Aleksandra Rosić

THE INFLUENCE OF ACID TREATMENT ON THE COMPOSITION OF BENTONITE

Bentonite from the ‘Bogovina’ coal mine in Serbia, was characterized. The influence of acid treatment on its composition, as well as mathematical descriptions of this influence are reported. The purpose of this work was to correlate the concentration of the acid used for the treatment with the resulting bentonite composition. X-ray diffraction (XRD), infrared spectroscopy and quantitative chemical analysis were employed to define the changes caused by acid treatment.The contents of all the cations, except Si, decreased exponentially with increasing concentration of the HCl used for the treatment of the bentonite. This approach was tested on previously published data and was shown to be valid.The basal reflections of smectite decreased gradually and eventually disappeared after intense treatment, while the other reflections remained in the XRD patterns of all the samples, but decreased slightly with increasing acid strength. In addition, the amount of X-ray amorphous matter formed increased rapidly with increasing acid concentration up to 4.5 M. With further increase in the acid strength, the amount of X-ray amorphous matter remained virtually constant.

Mechanical activation of cement with addition of fly ash

Influence of mechanical activation on quality of cement with addition of fly ash was investigated. The experiments of mechanical activation were performed in laboratorial vibro mill with rings. The effects of mechanical activation were determined by the comparative analyses of the starting cement and the same cement treated mechanically for 3, 10 and 30 min. The analyses included determination of the specific surface area, X-ray diffractometric analysis (XRD), differential-thermal analysis (DTA) and thermogravimetric analysis (TGA). During the 30-min comminution period, the specific surface area was increasing, while the microstructural changes of portland cement with fly ash addition (20% wt.) were intensified. DT and TG analyses show that endothermic and exothermic reactions proceed at the lower temperatures, which is an indication of increased reactivity of mechanically activated sample. Physico-mechanical properties significantly improved after only 3 min activation. After the 3-min activation, i.e., the seven-day solidification, the increase in the compression strength is very well-expressed. However, even after the 28-day solidification, the compression strength of mechanically activated sample was 58% higher, in comparison with inactivated sample of the same composition. Also, after the 28-day solidification, the compression strength of portland cement with addition of fly ash, mechanically activated for 3 min, was approximately the same to the compression strength of portland cement without additives.

Toluene Degradation in Water Using AlFe-Pillared Clay Catalysts

Abstract The catalytic wet peroxide oxidation (CWPO) of toluene on two bentonite-based AlFe-pillared clays (PILCs) with different iron contents was investigated. The PILCs were obtained using bentonite clay from Bogovina, Serbia. The change in chemical and phase composition and textural properties of the starting clay and synthesized catalysts was monitored using X-ray diffraction, inductively coupled plasma optical emission spectrometry, UV-Vis diffuse reflectance spectrometry, and physisorption of nitrogen. The catalytic performance was examined using gas chromatography. The Na-exchange process lowered the (001) smectite basal plane spacing, but the clay retained its swelling properties, while the pillaring process increased it. The surface areas of both synthesized pillared clays increased to values although their Fecontent was different. At 37 °C, both catalysts show significant toluene degradation, with the one richer in Fe having higher efficiency. The leaching of the active cations during reaction was negligible, and the catalysts were stable. AlFe-pillared clay catalysts can be used in CWPO for the elimination of BTEX compounds from plant effluent streams.

Diffuse reflectance spectra of methylene blue adsorbed on different types of clay samples

Abstract Diffuse reflectance (DR) spectra in the visible (VIS) and near-infrared (NIR) region of methylene blue (MB) adsorbed on clay samples of different mineral composition and varying MB/clay ratios were analyzed. This type of investigation is not affected by unadsorbed MB molecules and can be used in clay-mineral determination. When the MB dye/clay loading was increased, enhancement of bands in the DR-VIS and DR-NIR was observed. The distribution of various MB aggregates was interpreted according to mineral composition and MB loading. The NIR spectrum of H2O overtone provides insights about the intercalated MB aggregation, consistent with VIS spectra. Critical MB concentration for formation of dimeric structure was between 0.7 and 1.75 mmol/100 g followed with suppression of monomers. Different orientations of vectors of polarized light allowed calculations of the possible orientation and tilting angle of MB molecules on the surface of the clay particles in accordance with XRD data.

