Browsing by Author "Iliev P."
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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.Item 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.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.Item Analytical study of the Waelz clinker dissolution in NH3 - (NH4)2SO4 system(2014-02-25) Draganova K.; Stefanova V.; Iliev P.; Lucheva B.In the NH3-(NH4)2SO4 system a thermodynamical analysis of dissolution process of the Waelz clinker, which is a waste product of zinc production, has been carried out. The analytical study has been executed by the help of a professional program HSC Chemistry Ver. 7.1 using both modules ``Reaction Equation`` and ``Eh - pH Diagrams``. The NH3-Fe-S-H2O, NH3-Cu-S-H2O and NH3-Ag-S-H2O systems describing the dissolution of iron, copper and silver compounds (oxides and sulfides) of Waelz clinker in an ammonia medium in the presence of ammonium salt (NH4)2SO4 have been investigated at various temperatures and pressures. The influence of temperature (25 and 110°C), pressure (atmospheric and 0.4 MPa) and the consumption of the reagents on the substance composition of the solutions has been defined on the basis of the calculated and constructed Eh - pH diagrams.Item Application of electron beam melting method for recycling of tantalum scrap(2024-10-01) Vutova K.; Stefanova V.; Iliev P.The paper presents a study on the refining efficiency of tantalum scrap when applying the electron beam melting method to recycle tantalum material. Thermodynamic analysis and experimental tests were carried out at different technological regimes to determine the optimal conditions for obtaining tantalum with high purity. The behavior of the controlled impurities (W, Nb, Mn, Ce, Cr, Mo, Al, Fe, etc) and the influence of the thermodynamic and kinetic technological parameters (temperature, melting time) on the refining efficiency of the studied material were investigated. At a temperature of 3700 K and a melting time of 10 min, the highest overall degree of refinement of 98.82% and the highest tantalum purity of 99.987% were achieved.Item Enhancing the energy and environmental efficiency of the fire refining of blister copper in anode furnace part I: Optimization of the heat generation in the operations area of the furnace(2018-01-01) Choshnova D.; Iliev P.The presented study provides useful information about the tendencies for optimization of the heat generation in the working area of the fire refining furnace of blister copper. A theoretical analysis of the possibility for replacing of the used fuel oil with natural gas is made. For the porpuses of the present study in house software product ``GOR`` of the Department of Physical Metallurgy and Heat Aggregates at the University of Chemical Technology and Metallurgy, Sofia, is used. The change of the theoretical combustion temperature of both fuels under different process conditions is studied. It is found that at combustion of natural gas with 2 % oxygen enrichment of the oxidation stream, values comparable to the theoretical combustion temperature of the fuel oil are achieved. The environmental effects from replacing of the fuels are exposed. The obtained results can be used to predict the change of the temperature field in the anode furnace when changing the conditions of its operation.Item Hydro - pyrometallurgical treatment of copper converter flue dust(2017-01-01) Lucheva B.; Iliev P.; Kolev D.The aim of this study is to investigate the possibility of pyrometallurgical recovery of lead and bismuth from preliminary desulfated copper converter flue dust into a metal phase, by carbothermal reduction in a soda ash smelt. Hydrometallurgical treatment of flue dust is actually caustic leaching and it aims to remove the sulfate sulfur. The desulfation degree of the converter flue dust, using 35 g NaOH per 100 g dust, is 80 % and the total impurities concentration in the Na2SO4 solution is below 50 mg l-1. The solid product from the hydrometallurgical step was subjected to pyrometallurgical treatment in a soda ash smelt. The effect of temperature, reducing agent type and amount, soda type and amount, on metal yield as well as the distribution of Pb, Bi, Cd, Ag and Cu among the process products, have been determined. It was found that with the increase of temperature, reducer and soda amounts the metal yield increased, but the copper and silver concentrations in the metal phase also increased. The laboratory experiments showed that it is possible to recover Pb and Bi a in separate product