Uranium Preconcentration with a Chelating Sorbent Based on Maleic Anhydride–Styrene Copolymer

The ability of a chelating sorbent based on maleic anhydride–styrene copolymer to take up uranium was studied. The sorbent was prepared by modification of the copolymer with Norsulfazolum in the presence of formaldehyde. The dependence of the sorption capacity on the solution acidity was studied. At pH 5, the degree of sorption passes through a maximum. As the uranium concentration in the solution is increased, the amount of the sorbed metal increases, reaching a maximum at a concentration of 8 × 10^–3 M (SC = 1253 mg g^–1). The influence of the solution ionic strength on the uranium sorption was examined. The ionic strength of up to 0.4 M does not affect the sorption, but as the ionic strength is increased further, the sorption decreases, first gradually and then sharply. The desorption of the sorbed uranium ions was studied. The effect of mineral and organic acids on the uranium desorption was examined. The desorption is maximal with HClO₄.     

Sorption Power of the New Generation of Phytosorbents with Respect to Uranium

The sorption power of a new class of sorbents, phytosorbents, with respect to uranium was studied in model solution and real waters. Sorption was studied as influenced by the specific mass of the sorbent. The kinetic parameters of the sorption were determined, and diffusion inside the sorbent grain was identified as the limiting stage of the process. The diffusion coefficients were calculated; the exchange half-times were determined and confirmed. The uranium sorption was studied as influenced by pH. The maximal sorption of uranium is achieved at pH <4. The exchange capacities of the sorbents were determined.     

Solid phase extraction using silica gel modified with murexide for preconcentration of uranium (VI) ions from water samples

Murexide was chemically bonded to silica gel surface immobilized 3-aminopropyl trimethoxysilane (APMS) to produce the new sorbent. A solid phase extraction method using the new sorbent has been developed to separate and concentrate trace amount of uranium (VI) from aqueous samples for the measurement by spectrophotometry method using Arsenazo III reagent. The influences of some analytical parameters on the quantitative recoveries of the analyte were investigated both in batch and column methods. Quantitative recovery of U(VI) was achieved by stripping with 0.1 mol L(-1) HCl. The maximum sorption capacity of the modified silica gel was 1.13 mmol g(-1) U(VI). A high preconcentration factor value of 400 with a lower limit of detection of 1 microg L(-1) was obtained for U(VI). The practical applicability of the developed sorbent was examined using synthetic and real samples such as sea/ground water samples.     

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.     

Effects of EDTA and NTA on sorption of U(VI) on the clay fraction of soil

Sorption behavior of U(VI) is studied in model systems containing montmorillonite with various concentrations of humic acids on its surface and complexants (disodium salts of ethylenediaminetetraacetic and nitrilotriacetic acids). Humic acids deposited onto the surface of montmorillonite enhance the U(VI) sorption at pH <7.0. The effect of complexants on the U(VI) sorption is rather intricate because of the possibility of formation of some surface uranium complexes, whose nature depends on the nature and concentration of the complexant in solution, pH, and humic acid concentration on the surface of montmorillonite.     

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.     

Batch sorption dynamics and equilibrium for the removal of cadmium ions from aqueous phase using wheat bran

Studies on a batch sorption process using wheat bran as a low cost sorbent was investigated to remove cadmium ions from aqueous solution. The influence of operational conditions such as contact time, cadmium initial concentration, sorbent mass, temperature, solution initial pH, agitation speed and ionic strength on the sorption kinetics of cadmium was studied. Pseudo-second-order model was evaluated using the six linear forms as well as the non-linear curve fitting analysis method. Modeling of kinetic results shows that sorption process is best described by the pseudo-second-order model using the non-linear method. The sorption of cadmium was found to be dependent on initial concentration, sorbent mass, solution pH, agitation speed, temperature, ionic strength and contact time. The value of activation energy (12.38 kJ mol(-1)) indicates that sorption has a low potential barrier corresponding to a physical process. Sorption equilibrium isotherms at different temperatures was determined and correlated with common isotherm equations such as Langmuir and Freundlich models. It was found that the Langmuir model appears to well fit the isotherm data but a worse correlation was obtained by the Freundlich model. The five Langmuir linear equations as well as the non-linear curve fitting analysis method were discussed. Results show that the non-linear method may be a better way to obtain the Langmuir parameters. Thermodynamic parameters such as DeltaH degrees, DeltaS degrees and DeltaG degrees were calculated. These parameters indicate that the sorption of cadmium by wheat bran is a spontaneous process and physical in nature involving weak forces of attraction and is also endothermic.     

