A Spectrophotometric Study of the Interaction of Uranyl Ions with Orthosilicic Acid and Polymeric Silicic Acids in Aqueous Solutions

The interaction of UO ₂ ²⁺ ions with orthosilicic acid Si(OH)₄ and polymeric silicic acids (PSAs) was studied spectrophotometrically. The equilibrium constant of the reaction UO ₂ ²⁺ + Si(OH)₄ = UO₂OSi(OH) ₃ ⁺ + H⁺ in solutions with the ionic strength I = 0.1–0.2 is log K = −2.56±0.09 (log K ⁰ = −2.29±0.09 recalculated to I = 0); the stability constant of the complex UO₂OSi(OH) ₃ ⁺ (I = 0) is log β⁰ = 7.52±0.09. Formation of small oligomers (degree of polymerization n ≤ 4) has virtually no effect on the apparent constant K. When high polymers are formed (n > 100), the apparent equilibrium constant decreases by a factor of 2–3, and the “true” equilibrium constant recalculated to the actual concentration of silanol groups increases by a factor of 3–4. The absorption spectrum of the complex UO₂OSi(OH) ₃ ⁺ was obtained by treatment of the experimental spectra; it has an absorption maximum in the visible range at 422.5 nm, ɛ_422.5 = 35±2 l mol⁻¹ cm^{− 1}. At pH higher than 5–6, complexes of UO ₂ ²⁺ with PSAs of the composition UO₂(≡SiO)₂(≡ SiOH) _{m − 2} are formed. The absorption spectrum of such a complex was obtained.__________Translated from Radiokhimiya, Vol. 47, No. 4, 2005, pp. 315–321.Original Russian Text Copyright © 2005 by Yusov, Fedoseev.     

Reduction of Np(VI) with Hexamethylenetetraacetic Acid in HClO4 Solution

Radiochemistry - Spectroscopic method was used to examine the stoichiometry of the reaction of No(VI) with hexamethylenediaminetetraacetic acid (HMDTA, H4hmdta) in a 0.05 M HClO4 solution. At an...     

Reaction of Np(VI) with nitrilotriacetic acid in perchloric acid solutions

Stoichiometry of the reaction of Np(VI) with N(CH₂COOH)₃ (NTA) in a 0.05 M HClO₄ solution was studied by spectrophotometry. With excess Np(VI), 1 mol of NTA reduces 2 mol of Np(VI) to Np(V). In 0.05–0.98 M HClO4 solutions (the ionic strength I = 1.0 was maintained by adding LiClO4) containing 5–30 mmol of NTA, at 25–45°С Np(VI) at a concentration of 0.3–2 mM is consumed in accordance with a firstorder rate law until less than 1/3 of Np(VI) remains in the solution. After that, the reaction decelerates. The reaction is first-order with respect to NTA and has an order of–2 with respect to Н⁺ ions. The activated complex is formed with the loss of two Н⁺ ions. The activation energy of the reaction is 100 ± 2 kJ mol^–1.     

Reaction of Np(VI) with <Emphasis Type="Italic">N</Emphasis>-(2-Hydroxyethyl)ethylenediaminetriacetic acid in perchloric acid solutions

The stoichiometry of the reaction Np(VI) + H₃hedta [hedta is N-(2-hydroxyethyl)ethylenediaminetriacetate, HEDTA, anion] in a 0.05 M HClO₄ solution was studied by spectrophotometry. With Np(VI) in excess, 1 mol of HEDTA reduces 4 mol of Np(VI) to Np(V). In 0.125–1.0 M HClO₄ solutions (the ionic strength of 1.0 was maintained constant by adding LiClO₄), containing 3–29.2 mM HEDTA, at 20–45°С Np(VI) at a concentration of 0.4–3.5 mM is consumed in accordance with a first-order rate law until approximately 40% of Np(VI) remains. Then, the reaction decelerates. The reaction rate has first order with respect to [HEDTA] and the order of–1.6 with respect to [Н⁺]. The activated complex arises with the loss of one and two Н⁺ ions. The activation energy is 88.4 ± 5.3 kJ mol^–1.     

