Metallurgy of ferroalloys
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Metallurgy of ferroalloys

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The file entails mining, extraction and usage of various ferro-alloys worldwide

The file entails mining, extraction and usage of various ferro-alloys worldwide

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Metallurgy of ferroalloys Metallurgy of ferroalloys Document Transcript

  • qwertyuiopasdfghjklzxcvbnmq wertyuiopasdfghjklzxcvbnmqw ertyuiopasdfghjklzxcvbnmqwer tyuiopasdfghjklzxcvbnmqwerty FERROALLOYS PRODUCTION uiopasdfghjklzxcvbnmqwertyui opasdfghjklzxcvbnmqwertyuiop asdfghjklzxcvbnmqwertyuiopas dfghjklzxcvbnmqwertyuiopasdf ghjklzxcvbnmqwertyuiopasdfgh jklzxcvbnmqwertyuiopasdfghjkl zxcvbnmqwertyuiopasdfghjklzx cvbnmqwertyuiopasdfghjklzxcv bnmqwertyuiopasdfghjklzxcvbn mqwertyuiopasdfghjklzxcvbnm qwertyuiopasdfghjklzxcvbnmq wertyuiopasdfghjklzxcvbnmqw ertyuiopasdfghjklzxcvbnmrtyui PREPARED BY: MOFOKENG L.A STUDENT NO.: 201214830
  • TABLE OF CONTENTS 1. Fire Refining Processes 1.1. Cupellation 1.2. Liquation 1.3. Distillation 1.4. Oxidation 1.5. Chlorination 2. Ferroalloys 2.1. Ferrochrome 2.2. Ferrosilicon 2.3. Ferromanganese 2.4. Ferrovanadium 3. References Page 1 of 11
  • 1. FIRE REFINING PROCESSES Cupellation Cupellation is a metallurgical process in which ores or alloyed metals are treated under high temperatures and carefully controlled operations in order to separate noble metals, like gold and silver, from base metals like lead, copper, zinc, arsenic, antimony or bismuth that might be present in the ore. This process is based on the principle that precious metals do not oxidise or react chemically, contrary to what happens to the base metals; so that when they are heated at high temperatures, the precious metals remain apart and the others reacts forming slags or other compounds. In this process the impure metal is heated in a blast of air when impurities are oxidised and blown away. Liquation Liquation is a metallurgical process for separating metals from an ore or alloy. The material must be heated until one of the metals starts to melt and drain away from the other and can be collected. This process is used for refining easily fusible metals like lead and tin. The impure metal is heated on the sloppy hearth of an electric furnace. The metal melts and flows down leaving the impurities. In this process the metals are melted and made to go into the liquid state. Metals that have low melting points such as lead, tin and others can be purified by this method. A sloping hearth of a furnace is used on which the metal is placed and melted. The temperature of the furnace is maintained slightly above the melting point of the metal. Due to the heat the pure metal melts and flows down, leaving behind infusible impurities having higher melting point. Figure 1: Schematic Presentation of Liquation Refining Page 2 of 11
  • Distillation Distillation is a process whereby liquefied metals are separated based on their extensive properties. The melting point is the property which is used more often. This Refining Process is based on the principle that different metals or alloys have differing melting point due to their composition and atomic structure. Some metals have very low melting point and soon vaporize on behind heating, while the associated impurities remains in the solid state. Zinc, mercury and arsenic are purified by this method. Refining of volatile metals like mercury, zinc etc. is done by distillation. The impure form of these metals can be distilled to get their vapours, which are then condensed to get the pure metal. The metal to be refined is heated above its boiling point when the impurities do not vaporize. Pure metal vapourises and is condensed while the impurities are left behind. Oxidation Oxidation is a process whereby impurities are removed from impure metals by passing calculated amount of oxygen through the molten metal. This Refining method is based on the principle that impurities or unwanted substances are most often oxidized easily than the wanted metal. Sometimes impurities are able to get oxidized more easily than the metal itself. In this case oxidative method is used. For example if impurities are S, C, Si or P, they can get oxidized more easily than the metal itself. For example in case of pig iron Fe, these non-metals are present as impurities. When air is passed over hot molten pig iron, these non-metals get oxidized to CO2, SO2, P2O5 and can be removed easily. This process is used when the impurities have a greater affinity for oxygen than the metal itself. This method is usually employed for refining the metals like Fe, Cu, Ag, etc. The oxidation is done by various ways. Impurities of sulphur, carbon, phosphorous etc. can be removed from the impure metals by passing calculated amount of oxygen or air through the molten metal. These impurities get oxidized to gaseous products like sulphur dioxide,carbon dioxide, phosphorous (V) oxide respectively. These then escape out from the metal. Page 3 of 11
