Adsorption equilibrium and kinetics of U(VI) on beta type of akaganeite

WOS: 000283474900031The use of cheap, high efficiency and low-risk adsorbent has been studied for the removal of U(VI) from aqueous solutions. A series of experiments was conducted in a batch system to assess the effect of the system variables, i.e. initial pH, temperature, initial uranium concentration and contact time. The results of these parameters were given in the previous work. In this paper Langmuir, Freundlich, Temkin, Dubinin-Radushkevich (D-R) and Harkins-Jura isotherms were used to analyze the equilibrium data at different temperatures. Adsorption process fitted to Langmuir and Temkin isotherm models. Also the adsorption kinetics was found to follow pseudo-second-order rate kinetic model, with a good correlation (R(2)>0.99) and intraparticle diffusion as one of the rate determining steps. The findings of this investigation suggest that the chemical sorption plays a role in controlling the sorption rate. (C) 2010 Elsevier B.V. All rights reserved

Chemical durability and structural analysis of PbO-B2O3 glasses and testing for simulated radioactive wastes

WOS: 000331495500023Lead borate based glass formulations with high chemical durability and lower melting temperatures compared to the currently used glasses were developed as candidates for the vitrification of radioactive waste. Properties including chemical durability, glass transformation temperature, and melting temperature were analyzed. The chemical durability of PbO-B2O3 glasses with PbO contents ranging from 30 to 80 mol% was determined. An average dissolution rate of 0.2 g m(-2) day(-1) was obtained for the composition 80PbO center dot 20B(2) O-3. These glasses were studied under simulation conditions and showed good potential as a vitrification matrix for radioactive waste management. Clear vitrified waste products containing up to 30 mol% SrO and 25 mol% Cs2O could be obtained. Leaching rates are about hundred times higher in low PbO glasses compared to high PbO glasses. These results are encouraging since they open up new horizons in the development of low melting temperature lead borate glass for waste immobilization applications. (C) 2013 Elsevier B.V. All rights reserved.Ege University, Scientific Research Projects CommissionEge University [09NBE003]This study was financially supported by the Ege University, Scientific Research Projects Commission (Project No: 09NBE003)

Magnesium oxide nanoparticles: Preparation, characterization, and uranium sorption properties

WOS: 000310261600006The objective of this work was to study the sorption of uranium (VI) ions on magnesium oxide (MgO) from aqueous solutions. The MgO has been prepared via hydroxide precipitation followed by thermal decomposition of the hydroxide. MgO was characterized by X-ray powder diffraction, scanning electron microscope, and multipoint Brunauer, Emmett, and Teller. The relative importance of test parameters such concentration of adsorbate, pH, contact time, and temperature on adsorption performance of MgO for U(VI) ion were studied and the optimum sorption efficiency was found as 87.61 +/- 3.10%. Desorption tests were also carried out and desorption efficiency was found as 100% with NH4Cl and NaNO3 solutions containing 0.1 M on a single step. Typical sorption isotherms (Freundlich and Dubinin-Raduskevich) were determined for the mechanism of sorption process and thermodynamic constants (?H degrees, ?S degrees, and ?G degrees) were calculated as -8.738 kJ mol-1, -21.68 kJ mol-1, and 0.102 kJ mol-1 K-1, respectively. (C) 2011 American Institute of Chemical Engineers Environ Prog, 2011Unit of the Scientific Research Projects of Ege UniversityEge UniversityThe authors are grateful for the financial support of the Unit of the Scientific Research Projects of Ege University

Adsorptive removal of thorium (IV) using calcined and flux calcined diatomite from Turkey: Evaluation of equilibrium, kinetic and thermodynamic data

