In understanding the catalytic efficacy of silver (Ag0) and gold (Au0) nanoparticles (NPs) on glass-ceramic (GC) crystallization, the microstructure–machinability correlation of a SiO2–MgO–Al2O3–B2O3–K2O–MgF2 system is studied.

The physico-mechanical, chemical and mineralogical characteristics of volcanic glass (perlite) from the Mariovo region (Macedonia) as well as the mineralogical changes that occur during its thermal treatment were investigated to demonstrate its utilization for industrial use. The native perlite was characterized by chemical analysis, X-ray powder diffraction (XRPD), infrared (IR) spectroscopy, thermal analysis (TGA/DTA), scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM), and solid-state NMR. The chemical examination suggests that the perlite represents an acidic volcanic rock with a high percentage of SiO 2 (72.45%), high in alkali metal oxides (4.21 wt.% K 2 O, 3.56 wt.% Na 2 O), with a loss of ignition 3.54 wt.%. Results from the XRPD indicated major amorphous behaviour, with low amounts of feldspars, quartz, and cristobalite. SEM examinations revealed glassy structure with presence of certain pores (dimensions ranging from 50-100 μm). The determined expansion coefficient was 20 times its original volume. XRPD of expanded perlite compared to the native perlite depicted new intensive peaks of cristobalite. SEM and TEM revealed irregular morphology with broken or ragged edges. On the basis of the chemical and mineralogical composition, the studied perlite is classified as an appropriate material suitable as ceramic flux to lower the sintering temperature.

The diatomaceous earth (DE), collected from the Mariovo region in North Macedonia, was characterized and thermally modified. The material represents a sedimentary rock of biogenic origin, soft solid that can be easily disintegrated, with white to grayish color, with bulk density of 0.51–0.55 g/cm3, total porosity of 61–63%, and specific gravity of 2.25 g/cm3. The chemical composition is as follows: SiO2, 86.03; Al2O3, 3.01; Fe2O3, 2.89; MnO, 0.06; TiO2, 0.20; CaO, 0.76; MgO, 0.28; K2O, 0.69; Na2O, 0.19; P2O5, 0.15; and loss of ignition, 5.66 (wt%). The mineralogy of the raw DE is characterized by the predominant presence of amorphous phase, followed by crystalline quartz, muscovite, kaolinite, and feldspar. Significant changes in the opal phase are observed in the 1,000–1,200°C temperature region. At 1,100°C, the entire opal underwent solid–solid transition to cristobalite. Further ramp of the temperature (1,100–1,200°C) induced formation of mullite. Scanning electron microscopy (SEM) and transmission electron microscopy depict the presence of micro- and nanostructures with pores varying from 260 to 650 nm. SEM analysis further determined morphological changes in terms of the pore diameters shrinkage to 120–250 nm in comparison to the larger pores found in the initial material. The results from this investigation improve the understanding of mechanism of silica phase transition and the relevant phase alterations that took place in DE upon calcination temperatures from 500 to 1,200°C.

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Abstract:Natural minerals from different localities in the Republic of Macedonia are selected for elimination of Cr(VI) ions from water resources. For that aim are selected: aksil (Kriva Palanka), trepel (Bitola), SiO 2 amorphous (Kozuf), pemza (Bojanciste). In this study, their adsorption capacity is analyzed using spectrophotometric method (UV/VIS Spectrophotometer). Results from the spectrophotometric analysis in all used examples gave us insight for the starting concentration of Cr(VI) before adsorption and concentration after adsorption. The physical, chemical and mineralogical characteristics of adsorbents are studied. XRD, TGA-DTA and FT-IR analysis are used for characterization of natural mineral materials. The surface area of the sorbents were measured by BET method. With aim to determine the optimum pH value for maximal removal of Cr(VI) ions, the point of zero charge, pH PZC , for investigated materials were obtained. The aim of the study is to select which adsorbent is more effi cient for elimination of Cr(VI) from water resources. According to obtained results all of them were successful in elimination of Cr(VI), but more effi cient and economic is trepel.

This study is focused on the adsorption of hexavalent chromium ions Cr(vi) using graphene oxide (GO). The GO was prepared by chemical oxidation (Hummers method) of graphite particles. The synthesized GO adsorbent was characterized by Fourier transform infrared spectroscopy and UV-Vis spectroscopy. It was used for the adsorption of Cr(vi) ions. The theoretical calculations based on density functional theory and Monte Carlo calculations were used to explore the preferable adsorption site, interaction type, and adsorption energy of GO toward the Cr(vi) ions. Moreover, the most stable adsorption sites were used to calculate and plot noncovalent interactions. The obtained results are important as they give molecular insights regarding the nature of the interaction between GO surface and the adsorbent Cr(vi) ions. The found adsorption energy of −143.80 kcal/mol is indicative of the high adsorptive tendency of this material. The adsorption capacity value of GO toward these ions is q = 240.361 mg/g.

The development of low-cost adsorbent coal FA (Kosovo A) for pesticide removal is an important area of scientific research. With this study, we show the potential of adsorption of coal FA (Kosovo A) for the removal of benalaxyl and atrazine from water. We have found that the amount of adsorbed benalaxyl and atrazine increases with an increasing amount of coal FA (Kosovo A) in solution. The maximum capacity coal FA (Kosovo A) to adsorb benalaxyl and atrazine was found to be 0.46 and 0.45 mg/g according to the Freundlich equation and 3.48 and 3.33 mg/g according to the Langmuir equation. The Freundlich adsorption equation better explains the adsorption results of pesticides (benalaxyl and atrazine) in coal FA (Kosovo A), as the values of the recovery coefficient (R2) were higher in Freundlich equation than the Langmuir equation. The adsorption isotherms were of type L and show that the adsorption efficiency of the coal FA (Kosovo A) depends on the initial concentration of benalaxyl and atrazine in solution and the maximum removal of benalaxyl and atrazine was achieved at concentrations less than 10 µg/ml. This study’s results are expected to have implications for the use of coal FA (Kosovo A) for the removal of pesticides from water.

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