In this study, a mixture of magnesium oxide and titanium dioxide was mechanically activated in order to investigate the possibility of mechanochemical synthesis of magnesium titanate. Mechanical activation was performed for 1000 min in a high-energy vibro mill (type MH954/3, KHD Humboldt Wedag AG, Germany). The mill is equipped with housing having a horizontally placed shutter. The cylindrical stainless steel working vessel, with inner dimensions of 40 mm in height and 170 mm in diameter, has working elements consisting of two free concentric stainless steel rings with a total weight of 3 kg. The engine power is 0.8 kW. Respecting the optimal amount of powder to be activated of 50-150 g and the stoichiometric ratio of the reactants in the equation presenting the chemical reaction of magnesium titanate synthesis, the starting amounts were 20.2 g (0.5 mol) of MgO and 39.9 g (0.5 mol) TiO2. During the experiments, X-ray diffraction analysis of the samples taken from the reaction system after 60, 180, 330, and 1000 min of mechanical activation was performed. Atomic absorption spectrophotometry was used for chemical composition analysis of samples taken at different activation times. Based on the X-ray diffraction analysis results, it can be concluded that the greatest changes in the system took place at the very beginning of the mechanical activation due to the disturbance of the crystal structure of the initial components. X-ray diffraction analysis of the sample after 1000 min of activation showed complete amorphization of the mixture, but diffraction maxima characteristic for magnesium titanate were not identified. Therefore, the mechanical activation experiments were stopped. Evidently, the energy input was not sufficient to overcome the energy barrier to form a new chemical compound - magnesium titanate. The failure to synthesize magnesium titanate is explained by the low negative Gibbs energy value of -25.8 kJ/mol (despite the theoretical possibility that the reaction will happen), as well as by the amount of mechanical energy entered into the system during activation which was insufficient to obtain the reaction product. Although the synthesis of MgTiO3 was not achieved, significant results were obtained which identify models for further investigations of the possibility of mechanochemical reactions of alkaline earth metals and titanium dioxide.
The influence of sized zeolite product range on the ability of adsorption has been studied by numerous researchers. Research in this area has mostly concentrated on natural zeolite, production results that can be used in the application of zeolite products for animal feed or water purification. Researchers use the following range of size classes for this purpose: powder, -5 +2 mm, -2 +0.5 mm, -2 +0 mm, -2.4 + 1.4 mm, -1.4 +0.4 mm, -0.4 +0 mm, -0.1 +0 mm, -0.8 +0.6 mm, -0.5 +0 mm, -0.5 +0.315 mm, -0.15 +0.075 mm, -0.090 +0.063 mm, -0.5 +0.1 mm, -0.1 +0.04 mm; -+0 0.63 mm, -0.2 +0 mm, -0.043 +0 mm, -0.1 +0.063 mm. In the paper entitled "Structural and Physico-chemical Properties of Natural Zeolites: Clinoptilolite and Mordenite", the fractions of clinoptilolite with the particle size ds = 0.355-0.5 mm and mordenite of ds = 0.2-0.315 mm were chosen for examination (Korkuna et al. 2006). For studying the adsorption of arsenic (V) from a water solution onto a surfactant-modified zeolite, the authors Mendoza- Barron et al. (2011) used modified natural zeolite from the deposit located in San Luis Potosi, Mexico. The sample was ground and sieved to an average particle size of 0.42 mm . Natural clinoptilolite zeolite from the Donje Jasinje deposit was used in three size classes: -0.5 mm, -2 +0.5 mm and -5 +2 mm, in the paper "Kinetics and Thermodynamics Study of Copper Li et al. (2009) investigated the adsorption of chromates on natural zeolite by the modified surfactants. They used the following zeolite fractions: 3.6-4.8 mm, 1.4-2.4 mm and < 0.4 mm. It was confirmed that adsorption of chromates increases with a decrease in zeolite particle size. Despite the fact that with an increase in particle size the adsorption of a specific pollutant decreases, it was also pointed out that larger particle size is required in order to achieve better hydraulic properties, and that, due to this fact, it is important to examine the effects of particle size on adsorption of the specific pollutant. Unlike most of the clay minerals and their property of swelling in water, zeolites have tighter three-dimensional crystal structure, and thus hydraulic properties that enable a wider range of applications in purifying contaminated water (Huggerty et al. 1994; Zhaohui Li et al. 1997; Sheng et al. 1997). Due to the inverse proportionality between the grain size and specific surface in the adsorption experiments with various contaminants in natural zeolite, it is necessary to test the effect of grain size on adsorption the specific contaminant (Lemiae 2006).If too low a cation exchange capacity (CEC) value of the ground class -0.1 +0 mm sample is obtained, after crushing the starting sample to the class -3 +0 mm, the classification can be applied and then the class -0.1 +0 mm with satisfying CEC value can be separated. A higher CEC value can also be obtained from the rest of the classification, i.e. in the +0.1 mm class, and grinding of that class will provide the desired quality of the class -0.1 +0 mm. Therefore, testing the zeolite quality...
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