Browsing by Author "Petkov K."

Now showing 1 - 7 of 7
  • No Thumbnail Available
    Item
    A study of the partial neutralization process of solutions obtained during autoclave dissolution of pyrite concentrate
    (2017-01-01) Petkov K.; Stefanova V.; Stamenov L.; Iliev P.
    The process of the partial neutralization of solutions with high concentration of ferric ions and acidity (> 60g l-1 Fe3+ and H2SO4), obtained during autoclave dissolution of pyrite concentrate, has been studied. Two types of neutralizers have been used: limestone from deposit ore ``Velikan`` and a waste from cutting of marble plates - a fine and a coarse fraction. It was found that for the neutralization process limestone and the fine fraction from marble's waste can be used successfully. Both reactants are with a high content of calcium carbonate (> 92 %). The use of the coarse fraction of marble was inappropriate, due to the high content of magnesium carbonate (33.51 %) and the low extraction of gypsum (~ 49 %). The optimal parameters of neutralization process have been established: pH from 0.9 to 1.1, temperature 323K and time of neutralization 60 min. Gypsum, obtained under these conditions, has a high purity (< 0.05 % Fe, < 0.002 % Cu) and a high chemical activity. This makes it a suitable reactant for the conversion to ammonium sulfate, a commercial product that can be used as an artificial fertilizer.
  • No Thumbnail Available
    Item
    An analytical study of the neutralization process of solutions with high concentration of Fe(III) ions
    (2017-01-01) Petkov K.; Stefanova V.; Stamenov L.; Iliev P.
    With the means of software HSC Chemistry ver.7.1 modules: Equations Reaction and Eh-pH diagrams a thermodynamic assessment of the neutralization process of sulfuric acid solutions with high concentration of ferric ions (> 60 g l-1) with calcium carbonate and calcium hydroxide was carried out. Based on the calculated values of the energy of Gibbs and the equilibrium constants of the possible chemical interactions during the neutralization process with Ca(OH)2 and CaCO3 of a sulfuric acid solutions with a high concentration of ferric ions has been established that the neutralization process without participation of Fe3+ was thermodynamically more probable than in the presence of ferric ions. When Ca(OH)2 (hydrated lime) was used as neutralizer, the probability to obtain a precipitate of CaSO4*2H2O (gypsum) and FeO*OH (goethite) was the most thermodynamically probable, while using a neutralizer CaCO3 (limestone), the most probable was a precipitate of gypsum and Fe(OH)3. With increasing of the temperature from 25 to 60°C, the thermodynamic probability of goethite formation increases. Based on Eh-pH diagrams of the system H2SO4-CaCO3-Fe2(SO4)3-FeSO4-H2O it was established that in the pH range from -2 to 6 and temperature 25°C the most stable compound is calcium sulphate dehydrate. With the increase of temperature up to 60°C the most stable compound is anhydrite. The diagrams were built for molar concentrations of the elements in the solution (expressed as mol/kgH2O): 1,079 Fetotal, 0,622 S, 0,622 Ca and 0,622 C. The composition of the solution corresponds of the total iron and sulfuric acid concentrations and the quantity of CaCO3 necessary for neutralization of 100 % H2SO4. At the oxidation potential (Eh > 0.8 V) and high acidity of the solution (pH from -2 to 0.5), the areas of stability of iron ionic complex FeHSO4 2- and Fe3+ ion were found. In practice this means that the process of neutralization have to be carried out at a high oxidation potential and pH < 0.5 in order to avoid coprecipitation of iron sludge: Fe(OH)3 or FeO*OH.
  • No Thumbnail Available
    Item
    Compositional dependence of the optical properties of vacuum evaporated thin GeSe2-GeTe-PbTe films
    (2013-01-01) Petkov K.; Tasseva J.; Vassilev V.; Aljihmani L.
    Chalcogenide glasses from the GeSe2-GeTe-PbTe system were synthesized by taking preliminary prepared GeSe2, GeTe and PbTe in their molecular percentages and melting them in an evacuated quartz ampoule. Thin films were deposited on optical glass substrates BK-7 and Si-wafer substrates by thermal evaporation. Using X-ray microanalysis it was found that the film composition differs to a certain degree from the bulk composition. The changes in the optical properties of thin GeSe2-GeTe-PbTe films were studied as a function of their composition, exposure to light and annealing. It is shown by XRD analysis that the thin films are amorphous up to layers with composition of Ge27Se51Te14Pb8. The optical constants (refractive index, n and absorption coefficient, ), the thickness, d as well as the optical band gap, Eg, depending on the film composition were determined by spectrophotometric measurements in the region 450-2500 nm applying the Swanepoel's envelop method and Tauc's procedure. With the increase of the Te content in the layers, the absorption edge is shifted to the higher wavelengths, the refractive index increases from 2.54 for Ge 31Se66Te3 up to 3.37 for Ge32Se 55Te13 while the optical band gap decreases from 1.86 eV for to 1.30 eV for the same compositions. Similar dependence was observed with the increase of the PbTe content in the layers. After annealing of thin films, the values of n decrease, the optical band gap increases and a shift of the absorption edge to the shorter wavelengths is observed. © 2013 The Authors. Published by Elsevier B.V.