Mineralogy and characterization of deposited particles of the aero sediments collected in the vicinity of power plants and the open pit coal mine: Kolubara (Serbia)

In this paper, particular attention was paid to the presence of aerosol solid particles, which occurred mainly as a result of exploitation and coal combustion in the thermal power plants of the Kolubara basin. Not all of the particles created by this type of anthropogenic pollution have an equal impact on human health, but it largely depends on their size and shape. The mineralogical composition and particle size distribution in the samples of aero sediments were defined. The samples were collected close to the power plant and open pit coal mine, in the winter and summer period during the year 2007. The sampling was performed by using precipitators placed in eight locations within the territory of the Lazarevac municipality. In order to characterize the sedimentary particles, several methods were applied: microscopy, SEM-EDX and X-ray powder diffraction. The concentration of aero sediments was also determined during the test period. Variety in the mineralogical composition and particle size depends on the position of the measuring sites, geology of the locations, the annual period of collecting as well as possible interactions. By applying the mentioned methods, the presence of inhalational and respiratory particles variously distributed in the winter and in the summer period was established. The most common minerals are quartz and feldspar. The presence of gypsum, clay minerals, calcite and dolomite as secondary minerals was determined, as well as the participation of organic and inorganic amorphic matter. The presence of quartz as a toxic mineral has a particular impact on human health.

Refractive indices of unfilled resin mixtures and cured composites related to color and translucency of conventional and low-shrinkage composites

This study correlated the refractive indices (RIs) of unfilled resin mixtures and resin-based composites (RBCs) with color and translucency of conventional and low-shrinkage RBCs. Unfilled resin mixtures based on different ratios of conventional monomers Bisphenol A-glycidyl-methacrylate (BisGMA)/triethyleneglycol-dimethacrylate (TEGDMA) and urethane-dimethacrylate (UDMA)/TEGDMA and a low-shrinkage monomer FIT-852 (FIT, Esstech Inc.)/TEGDMA were used to prepare model RBCs, containing 30 wt % of the organic matrix and 70 wt % of silanated barium-glass fillers (n = 1.553, Esstech Inc.). The RIs of resins were measured on an ABBE refractometer, those of cured RBCs using the Becke-line method in immersion oils. Color and translucency were determined using an AvaSpec-2048 (Avantes BV) spectrometer. The RIs of unfilled resin mixtures decreased with increasing amounts of TEGDMA. Cured RBCs had higher RIs than their respective resin mixtures. BisGMA-based composites were more translucent with significantly lower L* values than FIT- and UDMA-based RBCs. The RIs of unfilled resins positively correlated with cured RBCs (p = 0.001), as did the RIs with translucency (p = 0.001) and color (p = 0.008). Resin mixtures and corresponding RBCs based on UDMA and its modified low-shrinkage version, FIT, showed similar optical properties. The RIs of unfilled resins appeared to be good predictors of the RIs of cured RBCs.

Structural and textural properties of Al,Fe-pillared clay catalysts

Metal oxide pillared interlayered clays (PILCs) represent a new class of materials that have found a wide range of potential applications including catalytic oxidative degradation of organic pollutants in water. Al,Fe-pillared smectite clays with different Fe content were synthesized for possible catalytic application. Starting clay and the obtained PILCs were characterized. Phase composition, textural and morphological properties of the starting clay and synthesized PILCs were determined using X-ray diffraction, physisorption of nitrogen and scanning electron microscopy. Chemical composition of the PILCs was determined using EDX. It was found that the synthesized PILCs have similar phasal composition, textural and morphological properties differing only in Fe content in accordance with the amount of Fe introduced to clay during the pillaring process.