Sorption study of uranium on carbon spheres hydrothermal synthesized with glucose from aqueous solution

The ability of oxygen-rich carbon spheres (CSs) produced by hydrothermal carbonization with the glucose has been explored for the removal and recovery of uranium from aqueous solutions. The micro-morphology and structure of CSs were characterized by FT-IR and SEM. The influences of different experimental parameters such as solution pH, initial concentration, contact time, ionic strength and temperature on adsorption were investigated. The CSs showed the highest uranium sorption capacity at initial pH of 6.0 and contact time of 25 min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir isotherm. The thermodynamic parameters, △G°(298 K), △H° and △S° were determined to be ?16.88, 12.09 kJ mol^?1 and 197.87 J mol^?1 K^?1, respectively, which demonstrated the sorption process of CSs towards U(VI) was feasible, spontaneous and endothermic in nature. The adsorbed CSs could be effectively regenerated by 0.05 mol/L HCl solution for the removal and recovery of U(VI). Complete removal (99.9 %) of U(VI) from 1.0 L industry wastewater containing 15.0 mg U(VI) ions was possible with 3.0 g CSs.     

Adsorption of uranium from aqueous solution using biochar produced by hydrothermal carbonization

The ability of biochar produced by hydrothermal carbonization (HTC) has been explored for the removal and recovery of uranium from aqueous solutions. The micro-morphology and structure of HTC were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The influences of different experimental parameters such as solution pH, initial concentration, contact time, ionic strength and temperature on adsorption were investigated. The HTC showed the highest uranium sorption capacity at initial pH of 6.0 and contact time of 50 min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir isotherm. The thermodynamic parameters, △G°(298 K), △H° and △S° were determined to be ?14.4, 36.1 kJ mol^?1 and 169.7 J mol^?1 K^?1, respectively, which demonstrated the sorption process of HTC towards U(VI) was feasible, spontaneous and endothermic in nature. The adsorbed HTC could be effectively regenerated by 0.05 mol/L HCl solution for the removal and recovery of U(VI). Complete removal (99.9 %) of U(VI) from 1.0 L industry wastewater containing 15.0 mg U(VI) ions was possible with 2.0 g HTC.     

Novel graphene oxide/bentonite composite for uranium(VI) adsorption from aqueous solution

A novel graphene oxide/bentonite composite (GO/bentonite) was synthesized and then characterized through powder X-ray diffraction, fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and energy dispersive spectroscopy. Adsorption achieved equilibrium within 10 min. Moreover, U(VI) adsorption on GO/bentonite was highly dependent on solution pH and independent of ionic strength. These characteristics suggested that inner-sphere surface complexes of U(VI) formed on GO/bentonite. The adsorption of U(VI) from aqueous solution on GO/bentonite was fitted to the pseudo-second-order and Freundlich isotherm models. The maximum sorption capacity of GO/bentonite was 234.19 mg g^?1 under neutral pH at 303 K. GO/bentonite is a potentially powerful adsorbent for the efficient removal of U(VI) from aqueous solutions.     

Sorption study of uranium from aqueous solution on ordered mesoporous carbon CMK-3

The ability of ordered mesoporous carbon CMK-3 has been explored for the removal and recovery of uraium from aqueous solutions. The textural properties of CMK-3 were characterized using small-angle X-ray diffraction and N₂ adsorption–desorption, and the BET specific surface area, pore volume and the pore size were 1143.7 m²/g, 1.10 cm³/g and 3.4 nm. The influences of different experimental parameters such as solution pH, initial concentration, contact time, ionic strength and temperature on adsorption were investigated. The CMK-3 showed the highest uranium sorption capacity at initial pH of 6.0 and contact time of 35 min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir and Freundlich isotherm. The thermodynamic parameters, ?G°(298 K), ?H° and ?S° were determined to be ?7.7, 21.5 k J mol^?1 and 98.2 J mol^?1 K^?1, respectively, which demonstrated the sorption process of CMK-3 towards U(VI) was feasible, spontaneous and endothermic in nature. The adsorbed CMK-3 could be effectively regenerated by 0.05 mol/L HCl solution for the removal and recovery of U(VI). Complete removal (99.9 %) of U(VI) from 1.0 L industry wastewater containing 15.0 mg U(VI) ions was possible with 2.0 g CMK-3.     

