Adsorption and thermodynamic behaviour of U(VI) on the Tendurek volcanic tuff

In this work, sorption of uranium ions on volcanic tuff collected from the deposits located at the Tendurek of Eastern Turkey was investigated in batch technique. The effect of different parameters such as pH of the medium, contact time, uranium concentration and temperature were investigated. The maximum removal of U(VI) was found to be 68% at pH 5.0, initial U(VI) concentration of 75 mg L⁻¹ and 30 °C. Thermodynamic parameters, such as enthalpy of adsorption ∆H°, free energy change ∆G° and entropy change ∆S° have been also calculated and interpreted. The suitability of the Langmuir, Freundlich and Dubinin-Radushkhevic adsorption models to the equilibrium data was investigated for uranium-volcanic tuff system. The results suggest that volcanic tuff can be used as efficient and cost effective adsorbents for uranium ion removal.     

Adsorption and thermodynamic behavior of uranium on natural zeolite

Adsorptive behavior of natural clinoptilolite-rich zeolite from Balikesir deposites in Turkey was assessed for the removal of uranium from aqueous solutions. The uranium uptake and cation exchange capacities of zeolite were determined. The effect of initial uranium concentrations in solution was studied in detail at the optimum conditions determined before (pH 2.0, contact time: 60 minutes, temperature: 20 °C). The uptake equilibrium is best described by Langmuir adsorption isotherm. Some thermodynamic parameters (ΔH°, ΔS°, ΔG°) of the adsorption system were also determined. Application to fixation of uranium to zeolite was performed. The uptake of uranium complex on zeolite followed Langmuir adsorption isotherm for the initial concentration (25 to 100 μg/ml). Thermodynamic values of ΔG°, ΔS° and ΔH° found show the spontaneous and exothermic nature of the process of uranium ions uptake by natural zeolite. This revised version was published online in August 2006 with corrections to the Cover Date.     

Adsorptive removal of uranium from aqueous solution using chitosan-coated attapulgite

Chitosan-coated attapulgite beads were prepared by coating chitosan on naturally and abundantly available attapulgite, and made into spherical beads to adsorb uranium from aqueous solutions. The beads were characterized by SEM, EDS and FT-IR. The characteristics of beads of adsorbing uranium(VI) from aqueous solutions were studied at different conditions of pH, initial uranium concentration, contact time, biomass dosage and temperature. The pseudo-second order rate equation was used to describe the kinetic data, and isotherm data were fitted to Langmuir and Freundlich adsorption models. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°) of the biosorption were also calculated. Thermodynamic parameters of the CAAB, viz., ΔG°(308 K), ΔH°, and ΔS° were determined to be −21.59, 6.29l and 90.51 J/mol K, respectively. The experimental results demonstrate that the beads of chitosan coated onto attapulgite exhibit considerable potential for application in both adsorption and removal of uranium from aqueous solutions.     

Diglycolamide functionalized multi-walled carbon nanotubes for removal of uranium from aqueous solution by adsorption

Diglycolamide functionalized multi-walled carbon nanotubes (DGA-MWCNTs) were synthesized by sequential chemical reactions for removal of uranium from aqueous solution. Characterization studies were carried out using FT-IR spectroscopy, XRD and SEM analysis. Adsorption of uranium from aqueous solution on this material was studied as a function of nitric acid concentration, adsorbent dose and initial uranium concentration. The uranium adsorption data on DGA-MWCNTs followed the Langmuir and Freundlich adsorption isotherms. The adsorption capacity of DGA-MWCNTs as well as adsorption isotherms and the effect of temperature on uranium ion adsorption were investigated. The standard enthalpy, entropy, and free energy of adsorption of the uranium with DGA-MWCNTs were calculated to be 6.09 kJ mole⁻¹, 0.106 kJ mole⁻¹ K⁻¹ and −25.51 kJ mole⁻¹ respectively at 298K. The results suggest that DGA-MWCNTs can be used as efficient adsorbent for uranium ion removal.     

