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...
During mechanical activation, the energy of treated material is raised to a higher level that can lead to the chemical transformation of the activated material. This is the point that should be considered as a phenomenon of the mechanochemical transformations appearing as a result of mechanical activation. Sodium carbonate as a substance that is often subjected to mechanochemical synthesis was mechanically activated in this study. The subject was the monitoring of changes in the physico-chemical characteristics of sodium carbonate after exposure to different degrees of activation time within the range of 1-28 minutes. After activation, the samples were deposited in three environments, CO2, air, and vacuum, at room temperature, in a period of 64 days. The mass changes occurring during the treatment were measured depending on the processing environment. Increasing the mass was evident and was attributed to the chemisorption of moisture and carbon dioxide present in the air as a consequence of the sodium carbonate activation. The methods also used were calcimetric chemical analysis and X-ray structural analysis. According to obtained results, it was found that activated sodium carbonate is mass-transformed into sodium bicarbonate, whereby these changes are functionally dependent on activation time and the processing environment.
This paper presents the results of tests carried out to determine how the dosage of bentonite added as binder, affects the properties of green pellets made of the limestone fines that originate from Lithothamnium limestone processing. Bentonite was added to limestone in different mass fractions (1, 2.5, 5 and 10%), whereas all the other parameters of the pelletizing process remained constant. The aim of pelletizing was to consolidate limestone fines and form mechanically stable pellets, provided that all the other properties of limestone remain unchanged. The pellets formed in this way were analysed applying DTA/TG analysis and FTIR and SEM analyses. The results showed uniform distribution of bentonite in the pellets, demonstrated that the pellets are compact and there is no formation of new compounds. The pellets were tested for resistance to impact, compressive strength and abrasion resistance. Also disintegration tests were performed to determine the time required for the pellet to disintegrate completely in water. These mechanical properties are essential for transport, handling, storage and general use of pellets. The values of most of the parameters established for pellets with 5% bentonite, meet the standards required for use in agriculture for liming acid soils, however their application is limited because their impact resistance is unsatisfactory and the time required for their complete disintegration in water is extremely short. It should be noted that further increase of bentonite content (over 10%) will not improve the quality of green pellets. In view of the results obtained, it is necessary to introduce drying into the pelletizing process in order to bring the green pellets into solid state. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. TR-34013]
This study presents investigations of zeolitic tuff samples from the ?Igros- -Vidojevici? deposit. The aim of the research was to determine the quality of samples taken from all deposit parts. Thus, samples were taken from the footwall (?Zeolit 1?), and four samples from the central deposit part (?Zeolit 2?, ?Zeolit 3?, ?Zeolit 4? and ?Zeolit 5?). Characterization of the samples included chemical analysis, determination of the adsorption coefficient for methylene blue dye and cation-exchange capacity (CEC), X-ray powder diffraction analysis (XRPD), differential thermal and thermogravimetric analysis (DTA and TGA), and Fourier transform Infrared spectroscopic analysis (FTIR). Results have shown that the footwall consists mostly of clays, whereas zeolite minerals dominate in the rest of the deposit. XRD analysis of the ?Zeolit 1? sample confirmed presence of smectite and kaolinite clays, while zeolite of analcime type and quartz are present as smaller fractions. Chemical composition analysis and determination of heavy metal contents showed a significant amount (7.58%) of Fe2O3 in this sample. Therefore, further research can be pursued to find a method for removal of magnetic impurities in this deposit portion in order to utilize the clay fraction. On the other hand, according to XRD, FTIR, DTA/TGA and SEM/EDS analyses, samples which belong to the central deposit part (?Zeolit 2?5?) consist of clinoptilolite zeolite type, while clays are present in less than 10%. Thus, clays (smectites and kaolinite) accompanied with analcime and quartz are the most abundant footwall minerals while central deposit parts contain predominantly clinoptilolite accompanied with small amounts of clays. Mineragenetically, zeolites are most abundant in the ?Zeolit 2? and ?Zeolit 3? samples. The smallest value of CEC was determined for the ?Zeolit 1? sample (46.98 mmol/100g). According to CEC values determined for ?Zeolit 2? and ?Zeolit 3? (141.99 and 121.01 mmol/100 g, respectively) these samples are of the best quality, and could be utilized as adsorbents of inorganic pollutants from contaminated waters. Moreover, they could be potentially used for removal of mycotoxins from cattle feed. ?Zeolit 4? and ?Zeolit 5? samples have shown slightly lower CEC values (89.48 and 83.75 mmol/100 g, respectively), which implies lower quality, and, therefore, could be used for soil quality improvement. Finally, determination of the external CEC has revealed a significant difference between ?Zeolit 1? and ?Zeolit 5? samples (17.9 and 5.31 mmol/100 g, respectively). [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. TR34013 and Grant no. TR33007]
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