Browsing by Author "Lucheva B."
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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 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 Cyclic voltammetry investigations of hydrogen peroxide on Ag/Ni foam electrodes(2013-12-17) Stefanova V.; Lichev I.; Miletiev R.; Lucheva B.The main problem of the hydrogen peroxide fuel cells (HPFC) is to find out appropriate electro-catalytic materials for the electrodes. A possible solution is to use of Ni-foam. By deposition of suitable films onto the electrodes made of Ni-foam can be achieved a significantly increase of the chemical and corrosion stability, an electrocondutivity and a high catalytic activity. Moreover, a considerably decrease in the weight of the electrode and respectively its price with comparison to the massive metal can be also achieved. In the present work, the behavior of stabilized solutions of hydrogen peroxide with concentration 0.15M H2O2; 0.22M H2O2 and 0.45M H2O2 in alkaline medium (1M KOH) and synthesized by hydrolysis of CaO2.xH2O in the presence of KHCO3 peroxide solutions with concentration 0.42M H2O2 and1M KOH onto massive, Ag electrode and Ag/Ni-foam electrodes have been investigated by cyclic voltammetry. The thickness of the electrodeposited coating onto nickel foam was 5 and 30 μm respectively. On the basis of the present study it is established that silver shows a high catalytic activity during reduction process of HO2- ion in alkaline solutions. The electrochemical behavior of H2O2 onto silver film, electrodeposited on Ni foam is analogous to this onto massive silver. The silver coating behaves actively even after prollong (100 cycle) electrochemical treatment. The same behavior of synthesized solution of hydrogen peroxide as compared to the stabilized solution is established and this suggests a possibility for its direct use as reagent in hydrogen peroxide fuel cells.Item Effect of germanium on zinc electrowinning sulfate solutions(2014-02-25) Mehmed E.; Stefanova V.; Lucheva B.The basic method for the electrolyte zinc production is an electrowinning process based on sulfate solutions. The presence of the impurities in the electrolyte is a major problem for the zinc electrowinning industry. They decrease the current efficiency, increase the energy consumption and deteriorate the quality of cathode deposited zinc. In this work the influence of the concentration of germanium in the synthetic or industrial electrolyte from 0 to 3.17 mg/L and 0.04 to 3.21 mg/L respectively, without and in the present of antimony (4.95 mg/L) on zinc electrodepositing has been studied. For this purpose, two electrochemical techniques have been used: a cyclic voltammetry and a galvanostatic deposition. It has been established that the increase of germanium concentration in the zinc sulfate electrolyte above 0.05 mg/l leds to essential decreasing of hydrogen overpotential and intensive reverse anodic dissolution of zinc. The presence of germanium ions in the electrolyte, significantly decreases the current efficiency and the quality of the electrodeposited zinc. The harmful effect of germanium in the electrolyte is increased in the presence of antimony.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 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 Utilization of waste solutions of a high Fe(III) concentration by crystallization of ferric sulfate hydrate(2019-01-01) Stamenov L.; Stefanova V.; Lucheva B.; Atanasova-Vladimirova S.The study is focused on the utilization of waste solutions containing a high concentration of ferric ions and sulfuric acid (> 60 g L-1). It is found that the crystallization of ferricopiapite (Fe4.67(SO4)6(OH)2.20H2O), rhomboclase (Fe2(SO4)3. H2SO4.8H2O) and paracoquimbite (Fe2(SO4)3.9H2O) takes place after 70 % evaporation of the solutions and subsequent cooling to a room temperature. With increasing saturation of the solutions (75 % evaporation), the main phases identified in resulting crystals refer to hohmanite (Fe2(OH)2(SO4)2.7H2O) and rhomboclase (Fe2(SO4)3.H2SO4.8H2O). The crystals of paracoquimbite (Fe2(SO4)3.9H2O) and iron hydrogen sulfate hydrate (Fe2(SO4)3.H2SO4.2H2O) are obtained at crystallization temperatures of 100oC and 120oC. The main phases in the crystals change to oxonium iron bis sulfate ((H3O)Fe(SO4)2) and rhomboclase (Fe2(SO4)3.H2SO4.8H2O) with temperature increase to 200°C.