Nanostructured Magnetic Sorbents for Selective Recovery of Uranium(VI) from Aqueous Solutions

Direct sol-gel, novel template, and additional high-temperature reduction procedures for preparing iron oxides and their composites, showing promise for selective sorption of dissolved U(VI) from aqueous media of various acidities, are described. The sorption activity of the materials was studied, the kinetic curves of the sorption were obtained, and the efficiency of the selective recovery of U(VI) from aqueous solutions with different pH values using the new sorbents was compared. The probable mechanism of the U(VI) sorption onto the sorbents studied was suggested on the basis of SEM, XPS, emf, and BET data. The quantitative sorption of U(VI) is determined to a greater extent by the composition of the sorbent solid phase, rather then by the specific surface area of the sorbents, which ranges from 0.1 to 47.3 m² g^?1 depending on the synthesis procedure. The crystalline Fe⁰ phase in the sorbents prepared using additional high-temperature reduction plays the key role in the U(VI) sorption by the reducing deposition mechanism. The saturation magnetization for this type of sorbents can reach 133–140 emu g^?1, which is an additional advantage allowing magnetic separation of the spent sorbents from the treated solutions.

     

Removal of U(VI) from simulated liquid waste using synthetic organic resin

Poly(acrylic acid–dimethylaminoethyl methacrylate) was prepared by γ-radiation-induced copolymerization at a radiation dose of 60 kGy and a dose rate of 1.25 kGy h^–1. The resin obtained was used to remove U(VI) from simulated solution of the waste from the Fuel Manufacturing Pilot Plant (FMPP). A preliminary test of U(VI) adsorption onto the resin showed high affinity of this resin for U(VI) ions. The adsorption behavior toward the U(VI) ions was studied in relation to the contact time, pH, temperature, resin dosage, and initial concentration of metal ions. The adsorption isotherms of uranium onto the resin were described using the Langmuir and Freundlich models, with the Langmuir model being more adequate to the experimental equilibrium data. Without foreign ions, the maximum adsorption capacity of the resin for U(VI) was 105.7 mg g^–1. X-ray fluorescence was used to evaluate the amount of U(VI) ions on the resin sample before and after the adsorption.     

Sorption of U(VI) onto layered double hydroxides and oxides of Mg and Al,prepared using microwave radiation

Layered double hydroxides of Mg and Al, containing CО₃^2– ions in the interlayer space (LDH-Mg-Al-CО₃), and layered double oxides of Mg and Al (LDO-Mg-Al) were prepared using microwave radiation (MWR). The use of MWR allows not only acceleration of the synthesis of both LDH and LDO, but also preparation of compounds with high kinetic characteristics of the U(VI) sorption. The degree of U(VI) sorption (α) from 10^–2 M aqueous U(VI) solutions at a sorption time of 4 h and V/m = 50 mL g^–1 exceeds 99.0%. In sorption from more concentrated (10^–1 M) aqueous U(VI) solutions under similar conditions, α on all the samples does not exceed 37.5%.     

Solid phase extractive preconcentration of some actinide elements using impregnated carbon

Apricot stone shells were carbonized under certain chemical and thermal conditions, and the resulting charcoal was impregnated with oxalic and succinic acids of different concentrations. The sorbents were physically characterized and used for preconcentration of U(VI) and Th(IV) from acidified aqueous solutions. Batch equilibrium studies revealed that a quantitative preconcentration could be achieved at pH ∼2 for U(VI) and ∼1.3 for Th(IV). The equilibration time was up to 24 h for U(VI) and 40 min for Th(IV). The modified sorbent showed a superior extraction ability for U(VI) and Th(IV) with the mean distribution coefficients (K _d) of 2084 and 7808 ml g⁻¹, respectively. The sorption capacity was found to be 2.39 and 8.47 mg g⁻¹ for U(VI) and Th(IV) on apricot stone anchored with oxalic acid and 2.3 and 9.18 mg g⁻¹ for the sorbent anchored with succinic acid, respectively. Desorption of the loaded uranium ions was effectively achieved using 1 M HNO₃, whereas only 0.5 M HNO₃ was recommended to release the retained thorium ions. Published in Russian in Radiokhimiya, 2008, Vol. 50, No. 1, pp. 50–56. The text was submitted by the authors in English.     

Sorption of neptunium in the highest oxidation states from alkaline solutions with complexing fibrous “filled” sorbents

Sorption of Np(VII), Np(VI), and Np(V) from 1 M NaOH by complexing fibrous “filled” sorbents was examined. POLIORGS 33-n and 34-n sorbents containing amidoxime and hydrazidine groups efficiently recover Np in the highest oxidation states and exhibit good kinetic properties. During sorption, Np(VII) is reduced with the sorbent to Np(VI) having a higher, under the actual conditions, distribution coefficient. The distribution coefficients, ml g^?1, were estimated at 4.6 × 10³ for Np(VII), 1.4 × 10⁴ for Np(VI), and 3.6 × 10² for Np(V).     

