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Abstract  

Incorporation of iron oxide into silico-antimonate of different Si/Sb molar ratios introduced a class of dual salts ion exchangers with advanced ion exchange properties. Physicochemical and equilibrium studies have been carried out to understand the ion exchange properties of these materials. Apparent investigation indicated that iron incorporation into silico-antimonate yields materials having excellent mechanical properties. On the basis of distribution studies, the materials were found to be highly selective for Sr2+ or Ce3+ depending on their Si/Sb molar ratios. Diffractogram, thermogram, IR spectra and sorption performance of crystalline FeSiSb (114) indicated that no detectable structural changes after an exposure up to 100 kGy of γ-rays. Effect of reaction temperature on the exchange process was investigated and the respective thermodynamic parameters were calculated.

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Abstract  

A method is described which can be used to investigate the interaction of dissolved metals with particulate material. Low level concentrations (10–9M) of rare earth radiotracers were used to investigate their sorption onto synthetic mineral oxide surfaces. The preparation of rare earth radiotracers by neutron activation is discussed in detail. A kinetic approach was employed to investigate the interaction of dissolved metals and suspended mineral oxides. Amorphous iron oxyhyroxide, a phase commonly found in nature, was used in sorption experiments carried out in seawater at pH 7.8 and 2°C. Results of this study indicate a high affinity of the rare earth elements (REE) for the iron oxide surface (evidenced by fast uptake and high partition coefficients) and reveal a fraction between light and heavy REE.

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Abstract  

Hydrated iron oxide or amorphous-Fe2O3·3.5 H2O (HFeO), hydrated titanium oxide (HTiO) and hydrated thorium oxide (HThO) were synthesized and their applicability for the decontamination of intermediate level liquid wastes (ILLW) was tested. The sorption of a few actinides like plutonium and americium on HFeO, 137Cs and 106Ru on HTiO and 90Sr on HThO was investigated as a function of pH, time and loading capacity of the hydrous oxide with metal ions. The influence of the total dissolved salt content was also monitored. Some of these parameters influenced the sorption behavior significantly. The radiation stability of these inorganic sorbents were studied by irradiating them up to 48 Mrad. Adsorbed actinides and fission products were successfully eluted from HFeO and from the mix-bed of HTiO and HThO by 0.5M nitric acid.

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Abstract  

Geological and geochemical events were elucidated in by using U series nuclides in combination with chemical leaching technique. Two examples were examined: (1) in the apatite-bearing sediment column samples U(VI) is moving, while U(IV) in the samples is almost retained, and (2) the redistribution of U occurred along the column under the monsoon climate. On the other hand, U in the conglomerate sample is divided into 5 categories by the leaching technique, which are related with exchangeable, carbonate, iron oxide, organic/sulfide and silicate components, respectively. Uranium is shown to be abundant in the carbonate and iron rich fractions of conglomerate sediment. Appropriate models are proposed in each case study.

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Abstract  

During the past several years, a significant effort has been on investigation of reaction front propagation and the rate of energy release in heterogeneous systems consisting of nanopowder reactants. Substantial size reduction of each reactant powder (e.g. from micro- to nano-size) leads to increase of reaction front propagation in some systems under unconfined conditions by approximately two to three order of magnitude. This paper presents key challenges associated with processing and use of nanothermite materials and characterization of nanoreactants. Reaction constants, such as activation energies and frequency factors were determined using DSC technique for several nanothermite systems based on nanosize aluminum and iron oxide, bismuth trioxide, and molybdenum trioxide. Experimental data of ignition delay times for different nanothermite systems using laser energy source were compared well to those predicted by proposed mathematical model.

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Journal of Thermal Analysis and Calorimetry
Authors: P. Sánchez-Soto, A. Ruiz-Conde, R. Bono, M. Raigón, and E. Garzón

Abstract  

The thermal evolution of a slate rock sample (Berja, Almería, Spain) has been studied. The phase minerals identified in this sample were mica (illite), chlorite (clinochlore) and quartz as major components, with minor microcline, iron oxide and a mixed-layer or interstratified phase (montmorillonite-chlorite). This slate is highly silico-aluminous (48.33 mass% silica, 22.04 mass% alumina), and ca. 20 mass% of other elements, mainly Fe2O3 (8.35 mass%), alkaline-earths and alkaline oxides. Two main endothermic DTA effects, centered at 640 and 730°C, were observed. The more important contribution of total mass loss (7.15 mass%) was found between 500–900°C, with two DTG peaks detected at 630 and 725°C. All these effects were associated to the dehydroxylation of structural OH groups of 2:1 layered silicates mixed in the slate. The dehydroxylation of the layered silicates evidenced by dilatometry, produced a rapid increase of expansion between 600–800°C. The thermal evolution of the slate upper 800°C indicated the first sintering effects associated to shrinkage, which is also favoured by its low particle size (average 23 μm) and the presence of a liquid or vitreous phase as increasing the heating temperature. The application of thermal diffractometry to the slate sample allowed to study the formation of dehydroxylated crystalline phases from the layered silicates after heating. At 1000°C, β-quartz, dehydroxylated illite, iron oxide, relicts of microcline and the vitreous phase were present in the sample. All these results are interesting to know the thermal behaviour of a complex mineral mixture as identified in the slate.

