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.     

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.     

Sorption of uranium(VI) from aqueous solution onto magnesium silicate hollow spheres

The sorption of uranium(VI) from aqueous solutions was investigated using synthesized magnesium silicate hollow spheres as a novel adsorbent. Batch experiments were conducted to study the effects of initial pH, amount of adsorbent, contact time and initial U(VI) concentrations on uranium sorption efficiency. The desorbing of U(VI) and the effect of coexisting ions were also investigated. Kinetic studies showed that the sorption followed a pseudo-second-order kinetic model. The Langmuir sorption isotherm model correlates well with the uranium sorption equilibrium data for the concentration range of 25–400 mg/L. The maximum uranium sorption capacity onto magnesium silicate hollow spheres was estimated to be about 107 mg/g under the experimental conditions. Desorption of uranium was achieved using inorganic acid as the desorbing agent. The practical utility of magnesium silicate hollow spheres for U(VI) uptake was investigated with high salt concentration of intercrystalline brine. This work suggests that magnesium silicate hollow spheres can be used as a highly efficient adsorbent for removal of uranium from aqueous solutions.     

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.     

Investigation of HEU-type zeolite crystals after interaction with Sr2+ cations in aqueous solution using nuclear and surface analytical techniques

Pure HEU-type zeolite (heulandite) crystals were allowed to interact with Sr²⁺ cations in aqueous solution. The powdered solid experimental products obtained from batch-type sorption experiments, using solutions of Sr²⁺-concentrations between 10 and 1000 mg/l, were investigated using INAA, RI-XRF and SEM-EDS. The Sr uptake by the mineral which can adequately be described with a Freundlich-type isotherm, varies from 3.14 to 6.22 mg/g. The distribution coefficients increase progressively by decreasing the solutions concentration reaching a value of 1800 ml/g. The investigated zeolite interacts with Sr²⁺ cations through ion exchange reactions and initial exchangeable Ca²⁺ cations are replaced into the structural micropores. However, in the best case, only ca. 43% of the theoretical CEC can be covered because of the limited availability of the extra framework Ca²⁺ cations that can be removed from the lattice under ambient treatment conditions. The XPS investigation of Sr-loaded single crystals indicated that adsorption of Sr²⁺ cations on the outer surface also occurs while surface precipitation phenomena must be excluded. Similar surface analyses by means of¹²C-RBS showed that the Sr depth-distribution at near-surface layers is quite homogenous in contrast to a previous relevant study revealing an intense surface Sr-accumulation on a natural Ca-zeolite of different structural characteristics (scolecite).     

Kinetics of Sorption,Desorption, and Diffusion in Zeolites

Sorption and desorption in zeolites (molecular sieves) have to be considered as complex processes, involving simultaneous diffusion in zeolite crystals, mass transfer in the intercrystalline void of a pellet, and heat transfer between the zeolitic sorbent and its surroundings. The kinetics of sorption and desorption, respectively, of n-C₄H₁₀ in zeolite X and of CO₂ in zeolite A have been investigated: only the initial rates of uptake or release of the sorbet are controlled by mass transfer alone whereas ultimately they also depend on the rate of heat transfer from the sorbent to its surroundings or vice versa. Diffusivities of the sorbate in the zeolite crystals can be obtained from the kinetics of mass transfer, provided the resistance due to viscous or Knudsen flow between the crystals of the zeolitic sorbent can be eliminated. A sample consisting of a monolayer of single crystals had to be used for this purpose in the n-butane/zeolite X system; the intracrystalline diffusivity obtained in this way is not in conflict with data obtained by NMR spectroscopy. The intracrystalline diffusivities obtained in this way—taking into account the coupling of several processes during sorption — are higher than values reported in the literature.     

