Biosorption studies of uranium (VI) on cross-linked chitosan: isotherm,kinetic and thermodynamic aspects

The cross-linked chitosan (CS) gels synthesized by using glutaraldehyde (GLA), epichlorohydrin (EC), and ethylene glycol diglycidyl ether (EGDE) as cross-linkers respectively were used to investigate the adsorption of U(VI) ions in an aqueous solution. The pure chitosan (PCS) and the cross-linked chitosan gels were characterized by FTIR and SEM analysis. The kinetic, thermodynamic adsorption and adsorption isotherms of U(VI) ions onto unmodified and modified cross-linked chitosan were studied in a batch adsorption experiments. The effect of pH, contact time and temperature on the adsorption capacity were also carried out. At the optimum pH, the maximum adsorbed amount of PCS, GLACS, ECCS and EGDECS were 483.05, 147.05, 344.83 and 67.56 mg/g, respectively. The uranium (VI) adsorption process of PCS and ECCS followed better with pseudo-second-order kinetic model, while GLACS and EGDECS followed pseudo-first-order kinetic model well. The results obtained from the equilibrium isotherms adsorption studied of U(VI) ions were analyzed in two adsorption models, namely, Langmuir and Freundlich isothms models, the results showed that the Langmuir isotherm had better conformity to the equilibrium data. The thermodynamic parameters such as enthalpy (ΔHo), entropy (ΔSo), and Gibbs free energy (ΔGo) showed that the adsorption process was both spontaneous and endothermic.     

Removal of uranium(VI) and thorium(IV) ions from aqueous solutions by functionalized silica: kinetic and thermodynamic studies

Adsorption behavior of uranyl and thorium ions from synthetic radioactive solutions onto functionalized silica as sorbent has been investigated. The effect of contact time, initial concentration of radioactive solutions, sorbent mass, pH value and temperature on the adsorption capacity of the sorbent was investigated. Negative values of Gibbs free energy of adsorption suggested the spontaneity of the adsorption process on both functionalized silica with –NH₂ groups and with –SH groups. Positive values obtained for ΔH° indicates that the adsorption is an endothermic process. The adsorption isotherms were better fitted by Freundlich model and the adsorption kinetic was well described by the pseudo-second order equation. Desorption studies indicated that the most favorable desorptive reagents for UO₂ ²⁺ is HNO₃ 1 M and for Th⁴⁺ is EDTA 1 M solutions.     

Uranium(VI) recovery from its leach liquor using zirconium molybdophosphate composite: kinetic,equilibrium and thermodynamic studies

Journal of Radioanalytical and Nuclear Chemistry - A zirconium molybdophosphate composite was designed for the selective recovery of uranium ions. The synthesized composite was well-characterized...     

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.     

Biosorption of uranium(VI) from aqueous solution by Citrus limon peels: kinetics,equlibrium and batch studies

Citrus limon peel (exocarp) was chemically treated and used for removal of U(VI) ions from aqueous solution in a batch system. Optimization of U(VI) sorption parameters, i.e. medium pH, adsorbent amount, contact time, initial U(VI) ions concentration and temperature on the removal performance of both native and modified peels was studied. Adsorption capacity of the modified peel was near up to 4 times higher than of unmodified. The correlation regression coefficients show that the adsorption process can be well-defined by Langmuir equation. Additionally, it conforms to the pseudo-second order kinetic and Weber–Morris diffussion models well.

     

Biosorption of Cr(VI) ions from aqueous solutions: kinetics, equilibrium, thermodynamics and desorption studies

Cr(VI) is a major water pollutant from industrial effluent whose concentration is to be reduced within the permissible limit. Present study reports a systematic evaluation of six different natural adsorbents for the removal of Cr(VI) from aqueous solutions in batch process. The adsorption kinetic data were best described by pseudo-second order model. The values of mass transfer coefficient for Cr(VI) adsorption indicated that the velocity of the adsorbate transport from the bulk to the solid phase was quite fast. The effective diffusivity of Cr(VI) removal for all the adsorbents were of the order of 10(-10) m(2)/s which suggested chemisorption of the process. The adsorption process was jointly controlled by film diffusion and intraparticle diffusion. Maximum monolayer adsorption capacities onto the natural adsorbents used were comparable to the other natural adsorbents used by other researchers. The thermodynamic studies and sorption energy calculation using Dubinin-Radushkevich isotherm model indicated that the adsorption processes were endothermic and chemical in nature. FT-IR studies were carried out to understand the type of functional groups responsible for Cr(VI) binding process. Desorption study was carried out with different concentration of NaOH solutions. Application study was carried out using electroplating industrial wastewater.     