Sorption of Uranium on Zirconium Phosphate Inorganic Cation Exchanger

Uranium sorption on the zirconium phosphate inorganic cation exchanger is studied. Zirconium phosphate (ZP) efficiently sorbs uranium from nitric acid solutions over the pH range 3.0-5.0. The uranium distribution coefficients decrease in the presence of nitrates of alkali and alkaline-earth metals. The kinetics of static desorption of uranium with HNO₃ and also of its dynamic sorption and desorption are studied. The mechanism of U sorption on ZP is analyzed. The exchange rate of the hydrogen ions in the sorbent phase for uranyl ion is controlled by the gel kinetics, and the rate-determining stage is the inner diffusion of uranium in the sorbent grain. The kinetic parameters of this exchange are determined. The sorption rate doubles with increasing temperature from 20 to 40°C and pH from 3.0 to 5.0.     

Biosorption of uranium(VI) from aqueous solution using calcium alginate beads

In this paper, sorption potentials of uranium ions were studied using alginate polymer beads in diluted aqueous solutions. The ability of alginate beads to adsorb uranium(VI) from aqueous solution has been studied at different optimized conditions of pH, U(VI) concentration, contact time, biomass dosage and temperature. In order to determine the adsorption characteristics, Langmuir, Freundlich, and Dubinin–Radushkevich adsorption isotherms were applied to the adsorption data. The thermodynamic parameters such as variations of enthalpy ΔH, entropy ΔS and variation of Gibbs free energy ΔG were calculated from the slope and intercept of ln K_d vs. 1/T plots. The results suggested that alginate beads could be suitable as a sorbent material for adsorption and removal of uranium ions from dilute aqueous solutions.     

Kinetic and equilibrium study for the sorption of cadmium(II) ions from aqueous phase by eucalyptus bark

The efficiency of eucalyptus bark as a low cost sorbent for removing cadmium ions from aqueous solution has been investigated in batch mode. The equilibrium data could be well described by the Langmuir isotherm but a worse fit was obtained by the Freundlich model. The five linearized forms of the Langmuir equation as well as the non-linear curve fitting analysis method were discussed. Results show that the non-linear method may be a better way to obtain the Langmuir parameters. Maximum cadmium uptake obtained at a temperature of 20 degrees C was 14.53mgg(-1). The influence of temperature on the sorption isotherms of cadmium has been also studied. The monolayer sorption capacity increased from 14.53 to 16.47 when the temperature was raised from 20 to 50 degrees C. The DeltaG degrees values were negative, which indicates that the sorption was spontaneous in nature. The effect of experimental parameters such as contact time, cadmium initial concentration, sorbent dose, temperature, solution initial pH, agitation speed, and ionic strength on the sorption kinetics of cadmium was investigated. Pseudo-second-order model was evaluated using the six linear forms as well as the non-linear curve fitting analysis method. Modeling of kinetic results shows that sorption process is best described by the pseudo-second-order model using the non-linear method. The pseudo-second-order model parameters were function of the initial concentration, the sorbent dose, the solution pH, the agitation speed, the temperature, and the ionic strength.     

Determination of kinetic and equilibrium parameters of the batch adsorption of Ni(II) from aqueous solutions by Na-mordenite

The potential to remove nickel(II) ions from aqueous solutions using Na-mordenite, a common zeolite mineral, was thoroughly investigated. The effects of relevant parameters solution pH, adsorbent dose, ionic strength, and temperature on nickel(II) adsorption capacity were examined. The sorption data followed the Langmuir, Freundlich, Langmuir-Freundlich and Dubinin-Radushkevich (D-R) isotherms. The maximum sorption capacity was found to be 5.324 mg/g at pH 6, initial concentration of 40 mg/L and temperature of 20 degrees C. Thermodynamic parameters, viz. changes in standard free energy (DeltaG degrees ), enthalpy (DeltaH degrees ) and entropy (DeltaS degrees ) have also been evaluated and the results show that the sorption process was spontaneous and endothermic in nature. Dynamics of the sorption process were studied and the values of rate constant of adsorption, rate constant of intraparticle diffusion were calculated. The activation energy (E(a)) was found to be 12.465 kJ/mol in the present study, indicating a chemical sorption process involving weak interactions between sorbent and sorbate. The sorption capacity increased with the increase of solution pH and the decrease of ionic strength and adsorbent dose. The nickel(II) ions sorption by the Na-mordenite is not completely attributable to ion exchange. Compared to the other adsorbents, the nickel(II) ions show a lower affinity towards the clay mineral adsorbents.     