Uranium removal from acidic aqueous solutions by <Emphasis Type="Italic">Saccharomyces cerevisiae,Debaryomyces hansenii,Kluyveromyces marxianus</Emphasis> and <Emphasis Type="Italic">Candida colliculosa</Emphasis>

The sorption of uranium from acidic aqueous solutions (pH 4.5, C _init = 10 to 1000 mg U/L) by Saccharomyces cerevisiae, Debaryomyces hansenii, Kluyveromyces marxianus and Candida colliculosa was investigated using a batch technique. The U-sorption onto Saccharomyces cerevisiae and Debaryomyces hansenii followed a Langmuir, while that onto Kluyveromyces marxianus and Candida colliculosa a Freundlich isotherm. The results demonstrated that all investigated biomasses could effectively remove uranium from acidic aqueous solutions. From all sorbents, Saccharomyces cerevisiae appeared to be the most effective with a maximum sorption capacity of 127.7 mg U/g dry biomass.     

Sorption characteristics of uranium onto composite ion exchangers

The composite ion exchangers were tested for their ability to remove UO₂ ²⁺ from aqueous solutions. Polyacrylonitrile (PAN) composites having natural zeolite, clinoptilolite, and synthetic zeolite, zeolite X, were used as an adsorbents. The influences of pH, U(VI) concentration, temperature and contact time on the sorption behavior of U(VI) were investigated in order to gain a macroscopic understanding of the sorption mechanism. The optimum adsorption conditions were determined for two composites. The sorption behaviors of uranium on both composites from aqueous systems have been studied by batch technique. Parameters on desorption were also investigated to recover the adsorbed uranium.     

Colloidal Regularities of the Interaction between Uranium(VI) and the Cells of Metal-Resistant Bacillus cereus AUMC 4368 Bacterial Culture

Sorption of uranium(VI) by the cells of metal-resistant Bacillus cereus AUMC 4368 bacterium was studied in aqueous solutions as a function of pH, equilibrium concentration of metal, and the presence of co-ions with account of the changes in phase state of metals and biocolloids. Experimental data indicate that the sorption of uranium(VI) by negatively charged biocolloids is maximal at pH 4.2–4.5 (1.2 mM per 1g of dry biomass), when metal is present in the form of positively charged hydroxocomplexes. At pH 8, the interaction between uranium(VI) and the cells is inhibited due to the formation of negatively charged water-soluble hydroxocarbonate complexes and uranate ions. Co, Sr, Cu, Ca, Mg, and Zn ions do not influence the efficiency of sorption of uranium(VI) in a weakly acidic medium, but can cause inhibiting effect in neutral pH region. The most pronounced effect expressed in broadening of sorption range and in the heterocoagulation of uranyl is observed in the presence of Fe³⁺ ions. It was established that the binding of uranium(VI) occurs by the carboxyl surface groups of Bacillus cereuscell surface. Uranium(VI) is irreversibly bound by the carboxyl groups of cell surface and its efficient desorption is possible only during the interaction with citric acid or sodium hydrocarbonate with the formation of water-soluble complexes transferred to aqueous phase. It was shown that uranyl in the form of organocomplexes (citric, humatic, and fulvatic) is not sorbed by biocolloids.     

Removal of uranium anionic species from aqueous solutions by polyethylenimine–epichlorohydrin resins

The removal of uranium anionic species from aqueous solutions (initial concentration: 10–2,000 mg/L) by a low- and a high molecular weight polyethylenimine–epichlorohydrin resins was studied in the absence of background electrolytes at initial pH (pH_init) 8 to10. The amount of the sorbed U was determined spectrophotometrically using the Arsenazo III method. The maximum uptake was observed at pH_init 8 using both resins. The maximum uptake capacity observed was 221 and 388 mg U/g for the low- and high molecular weight resin respectively. The uptake data were modeled using a number of 2- and 3- parametric isotherm equations (Langmuir, Freundlich, Langmuir–Freundlich, Toth and Redlich–Peterson). The kinetics of the uranium removal was also studied and modeled using the pseudo-first and pseudo-second order equations. The surface and interior of the resin grains were examined after the sorption experiments by scanning electron microscopy/energy dispersive spectroscopy.     