Phosphoryl-Containing Chelating Sorbents for Concentrating Actinides

New chelating sorbents with phosphinate, carbamoylmethylphosphinate, and methylenediphosphine dioxide functionalities are synthesized by chemical and noncovalent binding of the ligands to polymer matrices, chloromethylated styrene copolymer and XAD-7 acrylate polymer. The sorption and kinetic characteristics of the sorbents with respect to U(VI), Th(IV), Pu(IV), and Am(III) are studied in nitric acid solutions. The sorbents obtained by noncovalent binding of the ligands to XAD-7 demonstrate better kinetic properties. The sorbents can be used for concentrating actinides from 3–5 M HNO₃ and for their partitioning.     

Sorption of CH3 131I from a water vapor-air flow onto inorganic sorbents containing Ag and nonferrous metals (Cu,Ni, Zn)

Sorption of CH₃ ¹³¹I from a water vapor-air medium onto Fizkhimin inorganic sorbents containing Ag and nonferrous metals (Cu, Ni, Zn) was studied. Ag-free Fizkhimin inorganic sorbents exhibit poor ability to take up CH₃ ¹³¹I. No more than 51% of the initial 10-mg portion of CH₃ ¹³¹I is taken up by the sorbents heated to 350°C. The sorbents containing 1.4–2 wt % Ag and 5.6–8 wt % nonferrous metal (Cu, Ni, Zn) show high ability to take up CH₃ ¹³¹I (>99.8% uptake), with the performance of the Ni-containing sorbents remaining very high (>99.9%) with variation of various parameters of both the sorbents and the medium. The Cu- and Zn-containing analogs do not exhibit such properties.     

Sorption of U(VI) with soil from the region of location of the Novi Khan radioactive waste repository in Bulgaria

Sorption of U(VI) with soil from the region of location of the radioactive waste repository was studied. The radionuclide ²³⁷U produced by the photonuclear reaction ²³⁸U(γ, n)²³⁷U on an electron accelerator, MT-25 microtron (FLNR, JINR), was used as tracer. The U(VI) speciation in solution at various U concentrations was calculated in the range pH 1–7 using the Speciation program.     

Solubility of mixed-valence U(IV–VI) and Np(IV–V) hydroxides in simulated groundwater and 0.1 M NaClO4 solutions

The kinetics of U(VI) accumulation in the phase of U(IV) hydroxide and of Np(V) in the phase of neptunium(IV) hydroxide, and also the solubility of the formed mixed-valence U(IV)-U(IV) and Np(IV)-Np(V) hydroxides in simulated groundwater (SGW, pH 8.5) and 0.1 M NaClO₄ (pH 6.9) solutions was studied. It was found that the structure of the mixed U(IV–VI) hydroxide obtained by both oxidation of U(IV) hydroxide with atmospheric oxygen and alkaline precipitation from aqueous solution containing simultaneously U(IV) and U(VI) did not affect its solubility at the U(VI) content in the system exceeding 16%. The solubility of mixed-valence U(IV–VI) hydroxides in SGW and 0.1 M NaClO₄ is (3.6±1.9) × 10^?4 and (4.3 ± 1.7) × 10^?4 M, respectively. The mixed Np(IV–V) hydroxide containing from 8 to 90% Np(V) has a peculiar structure controlling its properties. The solubility of the mixed-valence Np(IV–V) hydroxide in SGW [(6.5 ± 1.5) × 10^?6 M] and 0.1 M NaClO₄ [(6.1±2.4) × 10^?6 M] is virtually equal. Its solubility is about three orders of magnitude as high as that of pure Np(OH)₄ (10^?9–10^?8 M), but considerably smaller than that of NpO₂(OH) (～7 × 10^?4 M). The solubility is independent of the preparation procedure [oxidation of Np(OH)₄ with atmospheric oxygen or precipitation from Np(IV) + Np(V) solutions]. The solubility of the mixed-valence Np hydroxide does not increase and even somewhat decreases [to (1.4±0.7) × 10^?6 M] in the course of prolonged storage (for more than a year).     

Localization of CH<Subscript>3</Subscript><Superscript>131</Superscript>I from Water vapor–Air flow on granulated sorbents containing nanoparticles of Ag and Ni compounds

Sorption of CH₃ ¹³¹I from the water vapor–air medium onto Fizkhimin inorganic sorbents containing nanoparticles of Ag and Ni compounds was studied. The developed solvents containing 2 wt % Ag and 4–10 wt % Ni exhibit high performance in CH₃ ¹³¹I sorption (>99.9% uptake). The sorption efficiency remains very high (>99.9%) as characteristics of the sorbents and the medium are varied.     

