Arianit Reka

Diatomite is one of the most intensively examined raw materials in the materials industry with a broad range of various applications. The diatomite sample, collected from Vitačevo plateau in the vicinity of Kavadarci, was fully characterized by means of physical-mechanical, chemical, XRPD, SEM, TEM, DTA/TGA and IR techniques. The physical-mechanical features pointed out to soft, light, white to gray rock with shell-like structure exhibiting compressive strength from 4.65-4.88 MPa in dry form, whereas the total porosity ranges 70-72% and the density is 2.06-2.09 g/cm 3. The chemical analysis of the diatomite revealed that SiO2 content exceeds 91%. The results from the X-ray powder diffraction indicate predominant amorphous SiO2 phase associated with minor presence of crystalline quartz, muscovite, chlorites and plagioclase. The IR spectrum of the diatomite manifested characteristic bands for amorphous silica at 799 cm-1 and 1101 cm-1. DTA/TGA results display great thermal stability of the sample remaining amorphous up to 1050ºC whereas the SEM analysis determined the morphology, surface characteristics and the nanometric pores in the raw material. Thus, the studied diatomite is classified as a natural nanomaterial that is suitable for broad application in various construction materials, refractory ceramics, special oxide ceramics, and also finds potential use in filtering, adsorbent, catalysts, food and pharmaceutical industries.

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/cm 3 , total porosity of 61-63%, and specific gravity of 2.25 g/cm 3. The chemical composition is as follows: SiO 2, 86.03; Al 2 O 3 , 3.01; Fe 2 O 3 , 2.89; MnO, 0.06; TiO 2, 0.20; CaO, 0.76; MgO, 0.28; K 2 O, 0.69; Na 2 O, 0.19; P 2 O 5 , 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, mus-covite, 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 micro-scopy 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.

As important non-timber forest products, wild mushrooms provide diverse benefits, especially nutritional, medicinal and other socioeconomic benefits for ethnic groups located in NorthEast part of the Republic of North Macedonia. Ethno-mycological knowledge of most frequently used fungi was gathered from 32 inhabitants in 12 localities using in-depth interviews during April and November 2019. Each informant was asked about the local name of the fungus, its edibility, methods of preparation, habitat of growth, mode of consumption and medical use. A total of 33 species of wild mushrooms were cited. The results show that knowledge of useful mushrooms differs between two ethnic groups. The Macedonian ethnic group has the highest ethno-mycological expertise compared to Aromanian, which is expressed in their extensive cultural and practical use of fungi. On both ethnic groups man is more involved in harvesting and is the main holders of cultural aspects related to fungi. Despite the presence of edible ectomycorrhizal taxa in the research area, the two ethnic groups only seem to have an interest in saprotrophic taxa.

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 non-covalent 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.

Clayey diatomite is the local name for a mixture of diatomaceous earth and clay minerals. It represents a greyish, soft, very light, weakly cemented, fine biogenetic sedimentary rock. The studied material is taken from the vicinity of Bitola city (Republic of Macedonia). Here, clayey diatomite was treated up to three temperature intervals (800, 1000 and 1200oC) for a period of 1 hour. The X-ray powder diffraction results indicate the presence of both an amorphous phase and the following crystalline phases: quartz, feldspars (plagioclase), mica (muscovite) and chlorites. The results of SEM analysis revealed skeletons of alga Diatomeae with nano-pores. By thermal treatment of the samples, a gradual change in color as well as higher bulk density and compressive strength was observed. The increase of the temperature, in addition, affected the mineralogical composition and increased the presence of the amorphous phase (aluminasilicate glassy phase). SEM results of the thermally investigated samples depicted morphological changes expressed by shrinkage of the pore diameters in comparison to the initial material. The major and minor constituents were established by chemical analysis revealing the following chemical composition of raw clayey diatomite: SiO2 (63.65 wt%), Al2O3 (11.76 wt%), Fe2O3 (5.93 wt%), MnO (0.13 wt%), TiO2 (0.63 wt%), CaO (1.42 wt%), MgO (2.22 wt%), P2O5 (0.11 wt%), K2O (1.63 wt%), Na2O (0.92 wt%), LOI (11.50 wt%).

Extreme winter time air pollution episodes, fortify public concerns and put focus on air pollution as most important environmental problem in urban areas throughout the country. However, focused research efforts to derive information about pollution sources and the amount they contribute to ambient air pollution levels, are still missing, thus leaving room for dubious discussions and political, instead of scientifically based abetment strategies. Having in mind importance of proper information on air pollution sources and utilizing the data collected during several different measurement's campaigns performed for city of Skopje, as much extensive additional lab works and modeling efforts, indicative source apportionment analysis was performed for two sites (receptors) within Skopje urban area, one source specific (traffic) and one background site.

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 SiO2 (72.45%), high in alkali metal oxides (4.21 wt.% K2O, 3.56 wt.% Na2O), 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.