at a temperature of 900oC. The optimum established parameters for carbothermal reduction of desulfated copper converter flue dust are: temperature 900°C, soda amount 50 % of the dust mass, reducer amount 10 % of the dust mass and process duration 30 min. The recovery rates of lead and bismuth at these conditions are 80 % and 65 %, respectively. The obtained alloy consists of 74.87 % Pb, 12.96 % Bi, 0,22 % Cd and 11.63 % Cu. Semi industrial experiments should be carried out to clarify the optimal process parameters, since the furnace type and the method of charge heating will also influence the distribution of the metals among the products of smelting.Item 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 evaluatedItem 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.Item Purification of zinc containing Waelz oxides from chlorine and fluorine(2017-01-01) Iliev P.; Stefanova V.; Lucheva B.; Kolev D.The Waelz oxides (WO) obtained upon processing of zinc containing semi products in Waelz kilns are rich in impurities such as alkalines, chlorides and fluorides. After acid leaching of the WO chlorine and fluorine ions dissolve into the zinc electrolyte, causing corrosion of aluminum cathode and lead anode and sticking of the deposited zinc on the cathode. For normal production operation the WO must contain up to 1000 ppm chlorine and 100 ppm fluorine. In the present study the laboratory tests on alkaline scrubbing of zinc containing WO in sodium carbonate solutions are presented. The effect of sodium carbonate concentration, pulp density and test duration on the degree of fluorine and chlorine purification is investigated. Based on the conducted research it was established that at temperature 363 K, pulp density 300 g l-1, concentration of sodium carbonate 100 g l-1 and test duration 180 min, the final concentration of fluorine and chlorine in the treated WO is 90 and 220 ppm, respectively. WO with such concentration of impurities are appropriate for further processing for cathode zinc production.Item Recovery of copper and silver from Waelz clinker wasted from zinc production(2014-02-25) Lucheva B.; Iliev P.; Draganova K.; Stefanova V.Waelz clinker is a waste material from the processing of zinc-lead cake into Waelz furnace in Bulgarian metallurgical plant KCM Ltd, Plovdiv, which contains valuable components such as copper silver, iron and carbon. Previously the clinker was treated by sulfuric acid solution in order to remove iron. The residue which contains 3,8 % copper, 250 g t-1 Ag and 26 % C is an object of this experimental work. The purpose of the work is to investigate the silver and copper recovery from this residue using H2SO4-HNO3 solutions. The influence of dissolution time, temperature and concentration of nitric acid at constant sulfuric acid concentration on the silver and copper recovery degree were investigated. The maximum silver recovery degree - 95 % is achieved at the following conditions: process duration - 1 h; temperature - 90°C; sulfuric acid concentration - 1M; nitric acid concentration - 1M; pulp density - 10 %. At these conditions the copper is practically completely recovered. The remaining insoluble residue contains 0,02 % Cu and 22 g t-1Ag. A technological scheme for two stage processing of Waelz clinker is developed.Item Recovery Of gold from electronic waste by iodine-iodide leaching(2017-01-01) Lucheva B.; Iliev P.; Kolev D.Gold recovery by iodine-iodide solution is an effective and environment-friendly method. The aim of this research is to investigate the possibility of iodine-iodide gold recovery from gold-plated metal, which is a waste product of the electronic industry. Leaching experiments were carried out in solutions, containing 25 g l-1 iodine and 100 g l-1 KI, under room temperature, rotating speed of 500 rpm and mass ratio of 1:10. The degree of gold recovery for 1 minute leaching was 97,55 %. The concentrations of copper and nickel in the solution were about 0.05 g l-1, while the iron concentration was equal to that of the gold. It had been found that when gold concentration in the solution reached 1 g l-1, the iodine concentration decreased with 20 %. The optimal parameters of reducing dissolved gold iodide salts to gold metal are determined as 20 g KOH and 4 ml 10 % N2H4.H2O per one liter of the solution. Simultaneously with gold, iron and nickel almost completely precipitated (90 %), while the copper precipitation degree was around 25 %, because a large part of it precipitated as CuI during the leaching. The gold was separated from the