Sorption of neptunium on clays

Batch sorption experiments with²³⁷Np using kaolinite and molasse clays were carried out under oxic conditions. The sorption kinetics and the effects of particle size of clay samples, concentration of neptunium in the solutions and the pH below and above the point of zero charge of the clays on the sorption coefficients were studied. The sorption coefficients of neptunium, on kaolinite were between 23 and 1100 ml/g at pH 1.5 and 7.6, respectively, whereas, sorption on the molasse clay was not affected significantly by pH (R_d600 ml/g).     

The Equilibrium and Kinetic Modelling of the Biosorption of Copper(II) Ions on <Emphasis Type="Italic">Cladophora crispata</Emphasis>

The biosorption of Cu(II) ions on Cladophora crispata was investigated as a function of the initial pH, temperature and initial Cu(II) ion concentration. Algal biomass exhibited the highest Cu(II) uptake capacity at 25C and at the initial pH of 4.5. Equilibrium data fitted very well to both the Langmuir and Freundlich isotherm models. The pseudo second order kinetic model was applied to describe the kinetic data and the rate constants were evaluated in the studied concentration range of Cu(II) ions at all the temperatures studied. The experimental data fitted well to the pseudo second order kinetic model with a high correlation coefficient (R² > 0.99), which indicates that the external mass transfer limitations in the system can be neglected and the chemical sorption is the rate-limiting step. The pseudo second order kinetic constants were also used to calculate the activation energy of Cu(II) biosorption.     

Interaction of granitic biotite with selected lanthanides and actinides

The interaction of granitic biotite with aqueous solutions of La, Nd, Th and U (concentration 10 to 1000 mg·l^-1) was studied using instrumental neutron activation analysis (INAA) and ¹²C-Rutherford backscattering spectroscopy (¹²C-RBS). For comparison, the sorption of La and Nd by granitic feldspar and natural zeolite heulandite was also investigated. The experimental results showed that biotite exhibits higher sorption ability towards La and Nd, (maximum uptake 2.09 and 7.98 mg/g, respectively) than the feldspar and the heulandite. The interaction of biotite with Th is also intense, the metal being preferably concentrated at the near-surface layers of the crystals. This indicates that other sorption mechanisms (adsorption and surface precipitation) than ion-exchange take place at the solid/solution interface. The same phenomenon was also observed in the case of U, although the corresponding metal uptake was found to be considerably lower.     

Ethylenediamine effect on Co2+ uptake by zeolite Y

Co²⁺ ion exchange, at room temperature, from aqueous cobalt — sodium chloride solutions with NaY zeolite has been studied. The effect of contact time on the shape of the sorption curves of Co²⁺ using zeolite Y dehydrated at 600°C is similar to the one found in our previous work with a zeolite dehydrated at 150 °C. A fast sorption uptake is observed in which 1.8 meq of Na⁺ ions/g of zeolite are replaced by cobalt ions followed by a desorption process where the uptake decreases to 1.2 meq/g zeolite. The Co²⁺ sorption using zeolite Y dehydrated at 600 °C is increased when ethylenediamine solution is passed through the zeolite. The Co²⁺ sorption uptake, initially 2.0 meq/g, incrases to 2.8 meq/g of zeolite. This behavior is explained by the location and coordination of cobalt in zeolite Y sites. It is suggested that the highest uptake process is due to the blocking of zeolite sites by a Co complex compound.     

