Browsing by Author "Grigorova D."
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Item Activity investigation of FeO, SiO2 and V2O5 in V2O5- FeO - SiO2ternary systems(2017-01-01) Grigorova D.; Paunova R.The activity of FeO, SiO2, and V2O5 in V2O5 - FeO - SiO2 ternary systems has been investigated. Pure oxides were used as reference mixtures, included in the system in ratios, analogous to those of mixtures, containing waste vanadium catalyst. Two mixtures were prepared: 1st mixture - V2O5 - FeO - SiO2 (pure oxides), 2nd mixture - waste vanadium catalyst - FeO - SiO2. The oxygen potential in the systems was determined by the EMF method. The solid electrolyte was ZrO2 (Y2O3), and the reference electrode - a mixture Mo/MoO2 in 1: 1 ratio, was used as a galvanic cell. The investigations were carried out in an isothermal and a non-isothermal condition. The Gibbs free energy and the activity coefficient were calculated from the experimentally obtained oxygen potential. Equations for ΔGT = f (T) were derived for different temperature ranges. New phases were observed in the mixture containing vanadium catalyst.Item Electric-arc-carbothermic processing of agglomerated waste dispersal materials from ferrous metallurgy(2014-01-01) Grigorova D.; Marinov M.; Paunova R.The present paper reports results referring to the production of pig iron under laboratory conditions using a low shaft electric furnace. Wastes from ferrous metallurgy subjected to a preliminary agglomeration are used as iron containing raw materials in the sintering charge. Material and heat balance calculations are carried out. It is found that sinters of high waste powders and sludge content can be used to give pig iron of low content of sulphur, phosphorus and non ferrous metals. The chemical composition, the yield and the specific energy consumption are found close to the existing standards.Item Kinetics of reduction of waste fayalite by calcium carbide(2019-01-01) Grigorova D.; Paunova R.Investigations of the slag, obtained from the non-ferrous metals, are of great importance to expand the raw material base for complex utilization, to increase the extraction of useful elements and to protect the environment. The kinetic of reduction of the waste fayalite by calcium carbide was investigated for two ratios of 1:1 and 1:10. Thermogravimetric analysis was carried out. Activation energy was determined, the maximum for the ratio 1:1 was 18.81 kJ/mol, and for ratio 1:10, Ea = 21.31 kJ/mol. The rate constant is also determined and the equations for the two defined temperature ranges were respectively derived. The maximum rate of reactions for the two mixtures is obtained, for the first mixture υ = 1,7176.10-3 mg/min at a temperature 1221 K, and for the second mixture the maximum rate is υ = 1.2339.10-3 mg/min at 1230 K.Item THERMODYNAMIC AND KINETIC INVESTIGATION OF IRON SILICATE REDUCTION WITH DIFFERENT REDUCING AGENTS(2022-01-01) Grigorova D.; Paunova R.The thermodynamics and kinetics of the reduction of iron silicate (fayalite), generated as a result of flotation processes in the production of copper concentrates, were studied. Three reducing agents were used - coke, charcoal, and graphite, in ratios to the stoichiometrically calculated amounts of reducer: 1: 1.5; 1: 2; 1: 2.5. The free Gibbs energy in the temperature range from 973 K to 1040 K was determined experimentally and the corresponding equations for 4G = f(T) were derived. The kinetic parameters were determined using thermogravimetric and differential methods at temperatures up to 1273 K. The results showed that the reduction process using coke went through three stages, and using charcoal - two stages. The reactions that took place were of the first order. Carbonated reduction of iron silicate occurred in the kinetic region. The highest values of the apparent activation energy were obtained as 67.83 kJ mol-1 when using coke (1257 K), and when using graphite - 60.29 kJ mol-1 at 1318 K. The lowest values of the activating energy 36 kJ mol-1 were observed with a charcoal reducer in the temperature range 966-1573 K.Item Thermodynamic investigation of briquette obtained from waste fayalite with calcium carbide(2017-01-01) Grigorova D.; Stoyanov D.; Paunova R.The iron content in fayalite, wasted from the copper production, is high and can be used as a raw material in the ferrous extractive metallurgy. This material has a fine dispersal structure, and it is necessary to be agglomerated for next refining processes. An experimental investigation for briquetting was carried out. X-Ray analysis of the initial sample showed fayalite and magnetite as main phases. Thermodynamics of the reduction of the fayalite using calcium carbide as a reductor was studied. Calcium carbide was used also as a regulator of the basicity of the charge. The experiments were carried out at ratios for fayalite - calcium carbide 1:1 and 1:10, relative to the stoichiometrically calculated quantity of calcium carbide, in the temperature range from 773 K to 1173 K. The oxygen potential, respectively Gibbs energy, has been calculated using EMF method with galvanic cell with solid electrolyte ZrO2 (Y2O3) and reference electrode Ni/NiO. Equations for DGT = f (T) for different temperature ranges were derived from the data experimentally obtained. The obtained briquettes were heat treated at temperatures 1125 K and 1423 K. The toughness, physical and mineral structure of the heated briquettes, were investigated. It was established that the melting temperature of the investigated mixtures decreased by increasing the amount of calcium carbide.Item THERMODYNAMIC STUDY OF SOLID-PHASE REDUCTION OF POLYGRADIENT IRON-CONTAINING MATERIAL(2022-01-01) Grigorova D.; Paunova R.The studied iron ore material is a polygradient with increased content of manganese, barium, and lead. The thermodynamics of the reduction of this pelletized material, using the Electromotive force (EMF) method, has been investigated. Coke breeze and brown coal/lignite were used as reducing agents. The solid reducer was added in two ways - into the charge for the production of raw pellets and in the layer of the pellets and reducer, i.e. outside the pellets. The effects of pellets reduction and the ongoing temperature-dependent reduction processes were performed experimentally. Based on the experimental data, the equations Δ = f(T) of the studied pellets were derived. The stages of pallets heating, when the main solid-phase interactions and the possible reduction processes take place, were described. It was found out that, in the temperature range 933 K - 1213 K, the reduction of hematite to magnetite takes place as a priority. The barium and lead oxide are completely reduced. The macrostructure and phase changes were observed metallographically. The results showed that when adding the reducer into the composition of the pellets, up to 90 % degree of metallization was reached.Item Utilization of waste powder and sludge in iron ore sintering process(2014-01-01) Grigorova D.; Tsanev T.; Marinov M.Extraction metallurgy is characterized by low rate waste emissions utilization. The greater part of the dust and sludge generated by the gas cleaning facilities does not return to production. Their accumulation leads to ecological problems. The present study treats theoretically calculated and experimentally obtained series of sinters of various basicity and concentrations of sludge and waste mixture. The latter contain sinter powder, blast furnace powder, convertor dust and electric arc furnace powder of a ratio corresponding to that yearly observed under real production conditions. The main characteristics of the sintering process are established. The results reveal that the main characteristics of sintering process do not significantly change in case of using waste powders and sludge.