Adsorption of uranium from crude phosphoric acid using activated carbon

The adsorption of uranium from crude phosphoric acid has been investigated using conventional activated carbons. It was found that treatment with nitric acid oxidized the surface of activated carbon and significantly increased the adsorption capacity for uranium in acidic solutions. The parameters that affect the uranium(VI) adsorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated. Equilibrium data were fitted to a simplified Langmuir and Freundlich isotherms for the oxidized samples which indicate that the uranium adsorption onto the activated carbon fitted well with Langmuir isotherm than Freundlich isotherm. Equilibrium studies evaluate the theoretical capacity of activated carbon to be 45.24 g kg^?1.     

Biosorption of uranium(VI) by a mangrove endophytic fungus <Emphasis Type="Italic">Fusarium sp</Emphasis>. #ZZF51 from the South China Sea

The uranium(VI) accumulation was studied in detail by using the biomass of mangrove endophytic fungus Fusarium sp.#ZZF51 from the South China Sea. The uranium(VI) biosorption process onto the tested fungus powders was optimized at pH 4.0, adsorption time 60 min, and uranium(VI) initial concentration 50 mg L⁻¹ with 61.89% of removal efficiency. According to Fourier transform infrared spectra for the tested fungus before and after loaded with uranium(VI), the results showed that both of hydroxyl and carboxyl groups acted as the important roles in the adsorption process. In addition, the experimental data were analyzed by using parameter and kinetic models, and it was obtained that the Langmuir isotherm model and the pseudo-second-order kinetic model provided better correlation with the experimental data for adsorption of uranium(VI).     

Adsorption of uranium ions by crosslinked polyester resin functionalized with acrylic acid from aqueous solutions

In this paper, the crosslinked polyester resin containing acrylic acid functional groups was used for the adsorption of uranium ions from aqueous solutions. For this purpose, the crosslinked polyester resin of unsaturated polyester in styrene monomer (Polipol 353, Poliya) and acrylic acid as weight percentage at 80 and 20%, respectively was synthesized by using methyl ethyl ketone peroxide (MEK_p, Butanox M60, Azo Nobel)-cobalt octoate initiator system. The adsorption of uranium ions on the sample (0.05 g copolymer and 5 mL of U(VI) solution were mixed) of the crosslinked polyester resin functionalized with acrylic acid was carried out in a batch reactor. The effects of adsorption parameters of the contact time, temperature, pH of solution and initial uranium(VI) concentration for U(VI) adsorption on the crosslinked polyester resin functionalized with acrylic acid were investigated. The adsorption data obtained from experimental results depending on the initial U(VI) concentration were analyzed by the Freundlich, Langmuir and Dubinin–Radushkevich (D–R) adsorption isotherms. The adsorption capacity and free energy change were determined by using D–R isotherm. The obtained experimental adsorption data depending on temperature were evaluated to calculate the thermodynamic parameters of enthalpy (ΔH°), entropy (ΔS°) and free energy change (ΔG°) for the U(VI) adsorption on the crosslinked polyester resin functionalized with acrylic acid from aqueous solutions. The obtained adsorption data depending on contact time were analyzed by using adsorption models such as the modified Freundlich, Elovich, pseudo-first order and pseudo-second-order kinetic models.     

Adsorption characteristics of uranyl ions by manganese oxide coated sand in batch mode

In this paper, the sorption properties of manganese oxide coated sand (MOCS) towards uranium(VI) from aqueous solutions were studied in a batch adsorption system. Scanning electron microscope (SEM) and infrared (IR) analyses were used to characterize MOCS. Parameters affecting the adsorption of uranium(VI), such as the contact time, salt concentration, competitive ions, temperature and initial uranium(VI) concentration, were investigated. The equilibrium adsorption data were analyzed by Langmuir, Freundlich and Redlich–Peterson models using nonlinear regressive analysis. The results indicated that the Langmuir and Redlich–Peterson models provided the best correlation of experimental data. The kinetic experimental data were analyzed using three kinetic equations including pseudo-first order equation, pseudo-second order equation and intraparticle diffusion model to examine the mechanism of adsorption and potential rate-controlling step. The process mechanism was found to be complex, consisting of both surface adsorption and pore diffusion. The effective diffusion parameter D _i values estimated in the order of 10⁻⁷ cm² s⁻¹ indicated that the intraparticle diffusion was not the rate-controlling step. Thermodynamic study showed that the adsorption was a spontaneous, endothermic process. Adsorbed U(VI) ions were desorbed effectively (about 94.7%) by 0.1 mol L⁻¹ HNO₃. The results indicated that MOCS can be used as an effective adsorbent for the treatment of industrial wastewaters contaminated with U(VI) ions.     