Reaction of Np(VI) with cyclohexanediaminetetraacetic acid in HClO<Subscript>4</Subscript> solutions

The stoichiometry of the reaction of Np(VI) with cis-cyclohexanediaminetetraacetic acid (CHDTA, H4chdta) in 0.05 M HClO₄ solution was studied by spectrophotometry. With Np(VI) in excess, 1 mol of the complexone converts 4 mol of Np(VI) into Np(V). In 0.115–0.98 M HClO₄ solutions (the ionic strength of 1.0 was supported with LiClO₄) containing 3–29 mM CHDTA at 20–45°С, Np(VI) at a concentration of 0.2–3.3 mM is consumed in accordance with the first-order rate law until less than 40% of Np(VI) remains. After that, the reaction decelerates. The reaction rate has first order with respect to [CHDTA] and the order of–1.2 with respect to [H⁺]. The activated complex is formed with the loss of one and two Н⁺ ions. The activation energy is 82.3 ± 3.8 kJ mol^–1.     

Complexes of Np(VI) with Cyclobutanecarboxylic Acid Anions and Single-Charged Cations in the Outer Sphere: [NH4][NpO2(cbc)3], [C(NH2)3][NpO2(cbc)3], and [N(CH3)4][NpO2(cbc)3]

Radiochemistry - Three new Np(VI) complexes with cyclobutanecarboxylic acid anions and single-charged outer-sphere anions: ammonium, [NH4][NpO2(cbc)3] (I), guanidinium, [C(NH2)3][NpO2(cbc)3] (II),...     

The improved resonator method for measuring the complex permittivity of materials

An improved resonator method for determination of the complex permittivity of materials in a reflective resonator is presented. The method is specific in the following. In the obtained relationship, imaginary part ε₂ of the permittivity of an investigated material is determined using the variation of the resonance frequency and coupling coefficient of the resonator observed when a specimen is introduced, which increases the measurement accuracy. The method is approbated in the investigations of high-resistance silicon specimens.     

Extraction of U(VI), Th(IV), Pu(IV), and Am(III) from nitric acid solutions with polyfunctional organophosphorus acids

Extraction of microamounts of U(VI), Th(IV), Pu(IV), and Am(III) nitrates from aqueous HNO₃ solutions with solutions of (diphenylphosphinylmethyl)phenylphosphinic, (di-p-tolylphosphinylmethyl)phenylphosphinic, and (dioctylphosphinylmethyl)phosphinic acids and of butyl hydrogen (diphenylphosphinylmethyl)phosphonate in organic diluents was studied. The metal: extractant stoichiometric ratio in the extractable complexes was determined, and the diluent effect on the extraction efficiency was examined. The possibility of using a macroporous polymeric sorbent impregnated with (dioctylphosphinylmethyl)phenylphosphinic acid for concentrating metal ions from HNO₃ solutions was demonstrated.     

Disproportionation of nonoxygenated U(V) bound in the complex with heteropoly anions P<Subscript>2</Subscript>W<Subscript>17</Subscript>O<Stack><Subscript>61</Subscript><Superscript>10−</Superscript></Stack>

The effect of experimental conditions on U^VL₂ (1–2 mM) disproportionation was studied spectrophotometrically through the U^IVL₂ accumulation (L = P₂W₁₇O ₆₁ ^10? ). In 1 M NaNO₃ solution containing 0.01 M HAc and 0.01 M NaAc, the rate of U^VL₂ disappearance is described by the equation V = k ₁[U^VL₂]. The k ₁ value is almost constant with pH decreasing from 4.5 to 1.7, but increases with increasing acetate concentration; the presence of 1 mM U^IVL₂, U(VI), or L does not affect k ₁. In the solutions of 0.1–1.0 M HClO₄ (ionic strength 1), the reaction rate is described by the equation V = 2k ₂[H⁺]^2.5[U^VL₂]². Probable disproportionation mechanism is discussed. The first stage is substitution of L by water molecules in the U^IVL₂ complex and appearance of the reactive U(V) complex with mixed coordination sphere.