Removal of uranium(VI) from aqueous solution by apricot shell activated carbon

Uranium is a toxic and radioactive heavy metal found in nuclear effluents and should be treated based on environmental considerations. The adsorption of uranyl cations (UO₂ ²⁺) by apricot shell activated carbon (ASAC) was investigated in a batch system. The effects of pH, contact time, temperature, adsorbent dosage on the adsorption kinetics and equilibrium adsorption isotherms of U(VI) were examined. The U(VI) uptake was fast within the first 60 min and reached an equilibrium state at 120 min. The adsorption process was highly pH dependent and the maximum adsorption was obtained at an initial solution pH of 6.0. Temperature over the range 25–45 °C had little effect on the U(VI) adsorption. The U(VI) removal efficiency increased concurrently with increasing ASAC dosage, whereas the U(VI) adsorption capacity decreased with increasing ASAC dosage. The adsorption process followed both Langmuir and Freundlich isotherms. On the basis of Langmuir model, the maximum adsorption capacity was found to be 59.17 mg U(VI)/g adsorbent. The adsorption kinetics can be very well defined by the pseudo-first-order rate model. The present results suggest that ASAC could be used as an adsorbent for an efficient removal of U(VI) from aqueous solution.     

Adsorptive removal of U(VI) and Th(IV) from aqueous solutions using polymer-based electrospun PEO/PLLA fibrous membranes

Fibrous membranes based on poly(ethylene oxide) and poly(l-lactide) fabricated by electrospinning were evaluated for the first time as substrates for the adsorption of tetravalent thorium (Th(IV)) and hexavalent uranium (U(VI)) from aqueous media. The membranes consisted of microfibers with diameters of approximately 2 μm as revealed by scanning electron microscopy. The adsorption of Th(IV) and U(VI) on the membrane was investigated as a function of pH, ionic strength and initial metal concentration under normal atmospheric conditions. The experimental data indicated increased affinity of the membrane for Th(IV) and U(VI), which was pH depended and reaches maximum values (>90 %) for Th(IV) and U(VI) at pH 3 and pH 6.5, respectively. The maximum adsorption capacity (q _max) at optimum conditions was evaluated from the Langmuir isotherm and was found to amount 50.08 and 9.3 mmol kg^?1 for Th(IV) and U(VI), respectively. In addition, studies on the effect of ionic strength on the adsorption efficiency did not show any significant effect indicating that the adsorption of Th(IV) and U(VI) on the membrane was most probably based on specific interactions and the formation of inner-sphere surface complexes. The significantly higher adsorption efficiency of the membrane for Th(IV) in acidic media (pH ≤ 3) could be utilized for a pH-triggered, selective separation of Th(IV) from U(VI) from aqueous media.     

Application of NKF-6 zeolite for the removal of U(VI) from aqueous solution

To better understand the application of NKF-6 zeolite as an adsorbent for the removal of U(VI) from radionuclides and heavy metal ions polluted water, herein, NKF-6 zeolite was employed to remove U(VI) at different experimental conditions. The influence of solid/liquid ratio, contact time, pH, ionic strength, humic substances and temperature on sorption of U(VI) to NKF-6 zeolite was investigated using batch technique under ambient conditions. The experimental results demonstrated that the sorption of U(VI) on NKF-6 zeolite was strongly dependent on pH. The sorption property of U(VI) was influenced by ionic strength at pH < 7.0, whereas was independent of ionic strength at pH > 7.0. The presence of fulvic acid or humic acid promoted the sorption of U(VI) on NKF-6 zeolite at low pH values while restrained the sorption at high pH values. The thermodynamic parameters (i.e., ΔS ⁰, ΔH ⁰, and ΔG ⁰) calculated from the temperature-dependent sorption isotherms demonstrated that the sorption process of U(VI) on NKF-6 zeolite was endothermic and spontaneous. At low pH values, the sorption of U(VI) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on NKF-6 zeolite surfaces, while inner-sphere surface complexation was the main sorption mechanism at high pH values. From the experimental results, one can conclude that NKF-6 zeolite can be used as a potential adsorbent for the preconcentration and solidification of U(VI) from large volumes of aqueous solutions.     