Determination of the Parameters of Selective <Superscript>137</Superscript>Cs Sorption onto Natural and Ferrocyanide-Modified Glauconite and Clinoptilolite

The effect exerted by surface modification of natural aluminosilicates, glauconite and clinoptilolite, with ferrocyanides on the parameters of selective ¹³⁷Cs sorption was studied. The modification leads to an increase in the specific sorption and in the radiocesium interception potential in the presence of potassium, RIP(K). RIP(K) of the modified sorbents NPF-Gl and NPF-Cl was 6.1 × 10⁵ and 5.0 × 10⁶ mmol kg^–1, and the specific sorption capacity, 138 ± 14 and 136 ± 12 mg g^–1, respectively. The regular trends in variation of the ¹³⁷Cs distribution coefficients in sorption onto the natural and modified sorbents at K⁺ and Са²⁺ concentrations ranging from 10^–4 to 2.0 M were found. The modified sorbents exhibit high specificity to ¹³⁷Cs in a wide range of Ca and K concentrations in the solutions.     

Sorption of Mo(VI) on zirconium molybdosilicate gel and potential application as a <Superscript>99</Superscript>Mo/<Superscript>99<Emphasis Type="Italic">m</Emphasis> </Superscript>Tc generator

Sorption of Mo(VI) from aqueous nitrate solutions onto zirconium molybdosilicate (ZrMoSi) gel was studied using ⁹⁹Mo radiotracer. The acid–base titration curve showed that the prepared ZrMoSi gel was an amphoteric material with the point of zero charge (PZC) at pH 2.5. The highest distribution coefficient (600 mL g^–1) of ⁹⁹Mo(VI) on ZrMoSi from nitrate media was achieved at pH 2.1. The sorption kinetics of ⁹⁹Mo(VI) onto ZrMoSi obeyed the pseudo-second-order model. The breakthrough sorption capacity of ZrMoSi gel was found to be 4.25 × 10^–2 [mmol Mo(VI)] g^–1. The prepared ⁹⁹Mo/^99mTc chromatographic column generator showed a good performance: The ^99mTc elution yield was 87.7%, pH of the eluate ranged from 5.6 to 7.2, and the radionuclidic purity of the eluted ^99mTc was >99.99% with a radiochemical purity of 98.31% (as ^99mTcO₄^–).     

Montmorillonite modified with polyethylenimines as a sorbent for recovering U(VI) from wastewaters

Clay minerals modified with polyethylenimines (Mn-t-PEI) show promise for sorption treatment of wastewaters to remove U(VI) and for U(VI) preconcentration in determination of its low concentrations. Conditions are found for preparing modified sorbents: The optimal pH range for PEI sorption to prepare the modified sorbents is ≥9.0, which suggests electrostatic interaction of PEI with montmorillonite. The maximal sorption of the linear and branched polymers on montmorillonite, calculated from the sorption isotherms, is 0.32–0.38 g PEI/g mineral. The U(VI) sorption value on natural montmorillonite is considerably lower than on Mn-t-PEI, where the isotherm at low U(VI) concentrations is practically linear and the degree of U(VI) sorption exceeds 97% (depending on the uranium content).     

Physicochemical principles of preparation of U(VI) carbonate solutions for extraction reprocessing in the Carbex process

Physicochemical principles of preparation of U(VI) carbonate solutions in the step of oxidative dissolution of U₃O₈ and UO₂ in the Carbex process are considered. Carbonate solutions with the U(VI) concentration higher than 100 g L^–1, suitable for subsequent final purification of uranium by extraction, can be prepared under the conditions of formation of U(VI) carbonate–peroxide complexes in the course of dissolution with prevention of hydrolysis of U(VI) compounds. The behavior of impurities simulating some fission products in the course of oxidative dissolution was studied, and the decontamination factors of U(VI) from the chosen simulated fission products were determined.     

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.     

Layered double hydroxides intercalated with EDTA as effective sorbents for U(VI) recovery from wastewater

The performance of the synthetic hydrotalcite-like sorbents, initial {[Zn₄Al₂(OH)₁₂]CO₃·nH₂O} and heat-treated (Zn₄Al₂O₇) forms and the form intercalated with EDTA and prepared in a nitrogen atmosphere from [Zn₄Al₂(OH)₁₂]Cl₂·nH₂O, was evaluated and compared. Increased concentrations of hydrocarbonate and carbonate ions do not noticeably affect the degree of U(VI) recovery from wastewaters with pH 8, which is due to tight binding of U(VI) with EDTA anions in the interlayer space of layered double hydroxides. [Zn₄Al₂(OH)₁₂]EDTA·nH₂O is one of the most effective and cheapest synthetic sorbents for recovering from aqueous media not only cationic but also anionic U(VI) species, which is particularly important. Therefore, the sorbent can be recommended for practical use.     