Synthesis, characterization, thermodynamic and kinetic investigations on uranium (VI) adsorption using organic-inorganic composites: Zirconyl-molybdopyrophosphate-tributyl phosphate

Zirconyl-molybdopyrophosphate-tributyl phosphate (ZMPP-TBP) was a novel organic-inorganic composite adsorbent prepared by co-precipitation method and used in the adsorption of uranium from aqueous solution in batch adsorption experiments. The as-obtained product was characterized using SEM, energy dispersive X-ray spectroscopy (EDX), XRD and BET-N₂ adsorption measurements. The study had been conducted to investigate the effects of solution pH, temperature, contact time, initial concentration and coexisting ions. A maximum removal of 99.31% was observed for an initial concentration 5 mg/L, at pH 6.0 and an adsorbent dose of 1.0 g/L. The isothermal data were fitted with both Langmuir and Freundlich equations, but the data fitted the former better than the latter. According to the evaluation using the Langmuir equation, the maximum adsorption capacity of uranium (VI) was 196.08 mg/g at 293 K and pH 6.0. The pseudo-first-order kinetic model and pseudo-second-order kinetic model were used to describe the kinetic data, and the pseudo-second-order kinetic model was better. The thermodynamic parameter ΔG was calculated, the negative ΔG values of uranium (VI) at different temperature showed that the adsorption process was spontaneous. The good reusability of ZMPP-TBP also indicated that the ZMPP-TBP was a very promising adsorbent for uranium adsorption from aqueous solution.     

The removal of uranium(VI) from aqueous solutions onto activated carbon: kinetic and thermodynamic investigations

The adsorption of uranium(VI) from aqueous solutions onto activated carbon has been studied using a batch adsorber. The parameters that affect the uranium(VI) adsorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated and optimized conditions determined (contact time 240 min; pH 3.0+/-0.1; initial uranium concentration 100 mg/L; temperature 293.15 K). The experimental data were analyzed using sorption kinetic models (pseudo-first- and pseudo-second-order equations) to determine the equation that fits best our experimental results. Equilibrium isotherm studies were used to evaluate the maximum sorption capacity of activated carbon and experimental results showed this to be 28.30 mg/g. The Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) models have been applied and the data correlate well with Freundlich model and that the sorption is physical in nature (the activation energy Ea=7.91 kJ/mol). Thermodynamic parameters (DeltaHads0=-50.53 kJ/mol, DeltaSads0=-98.76 J/mol K, DeltaGads(293.15 K)0=-21.61 kJ/mol) showed the exothermic heat of adsorption and the feasibility of the process.     

Biosorption characteristics of uranium(VI) from aqueous solution by pummelo peel

The biomass pummelo peel was chosen as a biosorbent for removal of uranium(VI) from aqueous solution. The feasibility of adsorption of U(VI) by Pummelo peel was studied with batch adsorption experiments. The effects of contact time, biosorbent dosage and pH on adsorption capacity were investigated in detail. The pummelo peel exhibited the highest U(VI) sorption capacity 270.71?mg/g at an initial pH of 5.5, concentration of 50???g/mL, temperature 303?K and contacting time 7?h. The adsorption process of U(VI) was found to follow the pseudo-second-order kinetic equation. The adsorption isotherm study indicated that it followed both the Langmuir adsorption isotherm and the Freundlich adsorption isotherm. The thermodynamic parameters values calculated clearly indicated that the adsorption process was feasible, spontaneous and endothermic in nature. These properties show that the pummelo peel has potential application in the removal of the uranium(VI) from the radioactive waste water.     

Effective adsorption of U(VI) from aqueous solution using magnetic chitosan nanoparticles grafted with maleic anhydride: equilibrium,kinetic and thermodynamic studies

The in situ formed magnetite nanoparticles was encapsulated by maleated chitosan to synthesize a novel magnetic chitosan nano-sorbent (MCN-MA) for the effective sorption of uranium. The sorption kinetics could be described by the pseudo-second-order model, whereas the sorption isotherms could be fitted to the Langmuir model (q _m = 187.9 mg/g). The MCN-MA showed higher U(VI) sorption capacities (compared to MCN) due to high affinity of carboxylate groups introduced from grafting maleic anhydride. Thermodynamic parameters indicate that U(VI) sorption is endothermic and feasible. The nano-size and magnetic property of the MCN-MA allow its efficient U(VI) sorption and facile magnetic separation from wastewaters.     