  • Chlorination The process involves blowing a stream of chlorine gas over and through a crucible filled with molten impure metal. Impurities in the metal form chlorides before the metal does and these insoluble salts are removed from the melt by skimming the surface. The process is based on the contact of metal oxides or sulphides with chlorine or hydrogen chloride in reversible reactions. The oxides for which the Gibbs free energy of the reactions has large negative values, for example, PbO, ZnO, and Ag2O, are chlorinated at low concentrations of chlorine in a gaseous medium containing oxygen. The oxides with large positive values of the Gibbs free energy, such as SiO2, TiO2, and A12O3, display virtually no reaction with chlorine gas, since the presence of even minute amounts of oxygen in the gaseous medium inhibits the formation of chlorides. The chlorination of oxides is facilitated in the presence of substances that take up free oxygen and reduce its concentration in the gas phase, such as carbon, hydrogen, and sulphur dioxide. Thus, by changing the composition of the gas phase and the temperature of the process, it is possible to choose the conditions for selective chlorination; specifically, in the presence of oxygen and water vapour it is possible to chlorinate a number of nonferrous metals while keeping iron in the form of an oxide, whereas in a reducing atmosphere the iron oxides are converted into chlorides. Chlorination can be carried out by roasting, chloridation, or separation. Chlorination by roasting is conducted at relatively low temperatures, leading to the formation of non-volatile chlorides. It is achieved in electric furnaces, fluidized-bed furnaces, tube furnaces, or multiple-hearth roasting furnaces During the refinery of Gold in the Miller process chlorination is usedwhereby chlorine and silver combine with base metals to form chlorides, while gold is left untouched by this. Doré bars are melted in a furnace and then chlorine is added to form chlorides. After a few hours, the chlorides are removed from the heat and skimmed away, leaving just the gold, which can be poured into moulds.Chlorination is also used to remove impurities from molten metals, for example, sodium and calcium from aluminum, zinc from lead, and lead from tin. Work is under way to develop methods of recovering copper and cobalt from nickel converter matte by means of chloride melts Page 4 of 11
  • 2. FERROALLOYS Ferroalloys are alloys with iron employed to add chemical elements into molten metal, usually during steelmaking. Ferroalloys impart distinctive qualities to steel and cast iron or serve important functions during production and are, therefore closely associated with the iron and steel industry, the leading consumer of ferroalloys. The leading ferroalloys producing countries in are, in decrease order in production, China; South Africa; Russia; Kazakhstan and Ukraine. Ferrochrome Description Ferrochrome (FeCr) is an alloy of chromium and iron comprising between 50% and 70% chromium. The ferrochrome is produced by electric curve melting of chromite, an iron magnesium chromium oxide and the most important chromium ore. South Africa is one of the countries which produce most Tons of Ferrochrome in the world. The production of steel is the largest consumer of ferrochrome, especially the production of stainless steel with chromium content of 10 to 20% is the main application of ferrochrome. Mining Ferrochrome is formed from Chromium and iron, the chromium used in making ferrochrome is extracted from chromium ore called Chromite. Chromite deposits are mined by both underground and surface techniques. Much of the ore is rich enough to be used directly: for production of ferrochromium, a rich, lumpy ore containing more than 46 percent Cr2O3 and having a chromium-iron ratio greater than 2:1 is preferred, but ores with a lower ratio and as little as 40 percent Cr2O3 are also used. As finely divided ores, which do not smelt efficiently, come under greater exploitation, a number of processes are employed to agglomerate them for more satisfactory use in furnaces. Fines