A high efficient sorption of U(VI) from aqueous solution using amino-functionalized SBA-15

Uranium is one of the most hazardous heavy metal due to its long half-life radioactivity, high toxicity and mobility as aqueous uranyl ion (UO₂ ²⁺) under ordinary environmental conditions. Herein, amino functionalized SBA-15 (APSS) was developed as a rapid and efficient sorbent for removal of U(VI) from the environment. The APSS sample was synthesized by grafting method and was characterized by SEM, NMR, SAXS, and N₂ sorption/desorption isothermal experiments. The sorption of U(VI) by APSS was investigated under different conditions of pH, contact time, initial U(VI) concentration, ionic strength and solid–liquid ratio. The results show that the sorption of U(VI) by APSS is strongly dependent on pH but independent of ionic strength and solid–liquid ratios (m/V). The sorption is ultrafast with an equilibrium time of less than 30 min, and the sorption capacity is as large as 409 mg/g at pH 5.3 ± 0.1. Besides, the U(VI) sorption by APSS from extremely diluted solution and the desorption of U(VI) from APSS were also studied. It is found that 100 mg of APSS can almost completely remove the U(VI) ions from 4 L aqueous solution with the U(VI) concentration as low as 4.2 ppb and the sorbed U(VI) can be completely desorbed by 0.1 mol/L nitric acid. The results strongly reveal the high performance of the APSS material in the removal and preconcentration of U(VI) from the aqueous solution.     

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

Silica gel surface was chemically functionalized by reaction the silanol from the silica surface with 3-chloropropyltrimethoxysilane followed by reaction with Sulfasalazine. This new sorbent has been used for the preconcentration of low levels of U(VI) ions from an aqueous phase. Parameters involved in extraction efficiency such as pH, weight of the sorbent, volume of sample and eluent were optimized in batch and column methods prior to determination by spectrophotometry using arsenazo(III) reagent. The results showed that U(VI) ions can be sorbed at pH range of 5.0–6.0 in a minicolumn and quantitative recovery of U(VI) (>98.0?±?1.6%) was achieved by stripping with 2.5 mL of 0.1 mol L^?1 HCl. The sorption capacity of the functionalized silica gel was 1.15 mmol g^?1 of U(VI). A linear calibration graph was obtained over the concentration range of 0.02–27.0 μg mL^?1 with a limit of detection of 1 μg L^?1 in treatment with 1000 mL of the U(VI) solution in which the preconcentration factor was as high as 400. The method was employed to the preconcentration of U(VI) ions from spiked ground water and synthetic sea water samples.     

Interaction of U(VI) with Na-attapulgite in the presence and absence of humic acid as a function of pH, ionic strength and temperature

The interaction of U(VI) with Na-attapulgite was studied by using batch technique at different experimental conditions. The effect of contact time, solid content, pH, ionic strength and temperature on the sorption of U(VI) onto Na-attapulgite in the presence and absence of humic acid was also investigated. The results showed that the sorption of U(VI) on Na-attapulgite achieved sorption equilibrium quickly. Sorption of U(VI) on Na-attapulgite increased quickly with increasing pH at pH < 6.5, and then decreased with pH increasing at pH > 6.5. The sorption curves were shifted to left in low NaClO₄ solutions as compared those in high NaClO₄ solutions. The sorption was strongly dependent on pH and ionic strength. The sorption was dominated by ion exchange or outer-sphere surface complexation at low pH values, and by inner-sphere surface complexation or surface precipitation at high pH values. The thermodynamic parameters (i.e., ΔH ⁰, ΔS ⁰, and ΔG ⁰) for the sorption of U(VI) were calculated from the temperature dependent sorption isotherms, and the results suggested that the sorption reaction was an endothermic and spontaneous process. The Na-attapulgite is a suitable material in the removal and preconcentration of U(VI) from large volumes of aqueous solutions in nuclear waste management.     