Biosorption of Cadmium,Lead, and Uranium by Powder of Poplar Leaves and Branches

The removal of metal ions from aqueous solutions by biosorption plays an important role in water pollution control. In this study, dried leaves and branches of poplar trees were studied for removing some toxic elements (cadmium, lead, and uranium) from aqueous solutions. The equilibrium experiments were systematically carried out in a batch process, covering various process parameters that include agitation time, adsorbent size and dosage, initial cadmium, lead and uranium concentration, and pH of the aqueous solution. Adsorption behavior was found to follow Freundlich and Langmuir isotherms. The results have shown that both dried leaves and branches can be effectively used for removing uranium, while only branches were found to remove lead and cadmium completely from the aqueous solution. The maximum biosorption capacity of leaves for uranium was found to be 2.3 mg g⁻¹ and 1.7 mg g⁻¹ and 2.1 mg g⁻¹ for lead and cadmium on branches, respectively. In addition, the studied biomass materials were used in removing lead and cadmium from contaminated water and the method was found to be effective.     

Uranium removal from aqueous solutions by wood powder and wheat straw

The influence of initial uranium concentration, solution pH, contact time and adsorbent mass was investigated for removal of uranium from aqueous solutions by pine wood powder and wheat straw using a batch technique. The maximum removal efficiency of uranium achieved at pH 8 and 7 for pine wood powder and wheat straw, respectively. Langmuir and Freundlich adsorption isotherms and three kinetic models of adsorption including; Elovich, Lagergren pseudo-first and Lagergren pseudo-second order were used to describe the adsorption mechanisms. The uranium sorption onto wood and wheat straw powders followed a Freundlich isotherm. The kinetic studies showed that the data fitted very well to the pseudo-second order model in the studied concentration range of uranium for both adsorbents. Uranium desorption from loaded adsorbents also studied using batch techniques as a function of desorptive reagent, desorption time and desorptive reagent concentration. The results of the experiment indicated that the optimum desorption efficiency of uranium for wood powder and wheat straw occurred in 5 min shaking time, using 1.5 M HNO₃ and 2 M Na₂CO₃ solutions, respectively.     

Removal of uranium(VI) from acetate medium using Lewatit TP 260 resin

Removal of uranium(VI) ions from acetate medium in aqueous solution was investigated using Lewatit TP260 (weakly acidic, macroporous-type ion exchange resin with chelating aminomethylphosphonic functional groups) in batch system. The parameters that affect the uranium(VI) sorption, such as contact time, solution pH, initial uranium(VI) concentration, adsorbent dose and temperature have been investigated. Results have been analyzed by Langmuir and Freundlich isotherm; the former was more suitable to describe the sorption process. The moving boundary particle diffusion model only fits the initial metal adsorption on the resin. The rate constant for the uranium sorption by Lewatit TP260 was 0.441 min⁻¹ from the first order rate equation. The total sorption capacity was found to be 58.33 mg g⁻¹ under optimum experimental conditions. Thermodynamic parameters (ΔH = 61.74 kJ/mol; ΔS = 215.3 J/mol K; ΔG = −2.856 kJ/mol) showed the adsorption of an endothermic process and spontaneous nature, respectively.     

Binary biosorption of uranium(VI) and nickel(II) from aqueous solution by Ca-pretreated Cystoseira indica in a fixed-bed column

Simultaneous biosorption of uranium(VI) and nickel(II) ions onto Ca-pretreated Cystoseira indica biomass was studied and compared with single uranium or nickel biosorption in a fixed-bed column. Results of single biosorption showed the breakthrough and exhaustion time increase with the increase of the flow rate and inlet metal concentration for both metal ions. Also, it was observed that there was an optimum flow rate of 1.4 mL min⁻¹ (surface loading of 0.792 cm min⁻¹) for both metal ions in the column. Results from both single and binary systems showed the adsorption capacity of C. indica for both metal ions increases with the increasing inlet concentration of each component and C. indica had a stronger affinity for uranium than nickel ions. The binary system results showed that the presence of the second component affected the adsorption of the first one by C. indica so the antagonistic action was observed. Also, the inhibitory effect of uranium ions on the nickel adsorption was greater than nickel ions on the uranium adsorption. The uranium and nickel breakthrough curves under different conditions were described by the Thomas, Yoon-Nelson and Yan models. Among these models, the Yan model appeared to describe the experimental results better.     