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Abstract  

To demonstrate the safety performance assessment for the disposal of 134Cs radionuclide in a geological formation, several investigations were required to calculate the possible release of radionuclides into groundwater. This research examined the sorption behavior of radioactive cesium (134Cs) in natural groundwater. Cesium chloride (10-6 to 10-2 mol.l-1) was used as a carrier, traced with 134Cs radionuclide. Distribution coefficients of radiocesium for sorption and desorption were measured on natural soil samples of different grain size fractions (400 to 36 mm). Cesium sorption and desorption were found reversible at cesium chloride concentrations between 10-6 mol.l-1 to less than 10-3 mol.l-1. Sequential extraction procedures showed that the cesium sorption on soils were of various types: those easily desorbed, ion-exchanged, bound to carbonate, iron oxides, and organic matter. To demonstrate the safety performance assessment for the disposal of 134Cs radionuclide in a geological formation, several investigations were required to calculate the possible release of radionuclides into groundwater. This research examined the sorption behavior of radioactive cesium (134Cs) in natural groundwater. Cesium chloride (10-6 to 10-2 mol.l-1) was used as a carrier, traced with 134Cs radionuclide. Distribution coefficients of radiocesium for sorption and desorption were measured on natural soil samples of different grain size fractions (400 to 36 mm). Cesium sorption and desorption were found reversible at cesium chloride concentrations between 10-6 mol.l-1 to less than 10-3 mol.l-1. Sequential extraction procedures showed that the cesium sorption on soils were of various types: those easily desorbed, ion-exchanged, bound to carbonate, iron oxides, and organic matter.

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Abstract

The Ab Ask mineral springs are located 85 km northeast of Tehran, in the southern range of the Damavand volcano. Deposits of these calcareous springs are mainly precipitated as travertine. Petrographical, mineralogical, and stable isotope studies were conducted on different types of travertine to determine their genesis and factors that govern carbonate precipitation. Based on sedimentation consequence and lithofacies these travertines are categorized as first type (fresh travertine), second type (fissure-ridge, dam, and cascade), and third type (laminated) travertines, illustrating a specific condition of formation, deposition and diagenesis. Combined XRD and microscopic investigations show that the Ab Ask travertines are is composed of about 95 % calcite and a minor amount of quartz along with iron oxide impurities. The origin and transport of springs water from which travertine was precipitated are elucidated by 13C and 18O isotopic studies of the travertines. δ18O and δ13C values of travertines increase (from −13.0 to −6.3% VPDB and from 6 to 9.8% VPDB, respectively) with increasing distance from the spring orifice. This significant increase is attributed to temperature decrease, rapid degassing of CO2, and biological activities. It seems that CO2 content of these fluids may have originated from limestone decarbonation. Based on the integrated petrographic and stable isotope study, the Ab Ask travertines can could be thermogenic in origin.

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Members of the siderite-magnesite series of carbonates have been investigated in nitrogen using differential scanning calorimetry. The mineral specimens contained between 0.3–0.95 mole fraction iron. Decomposition temperatures decreased markedly with increasing Fe substitution. Enthalpies of decomposition showed a linear dependence upon the degree of Fe and Fe + Mn substitution. The fit (R 2=0.995) in the case of Fe + Mn suggested that DSC can be used to distinguish members of the series. Decomposition products consisted of substituted iron oxides in most cases.

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Abstract  

In soil science (ca. 1970), bromide ion (Br) in various forms (e.g., KBr, NaBr, SrBr2) was introduced as a non-reactive stable tracer in solute transport studies normally moving freely with the flux of water without substantial chemical or physical interactions with the soil. Typically, Br is extracted from soil and quantified using either a bromide selective electrode (sensitivity is ≈10μg/ml) or by high-performance liquid chromatography (sensitivity is ≈0.010 μg/ml). Where the sensitivity is adequate, the selective conductivity method, which is simple, affordable and fast, is preferred. More recently (ca. 1990), workers have reported that 20% of Br tracers, at low groundwater pH, may be adsorbed by iron oxides and kaolinite when present in the alluvial aquifer. We investigated the use of Epithermal Neutron Activation Analysis (ENAA) as a means of measuring Br directly in soil samples without an extraction. ENAA was chosen because of its high theoretical advantage factor over aluminum (i.e. ≈20), the principal interfering soil constituent, calculated for the79Br(n,γ)80Br reaction compared to27Al(n, γ)28Al. Br was measured (sensitivity is ≈0.050 μg/g) in one gram soil samples from a 5 s irradiation (φepi=2.5·1012 n·cm-2·s-1) using a BN capsule.

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