Removal of thorium from aqueous solutions by sodium clinoptilolite

Adsorptive behavior of natural clinoptilolite was assessed for removal of thorium from aqueous solutions. Natural zeolite was characterized by X-ray diffraction and X-ray fluorescence. The zeolite sample composed mainly of clinoptilolite. Na-exchanged form of zeolite was prepared and its sorption capacity for removal of thorium from aqueous solutions was examined. The effects of relevant parameters, including initial concentration, contact time, solid to liquid ratio, temperature and initial pH on the removal efficiency were investigated in batch studies. The pH strongly influenced thorium adsorption capacity and maximal capacity was obtained at pH 4.0. Kinetics and isotherm of adsorption were also studied. The pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion models were used to describe the kinetic data. The pseudo-second-order kinetic model provided excellent kinetic data fitting (R ² > 0.999) with rate constant of 1.25, 1.37 and 1.44 g mmol⁻¹ min⁻¹ respectively for 25, 40 and 55 °C. The Langmuir and Freundlich models were applied to describe the equilibrium isotherms for thorium uptake and the Langmuir model agrees very well with experimental data. Thermodynamic parameters were determined and are discussed.     

Complex Sorption Kinetics of Carbon Dioxide in NaX-Zeolite Crystals

Ad-/desorption-kinetic measurements were performed for carbon dioxide on a mono-disperse crystal sample of NaX-type zeolite (mean crystal diameter: 2R (100 ± 6) m) by a constant-volume–variable-pressure method in a differential concentration mode over ranges of temperature, (193–293) K, and pressure, (20–26,700) Pa. They revealed a complex sorption process in sorbate uptake and release during experiments of ad- and desorption, respectively, which is comprised of a slow, hitherto unknown rate mechanism superimposed on very fast intracrystalline diffusion of carbon dioxide. IR-spectroscopic data that evidence formation of chemisorption species in CO₂-NaX sorption systems may allow for a tentative interpretation of this finding. Circumstantial evidence for the correctness of this conclusion follows from sorption–kinetic experiments for carbon dioxide on BaKX-type zeolite crystals (mean crystal diameter: 2R (120 ± 6) m).     

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.     

The effect of surfactants and complexing agents on the fluorimetric determination of uranium

Summary The effect of surfactants, condensed phosphates, soap, EDTA, NTA, citric acid, oil and Alamine-336 on the fluorimetric determination of uranium in a 5-ml aqueous sample extracted with methyl isobutyl ketone after addition of saturated calcium nitrate or 1N acid-deficient saturated aluminium nitrate salting-out solutions has been established. The error produced by these compounds, even at concentrations up to 500 mg/l, does not exceed ±10%, except for anionic LAS-type detergent, which at above the 50 mg/l level forms stable emulsions after extraction from solutions containing the acid-deficient aluminium nitrate salting-out reagent. Up to 1 hour of standing time after extraction may be required for the emulsions to break. The detection limit for uranium is 1.1g/l (2s).

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Zusammenfassung Die Wirkung von Schaummitteln, Polyphosphaten, Seifen, ÄDTA, NTA, Zitronensäure, Öl und Alamin-336 bei der fluorimetrischen Uranbestimmung in einer wäßrigen 5-ml-Probe nach Extraktion mit Methylisobutylketon aus einer mit gesättigtem Calciumnitrat oder säurefreier gesättigter Aluminiumnitratlösung zwecks Aussalzung versetzten Lösung wurde beschrieben. Der durch diese Verbindungen verursachte Fehler übersteigt auch bei Konzentrationen bis zu 500 mg/l nicht ±10%, mit Ausnahme anionischer Detergentien vom LAS-Typ (lineare Alkylsulfonate), die oberhalb 50 mg/l nach Extraktion aus Lösungen, die säurefreies, gesättigtes Aluminiumnitrat enthalten, stabile Emulsionen bilden. Um diese zu beseitigen, muß man nach der Extraktion 1 Stunde stehen lassen. Die Nachweisgrenze für Uran beträgt 1,1gmg/l (2s).