Removal of U(VI) from aqueous solutions by using MWCNTs and chitosan modified MWCNTs

In this paper, the multiwalled carbon nanotubes (MWCNTs) were modified with chitosan (CS) by using low temperature plasma grafting technique (denoted as MWCNT-CS). The prepared MWCNTs and MWCNT-CS were characterized by SEM, TEM, FTIR and Raman spectroscopy in detail and the results suggested that CS molecules were successfully grafted on the surfaces of MWCNTs. The materials were applied as adsorbents in the removal of U(VI) ions from large volumes of aqueous solutions as a function of environmental conditions. The removal of U(VI) from aqueous solution to MWCNTs and MWCNT-CS increased with increasing pH values at pH < 7, and then decreased with increasing pH values at pH > 7. The sorption of U(VI) on MWCNTs and MWCNT-CS was strongly dependent on pH and independent of ionic strength. The sorption of U(VI) on MWCNTs and MWCNT-CS was dominated by inner-sphere surface complexation rather than by ion exchange or outer-sphere surface complexation. The surface grafted chitosan molecules can enhances U(VI) sorption on MWCNTs obviously, which was also evidenced from the XPS spectroscopy analysis. The results of high sorption capacity of U(VI) on MWCNT-CS suggest that the MWCNT-CS nanomaterial is a suitable candidate in the preconcentration of U(VI) ions from large volumes of aqueous solutions.     

Removal of uranium(VI) from aqueous solution using sponge iron

Direct reduced iron (DRI), also called sponge iron, was used for the removal of U(VI) from aqueous solution. Batch experiments were conducted to evaluate the effect of various factors including contact time, solution pH, DRI dosage and initial uranium concentration on this removal process. The result suggested that U(VI) can be rapidly removed by DRI and this removal process followed an apparent first-order reaction kinetics. The optimum pH for uranium removal was between 2.0 and 4.0. Whether U(VI) can be fully removed was influenced by the molar ratio of DRI to U(VI) in solution. The aqueous U(VI) can be removed completely when this ratio was more than ca. 1,000. The U(VI) removal capacities of DRI decreased with increasing DRI dosages at a constant concentration of U(VI), but increased almost linearly with increasing initial U(VI) concentrations at a fixed dosage of DRI. The maximum U(VI) removal capacity was 5.71 mg/g DRI. Finally, the possible mechanism of U(VI) removal by DRI was also discussed. The XPS and XRD analysis showed that U(VI) was deposited as UO₃ onto DRI surface, indicating that U(VI) can be removed without reduction.     

Removal of uranium from aqueous solution by using activated palm kernel shell carbon: adsorption equilibrium and kinetics

Activated palm kernel shell carbon (APKSC) was used to remove U(VI) from aqueous solutions in a batch system. The adsorption kinetics, isotherms, and effects of various parameters, such as temperature, contact time, solution pH, adsorbent dosage, and initial U(VI) concentration on the U(VI) adsorption process were studied. Equilibrium was reached after 120 min in the range of studied U(VI) concentrations and temperatures. U(VI) uptake was insignificantly affected by temperature, but was highly pH dependent, and the optimum pH for removal was 5.5. U(VI) removal efficiency increased with the increasing adsorbent dosage. U(VI) sorption capacity increased with increasing initial U(VI) concentration; any further increases in initial U(VI) concentration above a certain point caused insignificant changes in U(VI) sorption capacity. Isotherm data could be described by the Langmuir isotherm model with a maximum U(VI) adsorption capacity of 51.81 mg/g. Kinetic data were fitted to pseudo-first-order and pseudo-second-order equations, which suggested that the U(VI) adsorption onto APKSC was better reproduced by the pseudo-second-order model rather than pseudo-first-order model. Our results indicated that APKSC might be used as a cheap adsorbent in the treatment of uranium-containing wastewater.     

