Adsorption and desorption of Am(III) on calcareous soil and its parent material

Summary The adsorption and desorption of Am(III) on a calcareous soil (sierozem) and its parent material (loess) were studied by batch technique. The molarities of the Am(III) aqueous solutions were less than 5 ^. 10^-9 mol/l. High adsorbability was found of Am(III) on the calcareous soil and its parent material. In order to decrease the adsorption and, hence, to investigate the adsorption characteristics properly, stable Eu³⁺ as hold back carrier and analogue was added to the aqueous solution. The relative contributions of CaCO₃, organic matter (OM) to the Am(III) adsorption on calcareous soil and its parent material were investigated. The adsorption and desorption isotherms of Am(III) on untreated soil and loess and the three kinds of treated soils and three kinds of treated loesses to remove CaCO₃, OM and both CaCO₃ and OM were determined, respectively. It was found that all isotherms were linear, the average distribution coefficients (K^-_d) for the untreated soil and for the untreated loess were almost equal, while there was an obvious difference between the values of the average distribution coefficients (K^-_d) for the treated soil and the treated loess to remove CaCO₃ or OM. The adsorption-desorption hysteresis on the untreated and treated soils and loesses actually occurred and there was an obvious difference between the hysteresis coefficients on both the corresponding treated soil and loess. It can be concluded that the adsorbability of Am(III) on calcareous soil is similar to that on its parent material, and that the contributions of CaCO₃ and OM to the Am(III) adsorption by the untreated soil are different from those by the untreated parent material.     

Interaction of neptunyl with goethite (α-FeOOH), maghemite (γ-Fe2O3), and hematite (α-Fe2O3) in water as probed by X-ray photoelectron spectroscopy

The sorption behavior is studied and the physicochemical neptunium species existing on the surface of goethite (α-FeOOH), maghemite (γ-Fe₂O₃), and hematite (α-Fe₂O₃) are determined. Solvent extraction and X-ray photoelectron spectroscopy (XPS) are used to determine the neptunium surface species. The ion and elemental composition of the surface of the minerals and surface neptunyl NpO ₂ ⁺ complexes is determined using these data. Compounds containing neptunium(IV) or neptunium(VI) ions do not appear; rather, neptunyl (Np(V)O ₂ ⁺ group is complexed with surface hydroxide groups of α-FeOOH, γ-Fe₂O₃, and α-Fe₂O₃. Presumably, the oxygen atoms of iron oxides and water and/or carbonate (CO ₃ ^2- ) or nitrate (NO ₃ ^- ) group lie in the equatorial plane of the neptunyl (NpO ₂ ⁺ ) group.     

Étude des réactions d'oxydo—réduction du neptunium dans le mélange Rbcl—CsCl (25–75% mol)

The oxidation—reduction reactions o f neptunium in molten RbCl—CsCl.Standard potentials of the systems NpO₂(VI)—NpO₂(V) and Np(IV)—Np(III) and the equilibrium constant of the following disproportionation reaction 2NP⁴⁺ + 2H₂O + 2Cl^- ? NpO⁺₂ + Np³⁺+ 4HCI have been determined in a (Rb 0,25; Cs 0,75 )C1 melt in the temperature range 660—750°C by absorption spectrophotometry. The results are com- pared with those obtained previously in (Li 0,7; K 0,3)C1, (Li, K)C1 eutectic and (Li 0,55; CsO,45)Cl.     

Thermal stability and degradation kinetic study of white and colored cotton fibers by thermogravimetric analysis

Complexation of neptunium(V) with fluoride in aqueous solutions at elevated temperatures was studied by spectrophotometry and microcalorimetry. Two successive complexes, NpO₂F(aq) and NpO₂F₂⁻, were identified by spectrophotometry in the temperature range of 10–70°C. Thermodynamic parameters, including the equilibrium constants and enthalpy of complexation between Np(V) and fluoride at 10–70°C were determined. Results show that the complexation of Np(V) with fluoride is endothermic and that the complexation is enhanced by the increase in temperature — a two-fold increase in the stability constants of NpO₂F(aq) and more than five-fold increase in the stability constants of NpO₂F₂⁻ as the temperature is increased from 10 to 70°C.     