Preconcentration of uranium on POLIORGS 34-n fibrous filled sorbent from natural waters

Sorption preconcentration of U(VI) on POLIORGS 34-n fibrous filled sorbent with amidoxime groups from model solutions like natural water was studied under static and dynamic conditions. The equilibrium (distribution coefficient) and kinetic (diffusion coefficient) parameters of the sorption were determined. Parameters of dynamic preconcentration of uranium by sorption on disks and in a column packed with POLIORGS 34-n under indicated conditions were calculated by mathematical modeling using the experimental data.     

Chromium(VI) biosorption by dried Rhizopus arrhizus: effect of salt (NaCl) concentration on equilibrium and kinetic parameters

Some industrial wastewaters contain high quantities of salts besides heavy metal ions. The presence of salt ions leads to high ionic strength, which may significantly affect the performance of the biosorption process so the effect of salts on the biosorption of heavy metal ions should be investigated. In this study the biosorption of chromium(VI) from saline solutions on dried Rhizopus arrhizus was studied as a function of pH, initial chromium(VI) and salt (NaCl) concentrations in a batch system. The biosorption capacity of R. arrhizus strongly depended on solution pH and maximum chromium(VI) sorption capacity of sorbent was obtained at pH 2.0 both in the absence and in the presence of increasing concentrations of salt. Chromium(VI)-salt biosorption studies were performed at this pH value. Equilibrium uptakes of chromium(VI) increased with increasing chromium(VI) concentration up to 250mgl(-1) and decreased considerably by the presence of increasing concentrations of salt. At 100mgl(-1), initial chromium(VI) concentration, dried R. arrhizus biosorbed 78.0mgg(-1) of chromium(VI) in 72h without salt medium. When salt concentration was raised to 50gl(-1), this value dropped to 64.0mgg(-1) of chromium(VI) at the same conditions resulting in 17.9% decrease of biosorption capacity. The equilibrium sorption data were analysed by using Freundlich, Langmuir, Redlich-Peterson and Langmuir-Freundlich (Sips), the two and three parameters adsorption models, using non-linear regression technique and isotherm constants were evaluated depending on salt concentration. The Langmuir-Freundlich (Sips) was the best suitable adsorption model for describing the biosorption of chromium(VI) individually and in salt-containing medium. Pseudo-first-order, pseudo-second-order and saturation type kinetic models described the biosorption kinetics accurately at all chromium(VI) concentrations in the absence and in the presence of changing concentrations of salt. Isotherm and saturation type kinetic constants varied due to the level of salt were expressed as a function of initial salt concentration.     

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.     

不同pH条件下硫化钼纳米片吸附Cd(II)的微观机制研究

本研究结合静态实验和X射线吸收精细结构谱学(EXAFS)评估了硫化钼纳米片对重金属Cd(II)的吸附行为和微观机制。结果表明: Cd(II)在硫化钼纳米片上的吸附受溶液pH、反应时间和温度的显著影响, 但不受离子强度的影响。在pH 3.3~9.6范围内, pH升高显著促进了硫化钼对Cd(II)的吸附量, 但不改变吸收速率、吸附等温线和热力学。二级动力学模型能更好地拟合该吸附平衡, 且内表面颗粒扩散模型显示了吸附过程中的三个典型阶段。等温线和热力学分析说明Cd(II)在硫化钼上的吸附是异质性的、自发的、吸热的和不可逆的过程。EXAFS光谱学分析揭示了该吸附存在两种类型: 在较低的pH(3.56, 6.48)条件下, 内表面络合以Cd-S配位键为主; 在较高的pH(9.57)条件下, 出现Cd(OH)₂沉淀, 且配位键以Cd-O和Cd-Cd的形式存在。这些研究结果对于评估重金属离子和硫化钼纳米片在分子水平上的作用机理提供了新的视野。     

Silver nanoparticles embedded polymer sorbent for preconcentration of uranium from bio-aggressive aqueous media