Adsorption of uranium(VI) onto <Emphasis Type="Italic">Ulva sp.</Emphasis>-sepiolite composite

Ulva sp. and sepiolite were used to prepare composite adsorbent. The adsorption of uranium(VI) from aqueous solutions onto Ulva sp.-sepiolite has been studied by using a batch adsorber. The parameters that affect the uranium(VI) adsorption, such as solution pH, initial uranium(VI) concentration, and temperature, have been investigated and the optimum conditions determined. The adsorption patterns of uranium on the composite adsorbent followed the Freundlich and Dubinin-Radushkevich (D-R) isotherms. The Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) models have been applied and the data correlate well with Freundlich model. The sorption is physical in nature (sorption energy, E = 4.01 kJ/mol). The thermodynamic parameters such as variation of enthalpy ΔH, variation of entropy ΔS and variation of Gibbs free energy ΔG were calculated from the slope and intercept of lnK _d vs. 1/T plots. Thermodynamic parameters (ΔH _ads = −22.17 kJ/mol, ΔS _ads = −17.47 J/mol·K, ΔG ^o _ads (298.15 K) = −16.96 kJ/mol) show the exothermic heat of adsorption and the feasibility of the process. The results suggested that the Ulva sp-sepiolite composite adsorbent is suitable as a sorbent material for recovery and biosorption/adsorption of uranium ions from aqueous solutions.     

Effect of complexants on the adsorption and color reactions of lanthanum(III), uranium(VI), thorium(IV), and zirconium(IV) with Arsenazo M in the solid phase of an ANKB-50 fibrous ion-exchanger

The effect of complexants—acetic, aminoacetic, tartaric, malonic, and oxalic acids; EDTA; and Na₂CO₃—on the adsorption and subsequent determination of thorium(IV), lanthanum(III), uranium(VI), and zirconium(IV) with Arsenazo M in the solid phase of polyacrylonitrile fiber filled with an ANKB-50 anion exchanger was studied. Complexing agents were introduced into the solution at the step of metal ion adsorption. It was shown that zirconium and uranium interacted with the iminodiacetate groups of the adsorbent in the course of adsorption; the adsorption of elements from 10^?3 to 10^?2 M complexant solutions (except for tartaric and oxalic acids and EDTA) under the optimum conditions was enhanced as compared to their adsorption from pure solutions; complexation with Arsenazo M in the solid phase proceeded at a higher acidity than in the solution. When the elements were present simultaneously, their total concentration and individual thorium could be determined from malonic acid solutions with Arsenazo M by varying the concentration of acid and the adsorption pH.     

Efficient uranium(VI) biosorption on grapefruit peel: kinetic study and thermodynamic parameters

The uranium(VI) biosorption by grapefruit peel was studied from aqueous solutions. Batch experiments was conducted to evaluate the effect of contact time, initial uranium(VI) concentration, initial pH, adsorbent dose, salt concentration and temperature. The equilibrium process was well described by the Langmuir, Redlich–Peterson and Koble–Corrigan isotherm models, with maximum sorption capacity of 140.79 mg g⁻¹ at 298 K. The pseudo second order model and Elovish model adequately describe the kinetic data in comparison to the pseudo first order model and the process involving rate-controlling step is much complex involving both boundary layer and intra-particle diffusion processes. The effective diffusion parameter D _i and D _f values were estimated at different initial concentration and the average values were determined to be 1.167 × 10⁻⁷ and 4.078 × 10⁻⁸ cm² s⁻¹. Thermodynamic parameters showed that the biosorption of uranium(VI) onto grapefruit peel biomass was feasible, spontaneous and endothermic under studied conditions. The physical and chemical properties of the adsorbent were determined by SEM, TG-DSC, XRD and elemental analysis and the nature of biomass–uranium (VI) interactions was evaluated by FTIR analysis, which showed the participation of COOH, OH and NH₂ groups in the biosorption process. Adsorbents could be regenerated using 0.05 mol L⁻¹ HCl solution at least three cycles, with up to 80% recovery. Thus, the biomass used in this work proved to be effective materials for the treatment of uranium (VI) bearing aqueous solutions.     