Chromium (III) removal by microporous ion exchanger Amberlite.120 (Na+): kinetic, equilibrium and thermodynamic studies

Cr (III) sorption on microporous strong cation exchanger Amberlite.120 (Na⁺) is studied as a function of time and temperature. The pH changes show the co-sorption of H⁺ ions along with the chromium. The rate constant values for Cr (III) sorption are calculated for both film and particle diffusion processes. However, the particle diffusion is found to be more dominant than the film diffusion. The temperature is found to have a positive effect on both the diffusional processes. The low values of energy of activation also confirm the diffusional nature of the process. Equilibrium data are explained with the help of Langmuir equation. Various thermodynamic parameters (??H, ??S and ??G) for Cr (III) exchange on the resin are calculated. The ??G values are found to be negative, while both the ??H and ??S values obtained are positive.     

Biosorption of Cd(II), Cr(III), and Cr(VI) by saltbush (Atriplex canescens) biomass: thermodynamic and isotherm studies

The biosorption data of Cd(II), Cr(III), and Cr(VI) by saltbush leaves biomass were fit on the Freundlich and Langmuir adsorption isotherms at 297 K. The Cd(II) and Cr(III) solutions were adjusted to pH 5.0 and the Cr(VI) solution was adjusted to pH 2.0. The correlation coefficient values indicated that the data fit better the Freundlich model. The maximal capacities (K(F)) were found to be 5.79 x 10(-2), 3.25 x 10(-2), and 1.14 x 10(-2) mol/g for Cr(III), Cd(II), and Cr(VI), respectively. Similar results were obtained using the Langmuir and the Dubinin-Radushkevick equations. Thermodynamic parameters calculated from the Khan and Singh equation and from the q(e) vs C(e) plot show that the equilibrium constants for the biosorption of the metals follow the same order of the maximal capacities. The negative Gibbs free energy values obtained for Cd(II) and Cr(III) indicated that these ions were biosorbed spontaneously. The mean free energy values calculated from the Dubinin-Radushkevick equation (10.78, 9.45, and 9.05 for Cr(III), Cr(VI), and Cd(II), respectively) suggest that the binding of Cd(II), Cr(III), and Cr(VI) by saltbush leaves biomass occurs through an ionic exchange mechanism.     

Complexation of uranium(VI) by salicylate and substituted salicylates: A kinetic study

Summary Kinetic studies on the complexation of uranium(VI) by salicylate and various substituted salicylates have been carried out using the stopped-flow spectrophotometric technique at pH 7.0–8.5 (NH₄OH+NH₄NO₃ buffer). Results are in conformity with a mechanism involving binding of UO₂OH⁺ species through the carboxylate group of the salicylate to form an inner-sphere species in a fast equilibrium (equilibrium constant=K) followed by a slow rate-determining ring closure (rate constant=k) involving loss of a molecule of water between the OH group bound to uranium(VI) and the phenolic group of the salicylate. The value of the equilibrium constant (K) obtained from the kinetic data in the case of 5-sulphosalicylate (log K=3.21 at 25 °C, I=1 M) is compatible with the literature thermodynamic value (log K = 3.89 at 25 °C, I=0.015 M). Increase in pH retards the reaction due to the equilibrium, UO₂OH⁺ + OH^– UO₂(OH)₂, the UO₂(OH)₂ being unreactive. The average value of K (log K=8.58 at 25°C, I=1M) obtained kinetically from the results of investigation with different ligands is also in good agreement with the literature thermodynamic value (log K= 8.8 at 25°C, I=0.1M). Both K and k are sensitive to the nature of the substituent in the benzene ring, decreasing with increasing acidity of the -CO₂H group of the salicyclic acid; the substituent effect is well demonstrated by the plot of log kversus _L (where ), which is linear. H^# and S^# values corresponding to k have been evaluated in each case. S^# values are all negative in conformity with ring closure in the rate-determining step.     