can be blended with fluxes and coke and then preheated or “pre-reduced” before being charged into an electric smelting furnace Extraction, Processing band Production Ferrochrome extraction and production is basically a carbothermic reduction process taking place at high temperatures. Cr Ore (an oxide of chromium and iron) is reduced by coal and coke to form the iron-chromium alloy. The heat for this reaction can come from several forms, but typically from the electric curve formed between the tips of the electrodes in the bottom of the furnace and the furnace fireside. This curve creates temperatures of about 2,800 °C. In the process of smelting, huge amounts of electricity are consumed making production in countries with high power charges very costly.Tapping of the material from the furnace takes place intermittently. When enough smelted ferrochrome has accumulated in the hearth of the furnace, the tap hole is drilled open and a stream of molten metal and slag rushes down a trough into a chill or ladle. The ferrochrome solidifies in large castings, which are crushed for sale or further processed.Ferrochrome is often categorized by the amount of carbon and Page 5 of 11
  • chrome it contains. The vast majority of FeCr produced is charge chrome from Southern Africa. With high carbon being the second largest section followed by the smaller subdivisions of low carbon and intermediate carbon material.The major Producer or supplier of Ferrochrome in South Africa is EXSTRATA ALLOYS followed by HERNIC which is also based in South Africa and is the world’s 4th largest producer of ferrochrome and lastly SAMANCOR. Uses and other Properties Ferrochrome is used as carbon high ball steel, steel and the high alloy agent, improving steel its quench-hardening ability, increase steel abrasion resistance and hardness. The other use of Ferrochrome is that it is used as a cast iron additive, improve the wear resistance of cast iron and improve the hardness, also make the cast iron that has good heat resistance. Other minor uses include being used as power needed to production of metallic chromium containing Cr raw materialsand for oxygen blowing method of stainless steel smelting raw material Ferrosilicon Description Ferrosilicon is a ferroalloy, an alloy of iron and silicon with average silicon content between 15 and 90 weight percent. It contains a high proportion of iron silicides. Mining Silicon which is used in the production of ferrosilicon along with iron is mined in the form of Silicon Dioxide. Silicon compounds are the most significant component of the Earth’s crust. Silicon is recovered from an abundant resource: sand. Most pure sand is quartz, silicon dioxide (SiO2). Since sand is plentiful, easy to mine and relatively easy to process, it is the primary ore source of silicon. Some silicon is also retrieved from two other silicate minerals, talc and mica. The metamorphic rock, quartzite, is another source (quartzite is metamorphosed sandstone). All combined, world resources of silicon are plentiful and will supply demand for many decades to come. Extraction, Processing and Production Ferrosilicon is extracted from itsminerals and produced by reduction of silica or sand with coke in presence of scrap iron, millscale, or other source of iron. Ferrosilicon with silicon content up to about 15% is made in blast furnaces lined with acid fire bricks. Ferrosilicon with higher silicon content is made in electric arc furnaces. The usual formulations on the market are ferrosilicon with 15%, 45%, 75%, and 90% silicon. Uses and other Properties Ferrosilicon is used as a source of silicon to reduce metals from their oxides and to deoxidize steel and other ferrous alloys. This prevents the loss of carbon from the molten steel. It can Page 6 of 11
  • beused to make other ferroalloys. Ferrosilicon is also used for manufacture of silicon, corrosion-resistant and high-temperature resistant ferrous silicon alloys, and silicon steel for electromotors and transformer cores. In the manufacture of cast iron, ferrosilicon is used for inoculation of the iron to accelerate graphitization. In arc welding, ferrosilicon can be found in some electrode coatings.Ferrosilicon is a basis for manufacture of pre-alloys like magnesium ferrosilicon (FeSiMg), used for modification of melted malleable iron. FeSiMg contains 3–42% magnesium and small amounts of rare earth metals. Ferrosilicon is also important as an additive to cast irons for controlling the initial content of silicon.Ferrosilicon is also used in the Pidgeon process to make magnesium from dolomite Ferromanganese