     

Aufnahme von Spurenmengen Antimon (Radioantimon) durch einige Metalloxidhydrat-Niederschläge

Zusammenfassung Mit trägerfreiem¹²⁵Sb bzw. trägerarmem¹²⁴Sb wurde die Aufnahme von Spurenmengen Antimon(III) durch Fe(III)-, Al-, Zr- und Ti-Oxidhydrat untersucht. Für die Aufnahme von Antimon durch Mitfällung wurde gefunden: ZrTi>Fe Al. Bei Mitfällung aus 1M-NaCl und bei pH 7 sind etwa folgende Metallionenmengen erforderlich, um Antimon zur Hälfte mitzufällen: Zr oder Ti 0,02 mMol/l, Fe 0,1 mMol/l bzw. Al 3 mMol/l. Bei Fe-, Zr- und Ti-Oxidhydrat beträgt die Radioantimonaufnahme durch Mitfällung das 5- bis 8fache der Aufnahme durch Sorption an vorgebildeten Niederschlägen. Bei Mitfällung überwiegt daher hier Einbau in das Innere des Niederschlags sehr stark gegenüber Adsorption an der Oberfläche. Versuche mit Radiostrontium (trägerarmem⁸⁵Sr) ergeben im Gegensatz hierzu, daß bei Fe-, Al- und Ti-Oxidhydrat Mitfällung und Sorption an vorgebildeten Niederschlägen zu ungefähr gleich starker Aufnahme führen. Ferner wurde die Abhängigkeit der Radioantimonaufnahme vom pH und von der NaCl-Konzentration der Lösungen ermittelt und daraus Schlüsse auf die Natur des Aufnahmeprozesses gezogen.

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Uptake of trace amounts of antimony (radioantimony) by precipitates of some hydrated metal oxides

Uptake of trace amounts of antimony(III) by the hydrated oxides of Fe(III), Al, Zr and Ti was investigated using carrier-free¹²⁵Sb or¹²⁴Sb of high specific activity. For uptake of antimony by coprecipitation, the following order was found: ZrTi>FeAl. The amounts of metal ions required to coprecipitate half of the antimony from 1M-NaCl at pH 7 are: Zr or Ti-0.02 mMol/l, Fe-0.1 mMol/l, Al-3 mMol/l. With the hydrated oxides of Fe, Zr and Ti, uptake of radioantimony by coprecipitation is 5 to 8 times as great as uptake by sorption on preformed precipitates. In coprecipitation, incorporation into the interior of these precipitates thus exceeds adsorption on the surfaces considerably. In contrast, experiments with radiostrontium (⁸⁵Sr of high specific activity) have shown that for the hydrated oxides of Fe, Al and Ti uptake by sorption on preformed precipitates is about equal to that by coprecipitation. Dependance of uptake of radioantimony upon pH and concentration of NaCl was also determined and conclusions regarding the nature of the processes responsible for uptake were drawn.

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Mit 7 Abbildungen

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FürE. B. (Univ.-Prof. Dr.Engelbert Broda) mit herzlichen Wünschen zum 60. Geburtstag.     

Adsorption of uranium from aqueous solution using HDTMA+-pillared bentonite: isotherm, kinetic and thermodynamic aspects

The ability of hexadecyltrimethylammonium cation pillared bentonite (HDTMA⁺-bentonite) has been explored for the removal and recovery of uranium from aqueous solutions. The adsorbent was characterized using small-angle X-ray diffraction, high resolution transmission electron microscopy, and Fourier transform infrared spectroscopy. The influences of different experimental parameters such as solution pH, initial uranium concentration, contact time, dosage and temperature on adsorption were investigated. The HDTMA⁺-bentonite exhibited the highest uranium sorption capacity at initial pH of 6.0 and at 80?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° (308?K), ??H°, and ??S° were determined to be ?31.64, ?83.84?kJ/mol, and ?169.49?J/mol/K, respectively, which demonstrated the sorption process of HDTMA⁺-bentonite towards U(VI) was feasible, spontaneous, and exothermic in nature. The adsorption on HDTMA⁺-bentonite was more favor than Na-bentonite, in addition the saturated monolayer sorption capacity increased from 65.02 to 106.38?mg/g at 298?K after HDTMA⁺ pillaring. Complete removal (??100%) of U(VI) from 1.0?L simulated nuclear industry wastewater containing 10.0?mg U(VI) ions was possible with 1.5?g HDTMA⁺-bentonite.