Preparation and sorption performance of magnetic 18-crown-6/Fe3O4 nanocomposite for uranium(VI) in solution

A new magnetic nanocomposite material, magnetic 18-crown-6/Fe₃O₄ nanocomposite (MCFN), was prepared for the removal of U(VI) from aqueous solution. The MCFN was composed of Fe₃O₄ nanoparticales modified by covalent attachment of 18-crown-6, which can help the material to be removed easily from solution by magnetic force. As a new adsorbent for U(VI) removal, MCFN was characterized by infrared radiation, scanning electron microscopy with energy dispersive X-ray spectroscopy, vibrating sample magnetometer and thermal gravimetric analysis. Those factors affecting the sorption behavior of U(VI), such as acidity, temperature, initial concentration of U(VI) and the amount of crown ethers were studied by orthogonal experiments. A maximum U(VI) sorption capacity of 91.12 mg g^?1 was achieved at 45 °C, pH 5.5 for 30 min. The experimental results showed that MCFN had great sorption capacity, high selectivity and strong potentiality of enrichment and recovery for U(VI). In summary, MCFN is a promising candidate for U(VI) separation in future practical applications.     

Biosorption behaviors of uranium (VI) from aqueous solution by sunflower straw and insights of binding mechanism

Uranium (VI)-containing water has been recognized as a potential longer-term radiological health hazard. In this work, the sorptive potential of sunflower straw for U (VI) from aqueous solution was investigated in detail, including the effect of initial solution pH, adsorbent dosage, temperature, contact time and initial U (VI) concentration. A dose of 2.0 g L^?1 of sunflower straw in an initial U (VI) concentration of 20 mg L^?1 with an initial pH of 5.0 and a contact time of 10 h resulted in the maximum U (VI) uptake (about 6.96 mg g^?1) at 298 K. The isotherm adsorption data was modeled best by the nonlinear Langmuir–Freundlich equation. The equilibrium sorption capacity of sunflower straw was observed to be approximately seven times higher than that of coconut-shell activated carbon as 251.52 and 32.37 mg g^?1 under optimal conditions, respectively. The positive enthalpy and negative free energy suggested the endothermic and spontaneous nature of sorption, respectively. The kinetic data conformed successfully to the pseudo-second-order equation. Furthermore, energy dispersive X-ray, fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy demonstrated that U (VI) adsorption onto sunflower straw was predominantly controlled by ion exchange as well as complexation mechanism. The study revealed that sunflower straw could be exploited for uranium remediation of aqueous streams as a promising adsorbent.     

Simultaneous spectrophotometric determination of uranium, nitric acid and nitrous acid by least-squares method in PUREX process

Multi-wavelength linear regression spectrophotometry combined with method of least squares for simultaneous determination of uranium, nitric acid and nitrous acid in PUREX (Plutonium/URanium EXtraction) process was developed. The molar absorbance matrix was calibrated with absorbance data measured in the wavelength range of 350–500 nm for a series of standard solutions by linear least-squares regression. This method used information from the absorption spectra of U(VI)–nitrous acid–nitric acid solutions to determine U(VI), nitrous acid and nitric acid. In the range of 0.95–74.1 g/L U(VI), 5 × 10^?4–2 × 10^?3 mol/L nitrous acid and 3–5 mol/L aqueous nitric acid solution, the measuring precision for determination of U(VI), nitrous acid and nitric acid was 0.46, 4.09, and 0.68 % respectively. In the solution of 30 % TBP–kerosene, the measuring precision for determination of U(VI) and nitrous acid was 0.42 and 4.2 % respectively in the range of 0.95–74.1 g/L U(VI) and 5 × 10^?4–2×10^?3 mol/L nitrous acid. The spectrophotometric method can be valuable for monitoring and controlling of both species in PUREX process operation, thanks to its simplicity, efficiency and accuracy.     

