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.     

Kinetics and mechanism of oxidation of ferrocyanide by N-bromosuccinimide in aqueous acidic solution

The kinetics of oxidation of ferrocyanide by N-bromosuccinimide (NBS) has been studied spectrophotometrically in aqueous acidic medium over temperature range 20–35 °C, pH = 2.8–4.3, and ionic strength = 0.10–0.50 mol dm⁻³ over a range of [Fe²⁺] and [NBS]. The reaction exhibited first order dependence on both reactants and increased with increasing pH, [NBS], and [Fe²⁺]. The rate of oxidation obeys the rate law: d[Fe³⁺]/dt = [Fe(CN)₆]^4–[HNBS⁺]/(k ₂ + k ₃/[H⁺]). An outer-sphere mechanism has been proposed for the oxidation pathway of both protonated and deprotonated ferrocyanide species. Addition of both succinimide and mercuric acetate to the reaction mixture has no effect on the reaction rate under the experimental conditions. Mercuric acetate was added to the reaction mixture to act as scavenger for any bromide formed to ensure that the oxidation is entirely due to NBS oxidation.     

Sorption of uranium complexes from aqueous solution

Summary The sorption of uranium-Arsenazo III complex was studied using Dowex-1x8 and carbonized apricot stone. The results show a similarity between the two sorbents since the percentage uptake of a uranium complex in the ratio 1 : 1 reaches 100% and 92% on the Dowex-1x8 and the carbonized apricot stone, respectively. Also the uptake of the complex on either sorbents increases with increasing the hydrogen ion concentration to reach a maximum value at pH 2.5. The two sorbents are used to study the sorption of uranium(VI) from seawater in the presence of 0.002% of Arsenazo III and 10^-3M EDTA, where it is found that uranium is completely sorbed by the two sorbents.     

Preparation and application of alginate-Ca/attapulgite clay core/shell particle for the removal of uranium from aqueous solution

The radioactivity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in 42 samples from different types of cements produced in Turkey were measured using gamma-ray spectrometer. The determined values were 18–143 Bq kg⁻¹ (²²⁶Ra), 5–66 Bq kg⁻¹ (²³²Th) and 142–540 Bq kg⁻¹ (⁴⁰K). Additionally, the calculated radiological hazard parameters such as absorbed dose rate, annual effective dose, radium equivalent activity, the external hazard, activity and alpha indices were found to be in the range of 38–158 nGy h⁻¹, 188–776 µSv year⁻¹, 41–182 Bq kg⁻¹, 0.11–0.49, 0.15–0.65 and 0.09–0.71, respectively. Finally, the results were statistically evaluated and compared with the reported data in other countries and the international standard values given by European Commission and UNSCEAR.

     

Low-cost reed straw-derived biochar prepared by hydrothermal carbonization for the removal of uranium(VI) from aqueous solution

Journal of Radioanalytical and Nuclear Chemistry - Uranium is the important nuclear fuel and its effective adsorption using low-cost materials is meaningful to environmental protection and...     

Rapid and efficient removal of Hg(II) from aqueous solution by potassium hexa-titanate: A radiotracer study

The adsorption of mercury(II) on potassium titanate has been studied in chloride media at different pH values, adsorbate concentrations and temperatures. Effect of different ligands and acid concentrations on the uptake was also investigated. Desoprtion studies were also done to check the reversibility of the process. Interestingly a more or less constant and high value of adsorption has been found at different temperatures, pH values and concentrations and a decrease in the uptake with an increase in the bulk acid concentration was observed.     

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.     

Diethylenetriamine functionalized silica gel for adsorption of uranium from aqueous solution and seawater

Journal of Radioanalytical and Nuclear Chemistry - The diethylenetriamine (DETA) organic moiety was anchored covalently on the surface of silica gel to obtain a surface-modified adsorbent...     

