Browsing by Author "Kazakova N."

Now showing 1 - 9 of 9
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    A study on the cementation process of non-ferrous metals from a brine leaching solution
    (2020-01-01) Kazakova N.; Lucheva B.; Iliev P.
    The initial solution obtained from brine leaching of zinc ferrite cake is used to study the cementation process of lead, silver and copper. The optimum parameters of the brine leaching stage are: NaCl concentration of 250 g/l, H2SO4 concentration of 5 g/l, a temperature of 60oC, and a pulp density of 12.5 %. Two series of experiments are carried out using different cementation agents-iron and zinc powders. The effects of the cementation agent consumption, the temperature, the time and the solution initial pH on the cementation metals degree are investigated. The results obtained show that the cementation with a zinc powder leads to higher cementation degree of silver, lead and copper indicating that the repeated use of the pregnant solution aiming to leach new portions from the zinc ferrite cake is most probably favored.
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    Modeling of biomass gasification
    (2014-02-25) Petkov V.; Mihailov E.; Kazakova N.
    Optimal conversion of chemical energy of the biomass or other solid fuel into the desired gas depends on proper configuration, sizing, and choice of gasifier operating conditions. Optimum operating conditions are often derived through trials on the unit or by experiments on pilot plants. Simulation, or mathematical modeling, allows the designer or plant engineer to reasonably optimize the operation or design of the plant. The good mathematical model can: find optimum operating conditions or a design for the gasifier, provide information on extreme operating conditions (high temperature, high pressure) where experiments are difficult to perform, provide information over a much wider range of conditions than those obtained experimentally, better interpret experimental results and analyze abnormal behavior of a gasifier, if that occurs. The equilibrium model is independent of the gasifier design which can make them more suitable for a system study of the most important process parameters. The use of an equilibrium model assumes that the residence time of the reactants in the gasifier is high enough to reach chemical equilibrium. For established biomass ultimate analysis, temperature of gasification air and temperature of produced gas, combining the mass balance equations with the equations for the equilibrium constants and equation of energy balance, the equivalence ratio (ER) and composition of produced gas can be obtained. A mathematical model for investigation of the influence of temperature of the produced gas and temperature of gasification air on the process parameters was developed. It can be used for estimation and design of gasification equipment.
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    MODELING OF H2SO4-NaCl LEACHING PROCESS OF ZINC FERRITE CAKE
    (2020-01-01) Kazakova N.; Lucheva B.; Iliev P.
    The behavior of the metals Ag, Cu, Pb and Zn upon H2SO4-NaCl leaching of zinc ferrite cake through modelling was studied. For this purpose, the SPAMA chemical equilibrium diagrams software was used. The systems Pb-Cl-SO4-H2O, Ag-Cl-SO4-H2O,Cu-Cl-SO4-H2O,Zn-Cl-SO4-H2O are modelled. The distribution of Pb, Ag, Cu and Zn spices in dependence of the chloride concentration, sulfate concentration, and ion strength are also considered. By means of the constructed Eh-pH and predominance diagrams of the considered systems, important details in H2SO4 - NaCl technological scheme for processing zinc ferrite cake are evaluated
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    Modelling of biomass pyrolysis
    (2015-01-01) Kazakova N.; Petkov V.; Mihailov E.
    Pyrolysis is an essential preliminary step in a gasifier. The first step in modelling the pyrolysis process of biomass is creating a model for the chemical processes taking place. This model should describe the used fuel, the reactions taking place and the products created in the process. The numerous different polymers present in the organic fraction of the fuel are generally divided in three main groups. So, the multistep kinetic model of biomass pyrolysis is based on conventional multistep devolatilization models of the three main biomass components - cellulose, hemicelluloses, and lignin. Numerical simulations have been conducted in order to estimate the influence of the heating rate and the temperature of pyrolysis on the content of the virgin biomass, active biomass, liquid, solid and gaseous phases at any moment.
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    OBTAINING Na2SO4 FROM SODA SMELTING SLAG FROM THE RECYCLING OF LEAD ACID BATTERIES
    (2024-01-01) Lucheva B.; Iliev P.; Kazakova N.; Stoinova I.; Iliev M.
    Soda smelting slag is generated during the processing of desulphurized paste from recycling of waste lead acid batteries and other lead containing secondary materials in tilting rotary furnaces, and it represents about 9.5 % of the mass of the charge entering the furnace. This type of slag is very reactive. It contains toxic substances (lead, arsenic and antimony) and because of the presence of alkaline compounds it is corrosive. In addition, it decomposes in contact with air, forming dust. Therefore, such hazardous product cannot be disposed without preliminary stabilization. The aim of the present work is to investigate the possibility for environmentally utilization of this slag. The conducted experiments have shown the possibility of extracting the sodium sulfate from the soda slag only by grinding in an aqueous medium with subsequent filtration. The resulting solution is subjected to sulfide purification from heavy non-ferrous metals and subsequent crystallization for obtaining a commercial product sodium sulfate. These processes could be easily implemented in companies that have applied Engitec’s technology for recycling spent lead-acid batteries and production of sodium sulfate from desulfurization of the lead paste. Implementation of these processes will eliminate the need for slag stabilization and prevent environmental problems.
