Petre Makreski

Visualization of a Discrete Solid-State Process with Steady-State X-ray Diffraction: Observation of Hopping of Sulfur Atoms in Single Crystals of Realgar

A molecular movie showing migration of a sulfur atom between molecules of realgar (alpha-As(4)S(4)) was obtained by a series of structure determinations of the dark stage of this all-solid autocatalytic reaction set.

Comparison of structural, textural and thermal characteristics of pure and acid treated bentonites from Aleksinac and Petrovac (Serbia)

Bentonite samples collected from vicinity of Petrovac and Aleksinac were treated with different sulfuric acid molarities. Acid attack dissolved the octahedral sheets by interlayer and edge attack. The effects of the H(2)SO(4) acid caused an exchange of Al(3+), Fe(3+) and Mg(2+) with H(+) ions leading to a modification of the smectite crystalline structure. The Mg and Fe substitution in the octahedral sheets promoted the dispersion of corresponding layers and formation of amorphous silicon. The activated bentonites, after the treatment of sulfuric acid, exhibited a lower cation-exchange capacity (CEC) and significant increase of specific surface area from 6 to 387 m(2) g(-1) (bentonite from Petrovac) and from 11 to 306 m(2) g(-1) (bentonite from Aleksinac). The acid reaction caused a splitting of particles within the octahedral sheet which led to an increase in specific surface area and decrease in CEC in both bentonites.

Minerals from Macedonia XXIII. Spectroscopic and structural characterization of schorl and beryl cyclosilicates.

IR and Raman spectroscopy study on two collected cyclosilicate species: schorl (from tourmaline group), Na(Fe,Mg)(3)Al(6)(BO(3))(3)Si(6)O(18)(OH,F)(4) and beryl (Be,Mg,Fe)(3)Al(2)Si(6)O(18) were carried out. Although beryl is nominally anhydrous mineral, vibrational results strongly indicate that H(2)O molecules exist in the structural channels. The number of vibrational bands and their frequencies revealed the presence of H(2)O type II, in which C(2) symmetry axis of the water molecule is parallel to the structural channel (and to the c-axis of beryl). On the other hand, it was found that observed bands in the IR and Raman OH stretching region of the other tourmaline varieties appear as a result of the cation combinations involving dominant presence of Mg and Fe cations in the Y structural sites. The strong indication derived from the vibrational spectroscopic results that the studied mineral represents a schorl variety, coincide very well with the results obtained by powder X-ray diffraction and X-ray microprobe analysis. Both minerals show IR spectral similarities in the region below 1500 cm(-1), whereas the resemblance between the Raman spectra (1500-100 cm(-1)) is less expressed confirming that these spectra are more sensitive to compositional changes and to structural disorder. The identification of both minerals was additionally supported by studying the powder X-ray diffraction diagrams.

Distribution of chemical elements in soils and stream sediments in the area of abandoned Sb–As–Tl Allchar mine, Republic of Macedonia

The aim of this study was to investigate the distribution of some toxic elements in topsoil and subsoil, focusing on the identification of natural and anthropogenic element sources in the small region of rare As-Sb-Tl mineralization outcrop and abandoned mine Allchar known for the highest natural concentration of Tl in soil worldwide. The samples of soil and sediments after total digestion were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Factor analysis (FA) was used to identify and characterize element associations. Six associations of elements were determined by the method of multivariate statistics: Rb-Ta-K-Nb-Ga-Sn-Ba-Bi-Li-Be-(La-Eu)-Hf-Zr-Zn-In-Pd-Ag-Pt-Mg; Tl-As-Sb-Hg; Te-S-Ag-Pt-Al-Sc-(Gd-Lu)-Y; Fe-Cu-V-Ge-Co-In; Pd-Zr-Hf-W-Be and Ni-Mn-Co-Cr-Mg. The purpose of the assessment was to determine the nature and extent of potential contamination as well as to broadly assess possible impacts to human health and the environment. The results from the analysis of the collected samples in the vicinity of the mine revealed that As and Tl elements have the highest median values. Higher median values for Sb are obviously as a result of the past mining activities and as a result of area surface phenomena in the past.

Theoretical and experimental study of the vibrational spectra of (para)symplesite and hörnesite

Arsenate water-bearing minerals, hörnesite (Alšar, Macedonia) and symplesite (Laubach, Germany), were studied by vibrational (IR and Raman) spectroscopy and X-ray powder diffraction. The observed vibrational spectra in both the high (1100-600 cm(-1)) and low (600-450 cm(-1)) wavenumber regions of AsO4 and H2O vibrations could be used to discriminate the two studied minerals. Spectral differences are especially pronounced in the bending and stretching regions of the H2O vibrations in the IR spectra. The observed bands in IR and Raman spectra were tentatively assigned. To support the assignment, IR spectra were theoretically simulated. These calculations were performed using the crystal structure of parasymplesite (no structural information of symplesite has been published so far) and hörnesite using a 3D periodic plane-wave pseudopotential density functional theory approach applying various combinations of exchange-correlation functionals. In this article, we report on the first experimental study of the vibrational spectra of the very rare symplesite mineral.