precipitate by HNO3 treatment.The overall gold recovery is 94,56 %. Experiments were conducted to regenerate the solution by decreasing pH with H2SO4 and by adding of H2O2, as an oxidizing agent. The achieved regeneration degree was 80 %. The main disadvantage of iodine-iodide leaching is the great consumption of reagents and the need for a significant number of filtrations.Item Selective autoclave recovery of copper and silver from Waelz clinker in ammonia medium(2017-01-01) Iliev P.; Stefanova V.; Lucheva B.; Kolev D.Upon processing of zinc ferrite cakes in Waelz kilns a waste product, called Waelz clinker, is obtained. The copper and silver contents in this product are comparable to those of their ores which turns it into a valuable raw material. In the present work the experimental results on selective autoclave leaching of Waelz clinker in ammonia medium are presented. The effect of main technological parameters on the degree of value metals recovery and iron precipitation is studied. It is established that the highest extend of copper and silver recovery is obtained under the following conditions: temperature 383 K, Po2 0.4 MPa, ammonia concentration 110 g l-1, ammonium sulfate concentration 70 g l-1, pulp density 100 g l-1and test duration 120 min. At these conditions 86,5 % of copper and 68,5 % of silver are solubilized, whereupon over 99 % of iron is hydrolytically precipitated. The composition of the corresponding leach solution is: 1,22 g l-1Cu, 10 mg l-1 Ag, 90 mg l-1 Zn, 30 mg l-1 Fe and 40 mg l-1 Mn.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).Item Thermodynamic analysis of the sulphatization processes taking place in a dust-gas flow from flash smelting furnace(2016-01-01) Iliev P.; Stefanova V.; Shentov D.; Lucheva B.Analytical studies of the physicochemical interactions and isothermal equilibriums in Cu-Fe-S-O system were conducted at temperatures 1623K, 1373K and 973K by software HSC Chemistry ver.7.1 modules: Reaction Equations and Lpp diagrams. The thermodynamical stability of the phases in Cu-S-O and Fe-S-O systems were determined under certain conditions. The tendencies of their variation upon injection of ``sulphatizing air`` in the volume of the dust-gas flow output of flash smelting furnace (FSF) uptake were also studied. It was established that the formation of cuprum sulphate and iron ferric sulphate is thermodynamically possible only at temperatures lower than 973 K. The results predicted on the basis of the analytical investigation were confirmed by chemical and X-ray analyses of dust samples taken from the convective part of the waste heat boiler (WHB).Item TREATMENT OF COPPER FLUE DUST FROM FLASH FURNACE WASTE HEAT BOILER FOR IMPURITIES CONTROL(2024-01-01) Kadiyski M.; Angelov N.; Iliev P.; Stefanov E.; Semerdzhiev T.; Sopotenska I.During the pyrometallurgical processing of copper sulphide raw materials, part of the charge leaves the furnace space together with the exhaust gases in the form of dust entrainment. Volatile components also pass into the dust-gas flow, due to which it is enriched with impurities, some of which are harmful to the technological process. The formed dust-gas flow passes through dust collection equipment, where the main part of it is captured. Most often, the captured dust is recirculated, which leads to a decrease in the productivity of the furnace unit and a gradual increase in the content of impurities in the condensed products of the smelting. To overcome these disadvantages, it is necessary to take part or all the recirculating dust out of the melting cycle and process it independently to extract the valuable metals and dispose of the harmful substances. In metallurgical practice, industrial application for the processing of recirculating dust entrainment has mainly been accomplished by hydrometallurgical methods based on treating the flue dust in aqueous solutions of acid or alkaline reagents. In the present research work, laboratory results on hydrometallurgical leaching of flue dust from a flash furnace waste heat boiler (FF-WHB) are presented. The effect of the main technological parameters affecting the degrees of recovery of the main metals in solution was studied. Based on the experimental results, the optimal conditions for hydrometallurgical treatment of the FF-WHB flue dust were determined. By treating the dust under optimal conditions, the main tasks of the research are achieved - removal of impurities harmful to the technological process and reduction of the amount of flue dust processed in the flash furnace.