From the aspect of their chemical and mineralogical composition, bauxites are very complex multicomponent raw materials. The paper presents the characterization of bauxite from several different deposits: Brazil, Milići, Čitluk and Kosovo. Chemical characteristics were determined by a combination of different analytical methods: gravimetry, potentiometric titration, atomic absorption spectroscopy (AAS) and UV-VIS spectrophotometry. Mineralogical composition was determined using X-ray diffraction and thermal analysis methods. Chemical and structural characterization is complemented by the results of scanning electron microscopy with EDX analysis. The information obtained was used for the assessment of the quality of investigated bauxites from the aspect of their application in the production of alumina.

Bauxites of different deposits were analysed for their content of TiO2 (mass %), using X-ray fluorescence spectrometry and the reference spectrophotometric method JUS B.G8.514. The samples were prepared in two ways: fusion with a borax technique and pressing, after which beads were formed for the purpose of analysis. Certified reference samples of bauxite were used for producing a calibration curve. The equation for calculating the content of TiO2 (mass %) in the samples of bauxite was derived from the calibration curve. Results of the XRF method were tested statistically by means of the F-test and the t-test (the standard sample of the bauxite and the reference method). The values obtained from the afore mentioned tests for the fusion beads showed that the XRF method was precise and correct and that there were no systematic errors, whereas for the pressed beads this method showed significant systematic errors.

The binary adsorption isotherms of volatile organic compounds (VOCs), and water vapor from the air have been the focus of much research in recent years. The content of adsorbed VOCs in the presence of water vapor can be determined by the volumetric or gravimetric method, in a static or dynamic mode. This study focuses on the adsorption technique in a static mode for isotherm measurement of the co-adsorption of VOCs and water vapor from the air using the gravimetric method. The content of VOCs is determined using a total organic carbon analyzer, while the amount of the adsorbed water was calculated from the difference between total adsorption (VOCs and water) and the adsorbed VOCs. This paper presents several adsorption isotherms with different VOCs (toluene, benzene, methanol, ethanol and isopropyl alcohol) and adsorbents (ZSM-5 zeolite, silica gel and Na-Form mordernite) in the presence of water vapor. The well-known adsorption isotherm models (Langmuir, extended Langmuir, Freundlich, extended Freundlich and Hill) were used to treat experimental results. The adjusted R-Squared (adj. R2) values obtained for those non-linear models for isotherms (total adsorpton (qe,tot) as a function of equilibrium concentration of VOC (Ce) and the adsorbed VOC (qe) as a function of equilibrium concentration of VOC (Ce) are used to determine the best-fit isotherm model. The modeling results showed that the 3-parameter models could fit the data better than the 2-parameter model, with relatively higher adj. R2. Experimental results demonstrate that the presented adsorption technique can be used for isotherm measurement of the co-adsorption of VOCs and water vapor from the air.

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