium results in segregation of a CaMoO₄-based phase, accompanied with increasing electronic transport. The average thermal expansion coefficients of La₂Mo₂O₉-based materials, calculated from dilatometric data in air, are (14.4-14.8) × 10⁻⁶ K⁻¹ at 300-700 K and (16.4-22.5) × 10⁻⁶ K⁻¹ at 700-1070 K.     

Modified carbon paste electrode for potentiometric determination of diquat dibromide pesticide in water and urine samples

A carbon paste electrode for diquat dibromide (Dq.2Br) was prepared and fully characterized in terms of composition, usable pH range, response time and temperature. The electrode was applied to the potentiometric determination of diquat ions in water and urine samples with average recoveries of 97.5-104.0% and relative standard deviations of 0.30-4.73%. The electrode is based on the ion pair, namely, diquat-phosphotungstate dissolved in 2-nitrophenyloctyl ether (2-NPOE) as pasting liquid with 1.0% Na-TPB as an additive. The modified electrode showed a near-Nernstian slope of 30.8 mV over the concentration range of 3.8 × 10^− 6to 1.0 × 10^− 3 M with the limit of detection 9.0 × 10^− 7 over the pH range 4.5-9.5. The electrode exhibits good selectivity for Dq cations with respect to a large number of inorganic cations, organic cations, sugars and amino acids. The proposed potentiometric method offers the advantages of simplicity, accuracy, automation feasibility and applicability to turbid and colored sample solutions.     

Investigation of precursors concentration in spray solution on the optoelectronic properties of CuInSe2 thin films deposited by spray pyrolysis method

Copper indium selenide CuInSe₂(CISe) thin films were deposited by chemical spray pyrolysis (CSP) method of CuInS₂(CIS) and subsequent selenization process. To study the effects of solution concentration, we prepared different precursors solution of CIS including different amount of indium salts from 0.025 to 0.100 M with In/Cu 1.25 and S/In 4. These results propose that solution concentration is critical for inflecting the morphological, optical, electrical, and electrochemical characteristics of solution-processed CISe films and device performance. The studied morphological properties of deposited samples were homogenous, crack-free with large grains in indium salt concentrations more than 0.075 M. The deposited film thickness depends on the spray precursor concentration and increases for higher concentration. In addition with increasing of indium precursor concentration from 0.025 to 0.100 M in spray solution, the optical bandgap of deposited film decreases from 1.40 to 1.35 eV. Also the films mobility and carrier density were notably influenced by any change in the solution concentration. Electrical and electrochemical properties showed a decrease in carrier density from?~?10²⁰ to?~?10¹⁷ cm^?3 and the increase in mobility of order?~?10^–7 to?~?10^–2 cm²/V s, respectively, for 0.025 M, 0.100 M CISe films. All films exhibited p-type conductivity owing to different concentrations. However, it seems that the concentration of the ideal solution is 0.100 molars.

     

Coprecipitation of Trace Amounts of <Superscript>137</Superscript>Cs and <Superscript>85</Superscript>Sr with [Na(18-Crown-6]BPh<Subscript>4</Subscript> from Neutral and Alkaline Solutions

Coprecipitation of ¹³⁷Cs and ⁸⁵Sr with [Na(18-crown-6]BPh₄ solid phase from aqueous, aqueous-ethanolic, and alkaline solutions is studied. ¹³⁷Cs and ⁸⁵Sr cocrystallize with [Na(18-crown-6]BPh₄ from aqueous and aqueous-ethanolic solutions. The cocrystallization coefficients D of ¹³⁷Cs and ⁸⁵Sr from aqueous solutions are 2.6±0.5 and 3.3±0.3, respectively. For aqueous-ethanolic solutions, the corresponding values are 4.4±0.5 and 3.4±0.4. In the alkaline solutions (0.1 and 1 M NaOH), 54–74% of ¹³⁷Cs and 37–51% of ⁸⁵Sr pass into the [Na(18-crown-6]BPh₄ solid phase, depending on the crown ether concentration in the system.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 257–260.Original Russian Text Copyright © 2005 by Kulyukhin, Konovalova, Rumer, Kamenskaya, Mikheev.