Sorption of neptunyl(V) cations on suspended silicate: Effects of pH, ionic strength, complexing anions, humic acid, and metal ions

Sorption of NpO₂ ⁺ on silicate (10.00 g/l) particles dispersed in sodium perchlorate media was studied as a function of pcH and ionic strength at 298 K. The sorption increased with increased pcH in the range of ∼6.5 to 9.2, above which saturation was observed. An increase in ionic strength from 0.20M to 1.00M (NaClO₄), increased the NpO₂ ⁺ sorption, which then decreased at 1.50M (NaClO₄) for 7<pcH<8.5. The effects of different types of ligands on the sorption of NpO₂ ⁺ to suspended silicate were investigated. The types of ligands included: (i) inorganic anions (fluoride, carbonate, phosphate (ii) N-donors (ethylenediamine, 1,10 phenanthroline (iii) carboxylic acids (oxalic acid, citric acid, iminodiacetic acid, ethylenediaminetetraacetic acid) and (iv) humic acid. A synergistic enhancement in sorption to the suspended silicate was observed for phosphate, oxalate, ethylenediaminetetraacetic acid, ethylenediamine, 1,10 phenanthroline (5<pcH<8) and humic acid (6.5<pcH<8.8). This behavior was attributed to the formation of ternary NpO₂ ⁺/silicate/ligand complexes. The effects of Ca(II) (1.00·10⁻³M) and Eu(III) (1.00·10⁻⁴ and 1.00·10⁻³M) ions on NpO₂ ⁺ sorption to suspended silicate were also investigated. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India.     

Effect of fulvic acid and ionic strength on the sorption of radiostrontium on Chinese calcareous soil and its solid components

Summary The sorption and desorption of radionuclide ⁹⁰Sr²⁺were investigated on untreated calcareous soil and two treated soils to remove organic matter and calcium carbonate using batch technique. The experiments were carried out at ambient condition, pH 7.8±0.1 and in the presence of 0.001M NaCl. Effects of fulvic acid and ionic strength on the sorption of ⁹⁰Sr²⁺on calcareous soil were also studied. It was found that the sorption isotherms are linear in the strontium concentration range used herein, and the sorption of ⁹⁰Sr²⁺on the calcareous soil can be described as a reversible sorption process and the sorption mechanism is mainly ion-exchange. The sorption is dependent on ionic strength, and fulvic acid enhances the sorption of ⁹⁰Sr²⁺on calcareous soil. Organic matter present in the calcareous soil is a significant trap of ⁹⁰Sr²⁺and is responsible for the sorption.     

Sorption and desorption of radioselenium on calcareous soil and its solid components

The effect of different solid soil components of calcareous soils on the retention of SeO₃ has been investigated by a batch technique and selective extraction method. The sorption and desorption isotherms of SeO₃ on the untreated calcareous soil and the three treated soils were determined at 20°C, pH 7.8±0.2 and in the presence of 0.001M CaCl₂. It was found that all isotherms are linear, the sorption-desorption hysteresis for untreated soil and treated soils is obvious and the retention of SeO₃ in calcareous soil is mainly attributed to the oxides.     

Sorption and desorption of radioiodine and radioselenium on calcareous soil and its solid components

This paper is an extension of previous papers^1–3. The breakthrough curves and the displacement curves of¹²⁵I⁻ and⁷⁵SeO₃ on the calcareous soil, the treated soil to remove CaCO₃ and the treated soil to remove organic matter were determined at pH 7.8, at 20°C and in the presence of 1·10⁻³ or 1·10⁻⁴ mol/l CaCl₂. These results from column experiments and from batch experiments in the previous papers^1,2 were mutually complementary. It can be definitely concluded that iodide is retained to a very small degree and tetravalent-selenium is retained to a small degree by calcareous soil and that organic matter in calcareous soil acts as a significant trap of iodide and CaCO₃ acts as a trap of tetravalent selenium. Iodide and tetravalent-selenium would be expected to have relatively high dissemination in calcareous soil.     

Sorption and desorption of radiostrontium on calcareous soil and its solid components

The effect of different solid components of calcareous soil on the retention of Sr was investigated by using batch technique and selective extraction method. The sorption and desorption isotherms of Sr on the untreated calcareous soil and the three treated soils were determined at 20°C, pH 7.8±0.2 and in the presence of 0.001 M CaCl₂. It was found that all isotherms are linear and that the sorption of Sr on the calcareous soil can be described by a reversible sorption process and the sorption mechanism is mainly ion exchange.     