Sorption of U(VI) from aqueous solutions with carbon sorbents

The sorption characteristics of ordinary and oxidized sorts of synthetic (SKN) and kernel (KAU) carbons and also carbon fabric oxidized with HNO₃ (AUTo) with respect to U(VI) were studied. The influence of solution pH on the sorption capacity of carbon materials with respect to uranium was elucidated. The influence of chlorine and sulfate anions on the sorption rate and sorption capacity was studied. Based on kinetic curves and sorption isotherms of uranyl ions and their derivatives, possible mechanisms of uranium adsorption with carbon sorbents were considered. It was shown that carbon sorbents can be used for treatment of aqueous media, among them drinking water, to remove U(VI) compounds.     

Characterization and determination of the thermodynamic and kinetic properties of the adsorption of molybdenum (VI) onto microcrystalline anthracene modified with 8-hydroxyquinoline

A reliable and effective method for the determination of trace molybdenum in effluents is proposed. Molybdenum (VI) is analyzed by Microwave Plasma Torch Optical Emission Spectrometry (MPT-OES) based on the adsorption collection onto microcrystalline anthracene modified with 8-hydroxyquinoline. The possible reaction mechanism was discussed in detail and the optimum conditions for adsorption of Mo (VI) were confirmed. The experimental data were fitted well with the pseudo-second-order kinetic model and Langmuir model at all studied temperatures. The calculated thermodynamic parameters (ΔG^?, ΔH^? and ΔS^?) showed that the adsorption of molybdenum onto microcrystalline anthracene was feasible, spontaneous and endothermic at 280–320 K. The recovery of this method is in the range of 96.5%–103.3% with preconcentration factor of 100 and the limit detection after preconcentration is 0.078 μg L^? 1. The proposed method has been successfully applied to the determination of trace Mo (VI) in environmental water samples with satisfactory results.     

Chelating agent-free solid phase extraction (CAF-SPE) of uranium,cadmium and lead by Fe-Al-Mn nanocomposite from aqueous solution

Fe-Al-Mn nanocomposite has been synthesized by impregnating MnO₂ with Fe and Al nitrate aqueous solution for preconcentration and determination of Pb (II), Cd (II) and U (VI) ions from aqueous solution. Fourier Transform Infrared spectroscopy (FTIR), X-Ray-diffraction (XRD) and Scanning electron microscopy coupled with energy dispersive&nbsp;X-ray detector (SEM–EDX) were employed to characterize the as-synthesized nanocomposite. The XRD result indicates that the as-synthesized nanocomposite had a crystal size with rhombohedral structure and size of 30.81 nm. FTIR results confirmed the presence of hydroxyl group and Metal–Oxygen vibration in the adsorbent. A sensitive and simple solid-phase preconcentration procedure for the determination of trace amounts of Pb(II) and Cd(II) ions by FAAS and U(VI) ions by Uv–Vis was developed. The adsorption isotherm was formally described by both Langmuir and Freundlich equation with a maximum adsorption capacity of 12.5 (Pb), 12.8(Cd) and 14.9(U) mg g^?1 respectively with preconcentration factor of 15. The limits of detection were 0.09, 0.05 and 0.0097 mg L^?1 and the relative standard deviation for ten replicate measurements were 2.47, 0.979 and 2.04%, for Pb (II), Cd(II) and U(VI) ions, respectively. The recovery of Pb(II), Cd(II) and U(VI) ions were found to be 92.7, 91.3, and 81.76%, respectively. On the basis of these findings, the as-synthesized Fe-Al-Mn nanocomposite was successfully applied as a solid phase extraction for preconcentration and determination of Pb(II), Cd(II) and U(VI) ions in aqueous solution.

     

Extraction of REE(III), U(VI), and Th(IV) from Nitric Acid Solutions with Carbamoylmethylphosphine Oxides in the Presence of Bis[(trifluoromethyl)sulfonyl]imide Ions

Extraction of microamounts of REE(III), U(VI), and Th(IV) with solutions of carbamoylmethylphosphine oxides (CMPOs) in organic diluents from aqueous HNO₃ solutions containing lithium bis[(trifluoromethyl) sulfonyl]imide (LiTf₂N) was studied. The efficiency of the REE(III), U(VI), and Th(IV) extraction from nitric acid solutions with CMPO solutions considerably increases in the presence of Tf₂N^– ions in the aqueous phase. The stoichiometry of the extractable complexes was determined, and the influence of the structure of the CMPO molecule, kind of organic diluent, and aqueous phase composition on the efficiency of the U(VI), Th(IV), and REE(III) extraction into the organic phase was considered.