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Abstract  

Applicability of montmorillonite, manganese oxide-coated montmorillonite (MOCM) and iron oxide-coated montmorillonite (IOCM) as backfill materials in permeable reactive barrier (PRB) to remediate contaminated groundwater was investigated. Single- and bi-solute competitive sorptions of Co, Sr and Cs were conducted. The Freundlich, Langmuir and Dubinin-Radushkevich models fitted the single-solute sorption data well (R 2 > 0.95). Maximum sorption capacities (q mL) of Co and Sr predicted by the Langmuir model were in the order of MOCM (0.37 mmol/g for Co and 0.28 mmol/g for Sr) > montmorillonite (0.27 mmol/g for Co and 0.19 mmol/g for Sr) ≈ IOCM (0.23 mmol/g for Co and 0.21 mmol/g for Sr), while those of Cs were in the order of montmorillonite (1.11 mmol/g) > MOCM (0.68 mmol/g) > IOCM (0.62 mmol/g). In the bi-solute sorptions, the sorbed amount of one solute decreased due to the presence of the other competing metal ion. Langmuir model parameters for single-solute (q mL and b L) and bi-solute (

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$q_{\text{mL}}^{*}$$ \end{document}
and
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$b_{\text{L}}^{ *}$$ \end{document}
) sorptions were compared to analyze the effect of competition between the metal ions. The competitive Langmuir (R 2 > 0.81) and P-factor (R 2 > 0.82) models predicted the bi-solute competitive sorption data well but not the SRS model (0.003 < R 2 < 0.97).

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Abstract  

The sorption of radionuclide 63Ni(II) on bentonite/iron oxide magnetic composites was investigated by batch technique under ambient conditions. The effect of contact time, solid content, pH, coexistent electrolyte ions, fulvic acid, and temperature on Ni(II) sorption to bentonite/iron oxide magnetic composites was examined. The results demonstrated that the sorption of Ni(II) was strongly dependent on pH and ionic strength at pH <8.0, and was independent of pH and ionic strength at high pH values. The sorption of Ni(II) was dominated by outer-sphere surface complexation or ion exchange at low pH, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The experimental data were well fitted by Langmuir model. The thermodynamic parameters (∆G°, ∆S°, ∆H°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Ni(II) on bentonite/iron oxide magnetic composites was an endothermic and spontaneous processes. The results show that bentonite/iron oxide magnetic composites are promising magnetic materials for the preconcentration and separation of radionickel from aqueous solutions in environmental pollution.

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Abstract  

An irradiation position in the 250 kW Triga reactor was characterized for instrumental neutron activation analysis of chlorine in an iron oxide matrix. Factors that affect the accuracy of the determination include variations in the reactor neutron spectrum and flux as a function of spatial position and the presence of chlorine impurities. Gold wire and foils were used to determine the neutron flux and cadmium ratio as a function of height in an air-filled irradiation tube.

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Abstract  

In this paper we present a study regarding the obtaining of iron oxides embedded in silica matrix, using a modified sol-gel method. This method consists in the formation, inside the silica matrix, of some Fe(III)-carboxylate compounds, resulted in the redox reaction between Fe(NO3)3 and diol. We have synthesized four gels, starting from tetra-ethyl orthosilicate, Fe(NO3)3·9H2O and different diols: ethylene glycol, 1,2-propanediol, 1,3-propanediol and 1,4-butanediol, for a final composition 50% Fe2O3/50% SiO2. The obtained gels have been thermally treated at 130°C, when the redox reaction Fe(NO3)3-diol took place with formation of the precursors in the xerogels pores. The thermal decomposition of all four precursors took place up to 300°C. The samples obtained by annealing at 300, 500, 700°C of the four xerogels lead to crystalline phases inside the amorphous silica matrix. γ-Fe2O3/SiO2 may be obtained as unique phase depending on the diols nature. The formation of the precursors inside the silica matrix and the evolution of the crystalline phases were analyzed by thermal analysis, FTIR spectrometry and XRD.

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The thermal treatment of Fe2O3·1.65H2O gives rise to sharp dehydration weight-change waves (310–470 K and 470–670 K) which correspond to the loss of loosely-bound and stronglybound water, respectively. Analysis of the thermal waves was performed by the method of Šatava and Škvara (1969), the modified method of Coats and Redfern (1964) and the method of Blazejowski et al. (1983), and by applying a least squares straight line fit to the data. The A2 andA 3 decomposition mechanisms predominate in the first dehydration step, whereas anF 1 mechanism seems the best to describe dehydration of the structural water. Activation energies of 21 kJ · mol−1 and 95 kJ·mol−1 are estimated for the first and second steps, respectively.

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Abstract  

Samples of the composition of 10Fe2O3·10CaO·80SiO2 were prepared by the sol-gel method and heat-treated in different atmospheres. They were investigated by X-ray diffraction, scanning electron microscopy and Mössbauer spectroscopy. In the heat-treated samples in air iron is present up to 1000 °C in form of hematite and as Fe3+ in the tetrahedral sites. A wide range of hematite particle sizes was observed, the average size increased with heating temperature. At 1000 °C wollastonite was observed, at 1200 °C tridymite was formed and all the iron was incorporated in hematite. A heat-treatment at 500 °C under reducing conditions led to poorly crystallized maghemite and at 700 °C to metallic iron and fayalite formation.

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Abstract  

The adsorption of Zn2+ ions on amorphous Fe(OH)3 and -Fe2O3, as a function of pH, has been investigated. In the pH region corresponding to the formation of positively charged Zn-hydroxy complexes, an abrupt increase in adsorption was observed. The influence of EDTA and glycine on the adsorption of Zn2+ by -Fe2O3 has also been investigated. Strong suppression of the adsorption of Zn2+ was observed for high [EDTA or Gly]/[Zn2+] concentration ratios. The results of the adsorption of Zn2+ in the presence of an organic ligand were explained by the formation of Zn-EDTA or Zn-glycine complexes and also by the occupation of adsorption sites by the free organic ligand.

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Abstract  

The influence of the coordination architecture (materialized by ligand binding mode and content) on the thermal behaviour of coordination compounds containing copper, iron and oxalic anion as ligand was investigated. It was established that the metal-metal connections influence stronger, comparative with ligand content, the stoichiometry of the thermal decompositions.

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Abstract  

The paper presents results of research on the effect of the presence of calcium and magnesium in magnetite structure on its reducibility. These are model studies of the phase which mostly affects reducibility of superfluxed sinter. Examinations were carried out on samples melted and crystallized in a single crystal growing process.

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