Oxidation State of Neptunium and Plutonium and Their Leaching from Sodium–Aluminum–(Iron) Phosphate Glasses

The oxidation states of neptunium and plutonium in doped sodium–aluminum–(iron) phosphate glasses have been determined by X-ray photoelectron spectroscopy. Neptunium is present in the form of Np(IV) as Np⁴⁺ and, in smaller amounts, in the form of Np(V) as neptunyl ions. Plutonium is present mainly in the form of Pu(IV) and additionally Pu(III). The most easily water-leachable element is neptunium, which is attributed to its existence in the mobile form of neptunyl (NpO₂)⁺. The leaching rates of plutonium and impurity americium are approximately two orders of magnitude lower.     

Sorption and desorption of radioselenium on calcareous soil and its solid components

The effect of different solid soil components of calcareous soils on the retention of SeO₃ has been investigated by a batch technique and selective extraction method. The sorption and desorption isotherms of SeO₃ on the untreated calcareous soil and the three treated soils were determined at 20°C, pH 7.8±0.2 and in the presence of 0.001M CaCl₂. It was found that all isotherms are linear, the sorption-desorption hysteresis for untreated soil and treated soils is obvious and the retention of SeO₃ in calcareous soil is mainly attributed to the oxides.     

Raman spectroscopic study on NpO2 +–Ca2+ interaction in highly concentrated calcium chloride

Coordination circumstance of neptunyl ion in concentrated CaCl₂ solutions was analyzed by Raman spectrometry. Besides the symmetric stretch (ν₁) mode of NpO₂ ⁺ and NpO₂ ²⁺, the asymmetric stretch (ν₃) mode of NpO₂ ⁺ was found. The Raman intensity of the ν₃ mode increased with the concentration of CaCl₂ in the system. This would be attributable to the cation–cation interaction between Np(V) and Ca(II).     

Pentakis(carbamide)dioxoneptunium(V) Nitrate [NpO2{OC(NH2)2}5](NO3): Synthesis,Crystal Structure,and Some Properties

X-ray diffraction and spectroscopic data for a new Np(V) compound, namely, [NpO₂{OC(NH₂)₂}₅](NO₃) (I) are presented. Crystals are monoclinic, space group P2₁, a = 11.142(2) Å, b = 7.6379(9) Å, c = 11.143(2) Å, = 108.9(1)°, Z = 2, V = 897.1(2) ų. The neptunium atom has a typical pentagonal-bipyramidal environment with five oxygen atoms of the carbamide molecules in the equatorial plane. The nitrate ion is in the outer sphere. Carbamide is a strong molecular ligand with respect to Np(V) and hence, cation–cation bonds of the NpO₂ ⁺ ions are not realized in structure I. The wave length of the f–f transition in the electronic absorption spectra of crystalline complex I and Np(V) in a saturated carbamide solution is virtually the same and is equal to 991 nm.     

Étude quantitative d'équilibres chimiques en solution dans les sels fondus par spectrophotométrie d'absorption: Application au neptunium

The following reactions: NpO₂⁺+4 HCl ? Np⁴⁺ + 2 H₂O + $\text{1}\text{2}$ Cl₂ + 3Cl^- NpO₂⁺+$\text{1}\text{2}$ Cl₂ ? NpO₂²⁺ +Cl^- 2HCl+O^2- ? H₂O +Cl^- have been examined quantitatively. The reactions were studied in fused LiCl-KCl sparged with gas mixtures of definite compositions. The concentrations of the diffrent neptunium species were measured by absorption spectrophotometry. The values of respective equilibrium constants are: K = (9.3±0.4)· 10^-6 atm(^{-$\text{1}\text{2}$}); K₁ = (2.3±0.1)·10^-2 atm(^{-$\text{1}\text{2}$}); k = 10^3.8 1 mol^-1 atm^-1 The standard potential of the system NpO₂²⁺ / NpO₂⁺ was determinedto be E⁰ = 0.220 V (vs.standard chlorine electrode).     

Speciation and solubility of neptunium in underground environments by paper electrophoresis

Speciation and solubility of neptunium were studied using paper electrophoresis, ion exchange and ultrafiltration. Among these methods, the paper electrophoresis was found to be suitable for measuring speciation and solubility of neptunium of low concentration, if chemical species had opposite charge each other or dissolved species had a charge. Using paper electrophoresis, hydrolysis constants of NpO₂OH⁰ and NpO ₂ ^– (OH) ₂ ^– and solubility product of NpO₂ were obtained and ionic-strength dependence of speciation was observed.     