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    OBTAINING Na2SO4 FROM SODA SMELTING SLAG FROM THE RECYCLING OF LEAD ACID BATTERIES
    (2024-01-01) Lucheva B.; Iliev P.; Kazakova N.; Stoinova I.; Iliev M.
    Soda smelting slag is generated during the processing of desulphurized paste from recycling of waste lead acid batteries and other lead containing secondary materials in tilting rotary furnaces, and it represents about 9.5 % of the mass of the charge entering the furnace. This type of slag is very reactive. It contains toxic substances (lead, arsenic and antimony) and because of the presence of alkaline compounds it is corrosive. In addition, it decomposes in contact with air, forming dust. Therefore, such hazardous product cannot be disposed without preliminary stabilization. The aim of the present work is to investigate the possibility for environmentally utilization of this slag. The conducted experiments have shown the possibility of extracting the sodium sulfate from the soda slag only by grinding in an aqueous medium with subsequent filtration. The resulting solution is subjected to sulfide purification from heavy non-ferrous metals and subsequent crystallization for obtaining a commercial product sodium sulfate. These processes could be easily implemented in companies that have applied Engitec’s technology for recycling spent lead-acid batteries and production of sodium sulfate from desulfurization of the lead paste. Implementation of these processes will eliminate the need for slag stabilization and prevent environmental problems.
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    Recovery of Iron, Silver and Lead from Zinc Ferrite Residue
    (2025-08-01) Iliev P.; Lucheva B.; Kazakova N.; Stefanova V.
    The present article aims to develop a technological scheme for processing zinc ferrite residue, which typically forms during the leaching of zinc calcine. This semi-product is currently processed through the Waelz process, the main disadvantage of which is the loss of precious metals with the Waelz clinker. The experimental results of numerous experiments and analyses have verified a technological scheme including the following operations: sulfuric acid leaching of zinc ferrite residue under atmospheric conditions; autoclave purification of the resulting productive solution to obtain hematite; chloride leaching of lead and silver from the insoluble residue, which was produced in the initial operation; and cementation with zinc powder of lead and silver from the chloride solution. Utilizing such an advanced methodology, the degree of zinc leaching is 98.30% at a sulfuric acid concentration of 200 g/L, with a solid-to-liquid ratio of 1:10 and a temperature of 90 °C. Under these conditions, 96.40% Cu and 92.72% Fe form a solution. Trivalent iron in the presence of seeds at a temperature of 200 °C precipitates as hematite. In chloride extraction with 250 g/L NaCl, 1 M HCl, and a temperature of 60 °C, the leaching degree of lead is 96.79%, while that of silver is 84.55%. In the process of cementation with zinc powder, the degree of extraction of lead and silver in the cement precipitate is 98.72% and 97.27%, respectively. When implementing this scheme, approximately 15% of the insoluble residue remains, containing 1.6% Pb and 0.016% Ag.
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    Sulfuric Acid Leaching оf Zinc Ferrite Residue
    (2026-01-01) Lucheva B.; Iliev P.; Kazakova N.; Stefanova V.; Ivanov H.
    Zinc ferrite residue, a by-product from the hydrometallurgical processing of zinc calcine, contains significant amounts of zinc, iron, lead, copper, and silver, often locked in complex oxide and spinel phases. This study aims to characterize zinc ferrite residue using ICP-OES analysis, XRD, and SEM/EDS, and to evaluate its behavior during sulfuric acid leaching under controlled laboratory conditions. Thermodynamic modeling with HSC Chemistry software was used to construct Eh–pH diagrams and predict phase stability across different temperatures and redox conditions. The experimental results confirmed efficient leaching of zinc, copper and iron, while lead and silver were largely retained in the insoluble residue. These findings highlight the potential for selective zinc extraction and concentration of lead and silver in the solid phase, offering a promising route for sustainable ZFR processing.
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    SYNTHESIS AND CHARACTERIZATION OF NANOPARTICLES FROM COAL FLY ASH
    (2024-01-01) Markov P.; Chernev G.; Nintianova D.; Kazakova N.; Karakostov H.
    In this study, amorphous nanoparticles were extracted from fly ash using a sol-gel method. The obtained nanoparticles were characterized using XRF spectroscopy, XRD, FT-IR and TEM. The XRD curves show the presence of both crystalline and amorphous phases. FT-IR analysis indicated the presence of silanol and siloxane groups. Upon analysis, the primary nanoparticles were found to exhibit a roughly spherical shape with an average size of approximately 65 nm. The findings of this study demonstrate the feasibility of applying the sol-gel method to synthesize nanoparticles derived from coal fly ash (CFA), thereby avoiding other expensive and energy-intensive methods of nanoparticle synthesis.