Preparation of carbon coated Fe3O4 nanoparticles for magnetic separation of uranium

Uranium(VI) was removed from aqueous solutions using carbon coated Fe₃O₄ nanoparticles (Fe₃O₄@C). Batch experiments were conducted to study the effects of initial pH, shaking time and temperature on uranium sorption efficiency. It was found that the maximum adsorption capacity of the Fe₃O₄@C toward uranium(VI) was ∼120.20 mg g⁻¹ when the initial uranium(VI) concentration was 100 mg L⁻¹, displaying a high efficiency for the removal of uranium(VI) ions. Kinetics of the uranium(VI) removal is found to follow pseudo-second-order rate equation. In addition, the uranium(VI)-loaded Fe₃O₄@C nanoparticles can be recovered easily from aqueous solution by magnetic separation and regenerated by acid treatment. Present study suggested that magnetic Fe₃O₄@C composite particles can be used as an effective and recyclable adsorbent for the removal of uranium(VI) from aqueous solutions.     

Adsorption kinetics of an organic dye by wet hybrid gel monoliths

Wet hybrid gel monoliths are prepared with bis(trimethoxysilylpropyl)amine (TSPA) or the mixture of TSPA with n-propyltriethoxysilane (PTES) or bis(trimethoxysilyl)hexane (TSH) or tetraethoxysilane (TEOS) as precursors. The adsorption kinetics of an organic dye (erioglaucine disodium salt, EDS) by the gel monoliths in aqueous solutions is studied comprehensively. The effects of temperature, pH, and ionic strength on the adsorption kinetics are investigated. Kinetic studies show that in general the kinetic data are well described by the pseudo second-order kinetic model. Initial adsorption rate increases with the increase in temperature, but decreases with the increase in solution pH and ionic strength. The adsorption activation energy is found to be 17–51 kJ mol⁻¹ under our experimental conditions. The internal diffusion of the dye into the hybrid gels appears to be the rate-limiting step of the overall adsorption process. The adsorption is promoted by hydrogen bonding, hydrophobic and electrostatic attractions in acidic or neutral solutions, suppressed by the electrostatic repulsion in basic solutions and by the ionic exchange competition of Cl⁻ with the dye anions in solutions with a high NaCl concentration. After adsorption for 165 h, all the gel monoliths present a linear shrinkage less than 10%.     

Sorption of uranium by non-living water hyacinth roots

Summary Many studies have shown that water hyacinth (Eichhornia crassipes) roots can be used to accumulate high concentrations of organic as well as inorganic pollutants. They are currently used to remediate aquatic environments and aqueous solutions. In the present study, sorption of uranium from aqueous solutions by using dried roots of water hyacinth has been investigated. The sorption of uranium was examined as a function of initial concentration, pH, weight of roots and contact time. Five different concentrations 20, 40, 60, 80, and 100 μg ^. ml^-1 were used. Sorption proves to be very rapid and depend on pH, weight of roots and concentration of uranium. Maximum sorption capacity of water hyacinth roots was 64,000 U⁶⁺ μg/g. The sorption of uranium by water hyacinth roots follows a Langmuir isotherm.     

Adsorption behaviour of some actinides on zirconium phosphate stability constant determinations

The adsorption behaviour of thorium, protactinium, uranium, neptonium and plutonium on zirconium phosphate from nitric acid and ammonium nitrate solutions was investigated. Partition data from the mentioned media together with that from chloride solutions were used to calculate formation constants for the concerned elements in the range of Cl⁻ and NO ₃ ⁻ activities <1M. Obtained β values were compared with those reported in the literature and indicated reasonable agreement.     

Uranium adsorption characteristic and thermodynamic behavior of clinoptilolite zeolite

Summary Natural zeolite, clinoptilolite was tested for its ability to remove uranium from aqueous solutions. Influence parameters to the sorption process, such as initial uranium concentration, pH, contact time and temperature were investigated. Distribution coefficients of uranium on clinoptilolite were measured by batch technique. Experimental isotherms evaluated from the distribution coefficients were fit to Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models. Values of ΔH and ΔS were found as 0.93 and 56.09 J/mole, respectively. It was observed that the adsorption process is endothermic. Kinetics of uranium sorption was investigated at different time intervals at 30 °C. The reaction rate and diffusion constant were calculated.