A B S T R A C T The aim of this study was to test the diatomaceous earth from a deposit near Rožden Village (Macedonia) as a raw material for low temperature hydrothermal production of porous ceramics. Hydrothermal synthesis of porous ceramics has been carried out under saturated steam pressure at 130 °C for a period of 1, 2 and 3 h. The objective of this work was to investigate the impact of slaked lime, autoclave curing time, autoclaving temperature and compaction pressure on the compressive strength and porosity of the products. During the hydrothermal synthesis, newly obtained calcium silicate hydrate dominates which give positive effect to the compressive strength and product porosity confirmed by X-ray powder diffraction. Moreover, a calcite was also evidenced by FTIR spectroscopy whose presence additionally increases the compressive strength of the hydrothermal products. The products obtained during the low-temperature hydrothermal reaction are classified as light porous ceramics with bulk density ranging from 0.71 to 0.91 g/cm 3 and compressive strength within 14.7–19.4 MPa.

The phase transformations of the amorphous SiO2 have a very important role in the application
of diatomite in the production of ceramic products. Therefore the phase transformations of diatomite are observed
with the use of DTA and TGA at temperatures up to 1100°C, and diatomite in powder state heated at temperature
1000–1200°C for a period of 1 and 2 hours. DTA and TGA analyzis show that during thermal treatment up to 1100°C
the diatomite remains in its amorphous phase. Roentgen-structural examinations of probes heated at 1000–1200°C for
a period of 1–2 hours show no presence of crystalline phases at 1100°C. XRD examinations of probes heated at
1200°C show presence of the crystalline phases cristobalite and quartz. The samples was heated at 1200°C for a period
of 2 hours, and was observed with an increase of the cristobalite content compared with quartz. SEM and TEM
examinations results of diatomite heated at 1200°C for a period of 2 hours show that the probes undergoes sintering
followed by reduced porosity.

A b s t r a c t: For the characterization of the natural amorphous SiO2 found in a new deposit in Republic of Macedonia, the following examinations were performed: physical-mechanical, chemical, mineralogical, SEM, IR and thermal examinations. Physical-mechanical analyses show that it is a white to grey colored rock, of low hardness, with a low volumetric mass and high porosity. Chemical analyses show that the material dominantly contains SiO2.
Mineralogical and XRD analyses show high percentage of isotropic amorphous mass content, with minimal contents
of submicroscopic cryptocrystalline mass. Thermal analyses show high thermal stability. Based on the conducted research
of the raw material from the new deposit, it can be concluded that it represents SiO2-diatomite of high quality,
useful for various purposes.

The aim of this research was to get a product, partially stabilized zirconia. The powders of partially stabilized zirconia were prepared from zirconium tetrachloride and hydrated yttrium  chloride  precursors  using  a  precipitation  method.  After  drying  and  calcination, the  powders were  examined  using  X-ray  diffraction.  X-ray  analysis  shows  that  the powder  dried  at  120ºC  is  in  amorphous  phase,  while  upon  calcination  at  800ºC,  it represents  a  partially  stabilized  zirconia  with  a  presence  of  cubic  and  monoclinic phases.  The  basic  purpose  in  preparing  such  mixtures  was  to  obtain  a  finally-dispersed  and homogenous powder which could be sintered at relatively low temperatures. From the super fine powder were prepared probes which were then dried at 120ºC and sintered at  temperature  of  1300ºC,  for  a  period  of  1  and  3  hours.  Further  analysis  of  the sintered probes showed density of 4.37 and 4.46 g/cm3.  The X-ray analyses show that these probes are represented with 70% of cubic phase and 30% of monoclinic phase, thus  concluding  the  partial  stabilized  zirconia.  Probes  sintered  at  1300ºC  were  tested to the resistance to the thermal shocks. The probes were heated at 1300ºC, for the time of 5 minutes and after that cooled at 20ºC, for the same time. All probes endured 40 thermal shocks without appearance of cracks. The probes don’t change their phase content, and have high thermal stability.

"""The aim of this paper is to present the physic-mechanical, chemical and mineralogical-petrographic examinations of the pumice and trepel. The pumice is from deposit site called Bojanciste, near Kavadarci, and the trepel deposit is from Suvodol near Bitola, Republic of Macedonia. The mineralogical-petrographic examinations of the pumice and pumicite have shown that the main component of the pumice and pumicite it is the volcanic glass, while in the crystal phase there is presence of albit, oligoclass, anorthit, microklin and in small quantities presence of quartz, biotit and augit. The examinations of the trepel have shown that it is a sedimentary rock (of biogenic origin) with greyish-white colour, very light and soft, porous and with fine to superfine grained structure. The trepel is composed mainly of opal as well as quartz, feldspar, illite and chlorites.
Keywords: raw materials, pumice, trepel, structural analysis"""

The aim of this research is to obtain light ceramic products from the reaction of diatomite with calcium hydroxide and trepel with calcium hydroxide. Diatomite is a loose, soft, porous, weakly bound rock with white to grayish color. Trepel is a natural mixture of diatomite and clay minerals. During the hydrothermal reaction of diatomite and trepel with calcium hydroxide new phases are formed. The newly formed phases are calcium silicate hydrates. The products obtained after the hydrothermal reaction are lightweight materials. Probes obtained from mixtures of trepel and calcium hydroxide have bulk density 0.85 g/cm 3 whereas the probes with diatomite and calcium hydroxide have bulk density 0.91 g/cm 3. The compressive strength of probes with trepel is 22.5 MPa while the compressive strength of probes with diatomite is 19.4 MPa.