  • No Thumbnail Available
    Item
    Dry etching of thin chalcogenide films
    (2010-01-01) Petkov K.; Vassilev G.; Vassilev V.
    Fluorocarbon plasmas (pure and mixtures with Ar) were used to investigate the changes in the etching rate depending on the chalcogenide glasses composition and light exposure. The experiments were performed on modified commercial HZM-4 vacuum equipment in a diode electrode configuration. The surface microstructure of thin chalcogenide layers and its change after etching in CCl2F2 and CF4 plasmas were studied by SEM. The dependence of the composition of As-S-Ge, As-Se and multicomponent Ge-Se-Sb-Ag-I layers on the etching rate was discussed. The selective etching of some glasses observed after light exposure opens opportunities for deep structure processing applications. © 2010 IOP Publishing Ltd.
  • No Thumbnail Available
    Item
    Electrical conductivity, photoconductivity and gas sensitivity of Ge-Se-Te thin films
    (2012-01-01) Nesheva D.; Levi Z.; Raptis Y.S.; Raptis C.; Petkov K.; Vassilev V.
    Films of GexSeyTez (x≈33) with a thickness of 0.8 μm and four different compositions were prepared by thermal evaporation of preliminary synthesized glasses. The glass and film compositions were determined by Energy-Dispersive X-ray Spectroscopy. X-ray diffraction measurements have confirmed the amorphous structure of both bulk and thin film samples. The temperature dependence of the dark conductivity has been measured in the range 20 - 110 °C. No significant change of the room temperature conductivity (around 5x10-7 S/cm) and the dark current activation energy (around 0.7 eV) have been observed with increasing z. Spectral photocurrent measurements have revealed that the increase of Te content results in: (i) a photoconductivity decrease and (ii) a red shift of the low-energy side of the spectrum which indicates an optical band gap decrease. Resistive chemical sensing tests carried out at room temperature with ammonia, acetone, ethanol or water vapours in air as carrying gas have shown that the Ge32Se 55Te13 films are sensitive to ammonia but not to water vapour and hence they are suitable for selective ammonia sensors operating at room temperature. The observed sensitivity is related to the specific lattice structure of the region nearest to the film surface.
  • No Thumbnail Available
    Item
    Photo- and thermo-induced changes in optical constants and structure of thin films from GeSe2-GeTe-ZnTe system
    (2013-01-01) Petkov K.; Todorov R.; Vassilev V.; Aljihmani L.
    We examined the condition of preparation of thin films from GeSe 2-GeTe-ZnTe system by thermal evaporation and changes in their optical properties after exposure to light and thermal annealing. The results for composition analysis of thin films showed absence of Zn independently of the composition of the bulk glass. By X-ray diffraction (XRD) analysis it was found that a reduction of ZnTe in ZnSe in bulk materials takes of place during the film deposition. A residual from ZnSe was observed in the boat after thin film deposition. Optical constants (refractive index, n and absorption coefficient,α) and thickness, d as well as the optical band gap, E g, depending of the content of Te in ternary Ge-Se-Te system are determined from specrophotometric measurements in the spectral range 400-2500 nm applying the Swanepoel's envelope method and Tauc's procedure. With the increase of Te content in the layers the absorption edge is shifted to the longer wavelengths, refractive index increases while the optical band gap decreases from 2.02 eV for GeSe2 to 1.26 eV for Ge 34Se42Te24. The values of the refractive index decrease after annealing of all composition and Eg increase, respectively. Thin films with composition of Ge27Se 47Te9Zn17 and Ge28Se 49Te10Zn13 were prepared by co-evaporation of (GeSe2)78(GeTe)22 and Zn from a boat and a crucible and their optical properties, surface morphology and structure were investigated. The existence of a correlation between the optical band gap and the copostion of thin films from the system studied was demonstrated. © 2013 The Authors.
  • No Thumbnail Available
    Item
    Study of the crystallization process of ferric sulfate hydrate from rich of Fe(III) waste solutions
    (2017-01-01) Stamenov L.; Stefanova V.; Petkov K.; Iliev P.
    In present study the crystallization process of ferric sulfate hydrate - Fe2(SO4)3.xH2O from rich in Fe(III) sulfate waste solutions was investigated. These solutions were obtained after autoclave oxidation of pyrite concentrate. They are characterized with high concentrations (> 60 g l-1) of ferric ions and sulfuric acid. Based on the ternary diagram of the Fe2(SO4)3-H2SO4-H2O system and the laboratory tests the necessary compositions and conditions for preparation of saturated solutions for ferric sulfate crystallization process were determined. It was found that the crystallization process takes place with obtaining of bulky sludge containing following phases: FeH(SO4)2.4H2O (rhomboclase), Fe2(SO4)3.8H2O (ferric sulfate with eight molecules water) and Fe4.67(SO4)6(OH)2.20H2O (ferric sulfate hydroxide hydrate). After detention of the sludge for seven days at temperature 373 K two modifications of ferric sulfate hydrate were observed: ferric sulfate hydroxidehydrate(Fe4.67(SO4)6(OH)2.8H2O) and paracoquimbite (Fe2(SO4)3.9H2O).