Determination of trace elements in iron minerals by instrumental and radiochemical neutron activation analysis

Abstract The method for determination of major and trace elements in iron oxide [hematite (Fe2O3)] and sulfide [pyrite (FeS2) and chalcopyrite (CuFeS2)] minerals using the k0-method of neutron activation analysis in both forms: instrumental (k0-INAA) and radiochemical (k0-RNAA) was suggested. In order to avoid interferences from iron on the determination of elements present in trace levels, radiochemical separation was made. Determination of the investigated elements in the aqueous phase was performed by k0-RNAA after extraction of iron by isoamyl acetate (IAA) and diisopropyl ether (DIPE) from hydrochloric acid solution. The distribution of 35 elements in extraction systems (with intermediate/medium and long half-lived radionuclides) present in the studied minerals was investigated.

Minerals from Macedonia. X. Separation and identification of some oxide minerals by FT IR spectroscopy, AAS, AES-ICP and powder XRD

The fourier transform infrared spectroscopy (FT IR), powder X–ray diffraction (XRD) as well as atomic absorption spectrometry (AAS) and emission atomic spectrometry with induced coupled plasma (AES-ICP) are used as powerful techniques in the process of identification of several oxide minerals (hematite, Fe 2 O 3; magnetite, Fe 3 O 4; limonite, FeOOH; goethite, α-FeOOH; corundum, Al 2 O 3; rutile, TiO 2; chromite, FeCr2O4 collected from various localities in the Republic of Macedonia. The mineral association of the localities where the minerals appear from (Pehcevo, Damjan, Alsar, Ržanovo, Sivec, Radusa, Veselcani, Kosino) with their petrological and mineralogical aspects are discussed. The content of the main and trace elements in the studied oxides is determined using AAS, AES-ICP, classical chemical analysis and the results are related to the geological and mineralogical conditions of their origin localities. As a pattern for mineral identification was the comparison of their infrared bands (their number, frequencies and intensities) with the corresponding literature data for the analogue (natural and synthetic) mineral species. In this context, in some cases disagreements between the infrared spectra of the studied mineral types (the number of bands and their frequencies) and the corresponding literature analogues appeared and have been discussed. The caused additional difficulties in the identification of the studied minerals were solved by the analysis of their X-ray patterns. Powder X-ray patterns were also representative for the detection of impurities in some of the studied mineral samples.

Determination of major and trace elements in iron-nickel-copper-cobalt ore reference materials using k0-NAA

Abstract The major and trace element contents in three iron-based ore reference materials were investigated using two methods of k0-based neutron activation analysis (k0-NAA): instrumental (k0-INAA) and radiochemical (k0-RNAA). To avoid interferences from iron in the determination of elements present at trace levels, a method using radiochemical separation was applied (k0-RNAA). Determination of the investigated elements by k0-RNAA in the aqueous phase from hydrochloric acid solution was performed after extraction of iron by diisopropyl ether (DIPE). It was found that Fe elimination lowered the limit of detection for some elements, thus enabling the determination of their content. The distribution of 39 elements (with intermediate/medium and long half-life radionuclides) present in the studied materials after Fe removal was investigated.

Theoretical and experimental study of the vibrational spectra of sarkinite Mn2(AsO4)(OH) and adamite Zn2(AsO4)(OH)

The arsenate hydroxyl-bearing minerals sarkinite and adamite were studied with vibrational spectroscopic (IR and Raman) and quantum theoretical methods. The observed IR bands in the higher (1100-600 cm(-1)) and especially lower (600-450 cm(-1)) frequency region of AsO4 vibrations could clearly discriminate between the studied analogues. The differences between their crystal structures are much pronounced in both IR and Raman OH-stretching regions. Namely, a single strong band is found in the case of orthorhombic adamite compared to four weaker bands observed in corresponding IR and Raman spectral regions of monoclinic sarkinite. Essentially all bands in the experimental spectra, collected at both room and liquid nitrogen temperature, were tentatively assigned. To support the tentative assignment of bands in the vibrational spectra of the mentioned minerals, periodic pseudopotential plane wave density functional theory calculations were carried out. Geometry optimizations of the 3D periodic systems included both optimizations of the atomic positions within the unit cell and of the unit cell itself. In most cases, the assignments were either supported or implied by the obtained theoretical data. It is worth mentioning that this is the first experimental and theoretical study of the vibrational spectra of the very-rare sarkinite mineral.

Adsorption of Acetochlor Herbicide on Inorganic- and Organic-Modified Bentonite Monitored by Mid-Infrared Spectroscopy and Batch Adsorption

The results of sorption of acetochlor herbicide with different concentrations (1–15 µg/mL) in inorganic- and organic-modified bentonite are presented. Acetochlor sorption in both bentonite types was studied by attenuated total reflectance spectroscopy in the mid-infrared region and by batch equilibrium method. Infrared spectroscopy results suggest that the interaction of acetochlor with inorganic (or organic) bentonite takes place by mechanism involving the carbonyl stretching vibration and phenyl ring in the acetochlor molecule. The increase of the acetochlor concentration results in red shift of both corresponding band wavenumbers. Batch adsorption study pointed out more expressed sorption of acetochlor in organic bentonite.