Geopolymeric adsorbents from fly ash for dye removal from aqueous solution

Adsorbents from coal fly ash treated by a solid-state fusion method using NaOH were prepared. It was found that amorphous aluminosilicate geopolymers would be formed. These fly ash-derived inorganic polymers were assessed as potential adsorbents for removal of some basic dyes, methylene blue and crystal violet, from aqueous solution. It was found that the adsorption capacity of the synthesised adsorbents depends on the preparation conditions such as NaOH:fly-ash ratio and fusion temperature with the optimal conditions being at 1.2:1 weight ratio of Na:fly-ash at 250-350 degrees C. The synthesised materials exhibit much higher adsorption capacity than fly ash itself and natural zeolite. The adsorption isotherm can be fitted by Langmuir and Freundlich models while the two-site Langmuir model producing the best results. It was also found that the fly ash derived geopolymeric adsorbents show higher adsorption capacity for crystal violet than methylene blue and the adsorption temperature influences the adsorption capacity. Kinetic studies show that the adsorption process follows the pseudo second-order kinetics.     

Remediation of copper ions from aqueous solution using hybrid magadiite: kinetics,isotherm and mechanism of removal

Research on Chemical Intermediates - This paper deals with the potential use of hybrid magadiite composite as an alternative adsorbent for the removal of copper ions. Na-magadiite was synthesized...     

Cation-independent electron transfer between ferricyanide and ferrocyanide ions in aqueous solution

Electron transfer between Fe(CN)(6)(3-) and Fe(CN)(6)(4-) in homogeneous aqueous solution with K(+) as the counterion normally proceeds almost exclusively by a K(+)-catalyzed pathway, but this can be suppressed, and the direct Fe(CN)(6)(3)(-)-Fe(CN)(6)(4-) electron transfer path exposed, by complexing the K(+) with crypt-2.2.2 or 18-crown-6. Fe((13)CN)(6)(4-)-NMR line broadening measurements using either crypt-2.2.2 or (with extrapolation to zero uncomplexed [K(+)]) 18-crown-6 gave consistent values for the rate constant and activation volume (k(0) = (2.4 +/- 0.1) x 10(2) L mol(-1) s(-1) and Delta V(0) = -11.3 +/- 0.3 cm(3) mol(-1), respectively, at 25 degrees C and ionic strength I = 0.2 mol L(-1)) for the uncatalyzed electron transfer path. These values conform well to predictions based on Marcus theory. When [K(+)] was controlled with 18-crown-6, the observed rate constant k(ex) was a linear function of uncomplexed [K(+)], giving k(K) = (4.3 +/- 0.1) x 10(4) L(2) mol(-2) s(-1) at 25 degrees C and I = 0.26 mol L(-1) for the K(+)-catalyzed pathway. When no complexing agent was present, k(ex) was roughly proportional to [K(+)](total), but the corresponding rate constant k(K)' (=k(ex)/[K(+)](total)) was about 60% larger than k(K), evidently because ion pairing by hydrated K(+) lowered the anion-anion repulsions. Ionic strength as such had only a small effect on k(0), k(K), and k(K)'. The rate constants commonly cited in the literature for the Fe(CN)(6)(3-/4-) self-exchange reaction are in fact k(K)'[K(+)](total) values for typical experimental [K(+)](total) levels.     

Removal and recovery of uranium from aqueous solution by tea waste

Experiments on the removal and recovery of U(VI) from aqueous solution by tea waste were conducted. The adsorbent was characterized by scanning electron microscope and energy dispersive spectrometer before and after the adsorption treatment. The removal of U(VI) amounts to 86.80?% at optimum pH 6. The adsorption process reaches its equilibrium in 12?h at 308?K, and the kinetic characteristic can be described by the pseudo-second-order kinetic equation. The amount of adsorption increases from 22.92 to 142.21?mg?g^?1 with the decrease of tea waste dosage from 100 to 10?mg for solution with an initial uranium concentration of 50?mg?L^?1. Desorption for the four strippants is higher than 80?%. The equilibrium data are more agreeable with Freundlich isotherm than Langmuir isotherm.     

Precipitation of uranium from nitrate-sulfuric eluates by aqueous ammonia solution

The process of uranium precipitation from nitrate-sulfuric acid eluates by a 25% aqueous solution of ammonia was investigated. The effect of precipitation pH value on the impurity composition, particle size and bulk density of the yellow cake was studied. It was found, that precipitation should be carried out at pH 6.7 to obtain a high-purity concentrate. The method makes it possible to obtain a concentrate with an uranium content of 71.79%, a high bulk density of 970 kg m^?3, an average particle diameter of 10.3 μm. The impurity composition of concentrate obtained at pH 6.7 meets the requirements of ASTM C967-13.