WOS: 000312358100016Adsorption experiments were performed under batch process, using Th(IV) initial concentration, pH of solution, contact time and temperature as variables. Th(IV) uptake by calcined (C-D) and flux calcined diatomite (FC-D) was pH dependent (pH range, 3.0-6.0) and maximum sorption was observed at pH 4.0. Sorption capacities for Th(IV) were found to be 0.52 (121.22 mg Th/g) and 0.50 mmol/g (116.69 mg Th/g) for calcined diatomite (C-D) and flux calcined diatomite (FC-D), respectively. Adsorption process is well described by Freundlich and Dubinin-Radushkevich (D-R) isotherms in comparison with Langmuir, Temkin and Flory-Huggins isotherms. Thermodynamic data (Delta H degrees, Delta S degrees, Delta G degrees) were calculated from the temperature-dependent sorption isotherms. Results suggested that the adsorption of Th(IV) on calcined and flux calcined diatomite was a spontaneous and endothermic process. A comparison of kinetic models applied to the adsorption of Th(IV) onto C-D and FC-D was evaluated for the pseudo-first-order, pseudo-second-order, intraparticle diffusion and film diffusion kinetic models. The experimental data fitted very well the pseudosecond-order kinetic model and also followed by intra-particle diffusion model, whereas intraparticle diffusion and film diffusion are both the rate limiting steps for Th(IV) onto calcined and flux calcined diatomite. (C) 2012 Elsevier B.V. All rights reserved

Assessment of different hazard indices around coal-fired power plants in Turkey

This paper presents the radiological and heavy metal risk assessment to evaluate the impact of coal-fired power plants on humans and the environment in Turkey. Radiological evaluation was performed in terrestrial and freshwater ecosystems. For the freshwater reference organisms, total dose rates for insect larvae, mollusc bivalve, and gastropod, and zooplankton show radiological risk. Non-carcinogenic and carcinogenic risks, contamination factor, ecological risk, and geoaccumulation index for heavy metal risk assessment are the aspects of interest. Long-term exposure of children to heavy metals in coal may cause non-carcinogenic harmful effects

Kinetic modeling of selenium (IV) adsorption for remediation of contaminated aquatic systems based on meso-scale experiments

The present study involves selenium (IV) adsorption onto organic pillared bentonite using batch experiments and kinetic modeling, at two different temperatures. selenium (IV) remediation in an aqueous environment, such as contaminated drinking water, groundwater, and industrial wastewater, is the aim of this study. The experimental data were tested with both surface reaction-based and diffusion-based kinetic models to clarify the controlling mechanism of the adsorption process from both microscopic and macroscopic point of view. Among all the investigated models, the most appropriate was the pseudo-second-order surface reaction-based kinetics model. The obtained results proved that the adsorption process at a selenium dioxide concentration of 300mgL(-1) is controlled by the diffusion rate of penetrated selenium (IV) into the reacted layer

Sorption of Th(IV) onto ZnO nanoparticles and diatomite-supported ZnO nanocomposite: kinetics, mechanism and activation parameters

WOS: 000384108400003In this study, for the first time ZnO nanoparticles and diatomite-supported ZnO nanocomposite have been utilized as adsorbent for the removal of Th(IV) ions from aqueous solutions under different experimental conditions. The Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) isotherms were used to analyze the equilibrium data. The sorption equilibrium data were fitted well to the Langmuir isotherm with maximum sorption capacities values was found to be 1.105 mmol/g and 0.320mmol/gfor ZnO nanoparticles and diatomite-supported ZnO nanocomposite, respectively. Pseudo-first and pseudo-second order equations, Intraparticle diffusion and Bangham's models were considered to evaluate the rate parameters and sorption mechanism. Sorption kinetics were better reproduced by the pseudo-second order model (R-2 > 0.999), with an activation energy (E-a) of +99.74kJ/mol and +62.95kJ/mol for ZnO nanoparticles and diatomite-supported ZnOnanocomposite, respectively. In order to specify the type of sorption reaction, thermodynamic parameters were also determined. The evaluated Delta G* and Delta H* indicate the non-spontaneous and endothermic nature of the reactions. The results of this work suggest that both of the used materials are fast and effective adsorbents for removing Th(IV) from aqueous solutions and chemical sorption plays a role in controlling the sorption rate.Ege UniversityEge University [2012 NBE 015]This project was supported by Ege University Scientific Research Project Unit Project No. 2012 NBE 015. The research for this paper was carried out at the Institute of Nuclear Sciences, Ege University, Bornova-Izmir, within the frame of ERASMUS Program