Uranium (VI) adsorption on synthesized 4A and P1 zeolites: Equilibrium,kinetic, and thermodynamic studies

The present work deals with the investigation of the use of synthesized 4A and P1 zeolites in the adsorption of uranium (VI) ions from liquid effluents (with initial concentrations of 100, 85 and 80 mg·L⁻¹). Batch experiments were performed and the effects of temperature, solid–liquid ratio, pH and initial UO₂²⁺ ion concentration were studied, and the optimal parameters were determined. The kinetic and thermodynamic aspects of the process as well as the diffusion mechanism have been studied. The obtained results showed that 4A and P1 zeolites are very effective adsorbents.     

Adsorption of U(VI) onto the carboxymethylated chitosan/Na-bentonite membranes: kinetic,isothermic and thermodynamic studies

The carboxymethylated chitosan (CMC)/Na-bentonite (Na-Bt) composite membranes were prepared and throughly characterized. The Na-Bt/CMC mass ratio was optimized, and CB10 (membrane with Na-Bt/CMC mass ratio of 10%) was selected as the best membrane for U(VI) sorption. XPS analysis indicates that the main mechanism for UO₂²⁺ sorption onto CB10 is through inner-surface complexation. The sorption kinetics followed pseudo-second order model, indicating the chemisorption as the rate-controlling step. The U(VI) sorption on CB10 is endothermic and spontaneous, with the maximum mono-layer adsorption capacity of 115.6 mg/g at pH 5.0 and 298 K. Finally, the U(VI)-loaded CB10 can consecutively desorbed and reused for several cycles.     

Effective uranium biosorption by macrofungus (<Emphasis Type="Italic">Russula sanguinea</Emphasis>) from aqueous solution: equilibrium,thermodynamic and kinetic studies

Russula sanguinea (R. sanguninea) macrofungus was employed as a novel cost-effective biosorbent for efficient removal of U(VI) ions from aqueous solution. FT-IR spectroscopy and SEM/EDS technique were used for morphological and chemical characterizations. The maximum adsorption capacity of the macrofungus was found as 174.3 mg/g at pH 5 and 20 °C. The kinetic data best fit with the pseudo-second-order kinetic model (r²?>?0.99 for the studied temperatures). The exothermic and spontaneous nature of the biosorption process was confirmed by the thermodynamic findings. The reusability test demonstrated that the macrofungus had a good sorption/desorption performance.     

The extraction equilibrium of uranium(VI) with i-butyldodecylsulfoxide (BDSO)

The i-butyldodecylsulfoxide (BDSO) was synthesized. The extraction of uranium(VI) has been carried out with BDSO in toluene from various HNO₃ concentrations. It was found that the distribution ratio increases with increasing nitric acid concentration up to 3.0 mol/l and then decreases. The distribution ratios also increase with increasing extractant concentration. The extracted species appears to be UO₂(NO₃)₂·2BDSO and the equilibrium constant value is 15.2. The influence of temperature, sodium nitrate and oxalate concentrations on the extraction was also investigated, and the thermodynamic functions of the extraction reaction were obtained.This revised version was published online in November 2005 with corrections to the Cover Date.     

Synergistic extraction and separation studies of uranium(VI)

A method is described for the extractive separation and spectrophotometric determination of uranium(VI) from an aqueous solution of pH 5.0–7.0 using benzoylacetone (bzac) and pyridine (py) dissolved in toluene as extractants. The extracted species are UO₂(bzac(₂·2py. The method provides separation of uranium(VI) from lanthanum(III), samarium(III), neodymium(III), cerium(III) and thorium(IV). The method is precise, accurate, fast and selective.     

Determination of the thermodynamic quantities of uranium(VI)–carboxylate complexes by microcalorimetry

Potentiometric and microcalorimetric titration techniques were applied for the determination of the Gibbs free energies and enthalpies of the protonation and U(VI) complexation of some carboxylic acids (formic, acetic, glycolic, and propionic acids) in 1.0 M NaClO₄ solution at 25 °C. By using the values of ΔG determined by potentiometric titrations, the results of calorimetric titrations were analyzed to give the values of ΔH and ΔS. These enthalpy values indicated that the protonation and uranyl(VI) complexation of these carboxylates were mainly entropy-driven, that is, ∣–TΔS∣ ≫ ∣ΔH∣ in ΔG = ΔH − TΔS. The comparison of TΔS_m values for uranyl acetate and glycolate complexation with those for europium(III) complexation revealed that the complexation of U(VI) was accompanied by larger entropy changes due to the limited space in its coordination sphere caused by the steric hindrance of two oxygens in the linear dioxo structure of uranyl ion.