Biosorption of uranium(VI) by free and entrapped Chlamydomonas reinhardtii: kinetic,equilibrium and thermodynamic studies

Biosorption of uranium from aqueous solution onto the free and entrapped algae, “Chlamydomonas reinhardtii” in carboxymethyl cellulose (CMC) beads was investigated in a batch system using bare CMC beads as a control system. CMC can be a potential natural biosorbent for radionuclide removal as it contains carboxyl groups. However, limited information is available with the biosorption of uranium by CMC, when adsorption isotherm, kinetics and thermodynamics parameters are concerned. The biosorbent preparations were characterized by swelling tests, FTIR, and surface area studies. The effects of pH, temperature, ionic strength, biosorbent dosage, and initial uranium concentrations on uranium biosorption were investigated. Freely suspended algae exhibited the highest uranium uptake capacity with an initial uranium ion concentration of 1,000 mg/L at pH of 4.5 and at 25 °C. The removal of U(VI) ion from the aqueous solution with all the tested biosorbents increased as the initial concentration of U(VI) ion increased in the medium. Maximum biosorption capacities for free algal cells, entrapped algal cells, and bare CMC beads were found to be 337.2, 196.8, and 153.4 mg U(VI)/g, respectively. The kinetic studies indicated that the biosorption of U(VI) ion was well described by the pseudo-second order kinetic model. The variations in enthalpy and entropy for the tested biosorbent were calculated from the experimental data. The algal cells entrapped beads were regenerated using 10 mM HNO₃, with up to 94 % recovery. Algal cells entrapped CMC beads is a low cost and a potential composite biosorbent with high biosorption capacity for the removal of U(VI) from waters.     

Adsorption Behavior of U(VI) and Re(VII) on Iron Sulfide Nanoparticles Modified with Titanate Nanotubes: Mechanism and Performance Insights

A novel nanocomposite (TNTs-FeS) was developed by anchoring ferrous sulfide (FeS) nanoparticles immobilized on titanate nanotubes (TNTs) by hydrothermal method to remove U(VI) and Re(VII) from aqueous solution, and the removal mechanism and efficiency were examined. The experimental results showed that the TNTs can effectively improve the dispersibility and stability of FeS. The environmental conditions, including initial solution pH, initial concentration, equilibrium time, and dosage, played an important role in the remediation process, which can affect the immobilization efficiency significantly. The maximum quantity removal of U(VI) and Re(VII) was 291.67 and 226.23 mg/g at pH of 6.0 and 12.0. The adsorption kinetics and the equilibrium isotherms of U(VI) and Re(VII) all fitted well with the pseudo-second-order model (R²>0.99) and the Freundlich model (R²>0.99). The main mechanism of removal by TNTs-FeS was electrostatic attraction, chemical reduction, and surface complexation. Thus, TNTs-FeS composites exhibited a high potential to remove U(VI) and Re(VII) heavy metal ions from the surface and groundwater.     

Synthesis of phosphorus-modified poly(styrene-co-divinylbenzene) chelating resin and its adsorption properties of uranium(VI)

A new phosphorus-modified poly(styrene-co-divinylbenzene) chelating resin (PS–N–P) was synthesized by P,P-dichlorophenylphosphine oxide modified commercially available ammoniated polystyrene beads, and characterized by Fourier transform infrared spectroscopy and elemental analysis. The adsorption properties of PS–N–P toward U(VI) from aqueous solution were evaluated using batch adsorption method. The effects of the contact time, temperature, pH and initial uranium concentration on uranium(VI) uptake were investigated. The results show that the maximum adsorption capacity (97.60 mg/g) and the maximum adsorption rate (99.72 %) were observed at the pH 5.0 and 318 K with initial U(VI) concentration 100 mg/L and adsorbent dose 1 g/L. Adsorption equilibrium was achieved in approximately 4 h. Adsorption kinetics studied by pseudo second-order model stated that the adsorption was the rate-limiting step (chemisorption). U(VI) adsorption was found to barely decrease with the increase in ionic strength. Equilibrium data were best modeled by the Langmuir isotherm. The thermodynamic parameters such as ?G ₀, ?H ₀ and ?S ₀ were derived to predict the nature of adsorption. Adsorbed U(VI) ions on PS–N–P resin were desorbed effectively (about 99.39 %) by 5 % NaOH–10 % NaCl. The synthesized resin was suitable for repeated use.