Adsorptive sorbent for bio-aggressive natural aqueous media like seawater was developed by one pot simultaneous synthesis of silver nanoparticles (Ag nps) and poly(ethylene glycol methacrylate phosphate) (PEGMP) by UV-initiator induced photo-polymerization. The photo-polymerization was carried out by irradiating N,N'-dimethylformamide (DMF) solution containing appropriate amounts of the functional monomer (ethylene glycol methacrylate phosphate), UV initiator (α,α'-dimethoxy-α-phenyl acetophenone), and Ag(+) ions with 365 nm UV light in a multilamps photoreactor. To increase mechanical strength, nano-composite sorbent (Ag@PEGMP) was also reinforced with thermally bonded non-woven poly(propylene) fibrous sheet. Transmission electron microscopy (TEM) of the nano-composite sorbent showed uniform distribution of spherical Ag nanoparticles with particles size ranging from 3 to 6 nm. The maximum amount of Ag(0) that could be anchored in the form of nanoparticles were 5±1 and 10±1 wt.% in self-supported PEGMP and poly(propylene) reinforced PEGMP matrices, respectively. Ag@PEGMP sorbent was found to be stable under ambient conditions for a period of six months. Ag@PEGMP composite sorbent did not exhibit growth at all after incubation with pre-grown Escherichia coli cells, and showed non-adherence of this bacteria to the composite. This indicated that composite sorbent has the bio-resistivity due to bacterial repulsion and bactericidal properties of Ag nanoparticles embedded in the PEGMP. Sorption of U(VI) in PEGMP and Ag@PEGMP nano-composite sorbents from well-stirred seawater was studied to explore the possibility of using it for uranium preconcentration from bio-aggressive aqueous streams. The nano-composite sorbent was used to preconcentrate U(VI) from a process aqueous waste stream.     

Sorption of U(VI) from sulfate solutions with spherically granulated chitosans

Sorption of U(VI) from sulfate solutions with spherically granulated chitosans was examined. It was shown that the best sorption and kinetic characteristics are exhibited by freshly formed and cross-linked chitosan granules. The total static exchange capacity for the freshly formed granules was 0.7 mmol of U(VI) per gram of dry sorbent. The diffusion coefficients and similarity criteria describing the diffusion process parameters were calculated. It was found that, irrespective of the method by which the granules were prepared (freshly formed, cross-linked, air-dried), the dominating process is U(VI) sorption on the surface, mainly controlled by external diffusion. Physicomechanical tests of the films of the irradiated chitosan and cellophane (absorbed dose 100–250 kGy) revealed higher strength characteristics of the irradiated chitosan.     

Influence of the nature of oxygen-containing minerals on their sorption ability toward U(VI)

Sorption of U(VI) on natural and synthetic oxygen-containing minerals was studied. With respect to the sorption ability toward U(VI), natural minerals can be ranked in the order iron-containing > aluminum-containing > silicon-containing, and synthetic minerals, in the order iron-containing ≈ silicon-containing ≫ aluminum-containing. It was demonstrated by the example of Fe(OH)₃, α-FeO(OH), and γ-FeO(OH) that crystalline minerals bind U(VI) at pH values corresponding to natural media (pH > 7.5) better than do amorphous minerals. The ionic strength does not affect the U(VI) sorption owing to formation of strong inner-sphere complexes on the mineral surface. The presence in solution of complexing agents in small amounts can enhance the U(VI) sorption owing to formation of ternary surface complexes, whereas large excess of the ligand decreases the sorption because of the shift of the equilibrium toward formation of soluble complexes migrating in the environment by long distances with water streams.     

Magnetic Sorbents for Removing U(VI) from Aqueous Media

Sorption of U(VI) onto magnetic sorbents from aqueous media was studied. The limiting value of the U(VI) adsorption onto magnetite and magnetic potassium zinc hexacyanoferrate(II) at pH 5.0, calculated from the Langmuir equation, is 125 and 102 μmol g^–1, respectively. Natural components of waters, namely, Na⁺ and Ca²⁺ ions and fulvic acids at concentrations of up to 200 mg dm^–3, do not noticeably influence the U(VI) sorption onto magnetic sorbents. Owing to high selectivity (degree of recovery 87–91%) and possibility of separating the solid phase by magnetic separation, these sorbents show promise for removing U(VI) from mineralized mine water.