Mössbauer spectroscopy of237Np in solid solutions of actinide dioxides

Emission Mössbauer (nuclear gamma-resonance) spectra of²³⁷Np resulting from the alpha-decay of²⁴¹Am in solid solutions AmO₂–ThO₂ and AmO₂–UO₂ prepared by precipitation from LiF–NaF eutectic melts under fluorine-oxygen exchange were first investigated in the temperature range from 77 to 296 K. The resonant absorbers are NpO₂ and NpAl₂. The possibility is stated of managing the form of the emission Mössbauer spectra of²³⁷Np in dioxides by the directed change of the matrix stoichiometry or by its irradiation by visible light. At temperatures from 77 to 230 K the authors measured for the first time the NGR absorption spectra of²³⁷Np in solid solution NpO₂–ThO₂ with various concentrations of neptunium dioxide. An increase of the absorption line width (approximately by a factor of 4) with a decrease in the NpO₂ contents (to 10 mol.%) was explained by the influence of fast electron exchange between Np⁴⁺ and Np⁵⁺ states observed in the NpO₂–ThO₂ solid solution at low concentrations of neptunium dioxide.     

Sorption and desorption of radioiodine on calcareous soil and its solid components

The effect of different solid components of calcareous soil on the retention of I was investigated by a batch technique and selective extraction method, and the effect of -irradiation was also investigated. The sorption and desorption isotherms of I on the one untreated, three treated soils and the calcareous soil irradiated with -rays were determined at 30 °C, pH 8.1±0.2 and in the presence of 1.0×10^–4M or 0.67×10^–5M CaCl₂. It was found that the sorption-desorption hysteresis on the calcareous soil actually occurs on the same time scale, that iodine can be easily transported in the calcareous soil and that the exceptionally high contribution of organic matter to the iodine sorption is demonstrated.     

Dosage spectrophotometrique du neptunium

(Spectrophotometric determination of neptunium.) Use of the absorption peak of the NpO⁺₂ ion at 981 nm is discussed. Quantitative conversion to Np(V) requires oxidation of Np(IV) by Ce(IV), reduction of Np(VI) and excess of Ce(IV) with hydrazinium nitrate, and destruction of excess of hydrazine by nitrite. The measurable concentration range in the cuvette is 2–1000 mg l^-1 and the precision is± 1% in the higher range. Uranium and plutonium at ratios Me/Np ? 10^-3 do not interfere.     

A pulse radiolysis study of the reactivity of neptunoyl ions relative to inorganic free radicals

Conclusions 1. Pulse radiolysis was used to find the rate constants for the reactions of OH, HSO₄, NO₃, and Cl₂ radicals with neptunoyl ions.Change in the NO₃ and H⁺ ion concentrations do not affect the term k[NO₃ + NpO₂ ⁺], while k[Cl₂ ^– + NpO₂ ⁺] increases with increasing chloride concentration due to the formation of neptunoyl ion chlorocomplexes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 456–458, February, 1986.     

Sensitive redox speciation of neptunium by CE–ICP–MS

Capillary electrophoresis (CE) was used to separate the neptunium oxidation states Np(IV) and Np(V), which are the only oxidation states of Np that are stable under environmental conditions. The CE setup was coupled to an inductively coupled plasma mass spectrometer (Agilent 7500ce) using a Mira Mist CE nebulizer and a Scott-type spray chamber. The combination of the separation capacity of CE with the detection sensitivity of inductively coupled plasma mass spectrometry (ICP-MS) allows identification and quantification of Np(IV) and Np(V) at the trace levels expected in the far field of a nuclear waste repository. Limits of detection of 1?×?10^-9 and 5?×?10^-10 mol L^-1 for Np(IV) and Np(V), respectively, were achieved, with a linear range from 10^-9 to 10^-6 mol L^-1. The method was applied to study the redox speciation of the Np remaining in solution after interaction of 5?×?10^-7 mol L^-1 Np(V) with Opalinus Clay. Under mildly oxidizing conditions, a Np sorption of 31% was found, with all the Np remaining in solution being Np(V). A second sorption experiment performed in the presence of Fe²⁺ led to complete sorption of the Np onto the clay. After desorption with HClO₄, a mixture of Np(IV) and Np(V) was found in solution by CE–ICP–MS, indicating that some of the sorbed Np had been reduced to Np(IV) by Fe²⁺.