Browsing by Author "Stamenov L."
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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 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 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 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.