Description Ferromanganese, a ferroalloy with high content of manganese, is made by heating a mixture of the oxides MnO2 and Fe2O3, with carbon, usually as coal and coke, in either a blast furnace or an electric arc furnace-type system, called an immersed curve furnace Mining Manganese which is used to form Ferromanganese is mined in the form of manganese ores which is usually done in open pits. Some ores are upgraded by washing, and undersized ores can be agglomerated by sintering. Several processes have been developed for mining seafloor nodules, but they cannot compete economically with the ready exploitation of high-grade terrestrial deposits. The most important manganese ores are the oxides pyrolusite, romanechite, manganite, and hausmannite and the carbonate ore rhodochrosite. Rhodonite and braunite, both silicate ores, are frequently found with the oxides. Only ores containing greater than 35 percent manganese are considered commercially exploitable. Extraction, Processing and Production High carbon ferromanganese is produced in blast furnaces in a process similarto the production of pig iron in blast furnaces. But there are some importantdifferences between two processes. The iron oxides are reduced by CO in the shaft region of the furnace according to the reactions given below: 3Fe2O3 + CO = 2Fe3O4 + CO2………..(1) Fe3O4 + CO = 3FeO + CO2…………...(2) FeO + CO = Fe + CO2………………...(3) Manganous oxides are reduced by solid carbon in the bosh and heart regionsof blast furnace because of higher temperatures according to reactions given below: Mn3O4+ 4C = 3Mn + 4C …………….(4) MnO + C = Mn + CO ………………...(5) Page 7 of 11
  • Thus, ferromanganese production in blast furnace needs larger amounts ofcoke than pig iron production in a blast furnace. Preheating the blast and oxygenenrichment are used to reduce coke requirement. Dolomite or limestone added to thecharge raises the activity of MnO for reduction. Small slag volume, basic slag andblast temperature are required for high manganese recovery. Low-carbon ferromanganese contains 76 – 92% Mn and 0.5 – 0.75% C. Theproduction of low-carbon silicomanganese is not possible by the decarburization of high carbon ferromanganese without extremely high losses of manganese. It must accordingly be made of a silicothermic reduction process Uses and other Properties There are different types of ferromanganese alloys based on carbon and manganese content. Low-Carbon Ferromanganese has a carbon content ranging from 0.07 to 0.75%. MediumCarbon Ferromanganese contains 80-85 % Mn, 1.25-1.50% C and 1.50% Si (max.).HighCarbon Ferromanganese contains 80-75% Mn, 7.5% C and 1.2% Si. Low-Fe Ferromanganese contains 85-90 % Mn, 2 % Fe, 3 %Si, and 7 % C.The high carbon ferromanganese is used as a de-oxidizer for steel tools. Low Carbon Ferromanganese is important for manufacturing stainless steel, heat resistant steel & electric welding electrodes. Ferromanganese is also used to counteract the harmful effects of sulphur during the production of steel and cast iron. It enhances irons toughness and strength. Ferro Manganese is also used to increase both the total carbon and combined carbon content of the iron. By increasing the total carbon manganese tends to increase graphite and therefore decreases shrinkage. Although it increases the toughness (ductility and strength), at too high a concentration it will unfavourably affect the machinability of cast iron. Ferrovanadium Description Ferro Vanadium is an alloy which is formed by combining iron and vanadium with a vanadium content range of 35%-85%. Ferro Vanadium is a universal hardener, strengthener and anti-corrosive additive for steels like high-strength low-alloy steel, tool steels, as well as other ferrous-based products. Ferro Vanadium was first used in the production of the Ford Model T and is still used in the automobile industry today. Mining Ferrovanadium is formed by the combination of iron and vanadium, so the vanadium or ferrovanadium is extracted from mined vanadium minerals which are are patronite (VS2), carnotite [K2(UO2)2(VO4)2], and vanadinite, [Pb5 (VO4)3Cl]. The world’s largest mines of vanadium are from titaniferous magnetite reserves in such regions as the Bushveld of South Africa. Other sources of vanadium include ash from the combustion of fossil fuel, slag from phosphate ore, the aluminum ore bauxite, and spent catalysts. Page 8 of 11
  • Extraction, Processing and Production Vanadium is extracted from carnotite as a co-product with uranium by leaching the ore concentrate for 24 hours with hot sulphuric acid and an oxidant such as sodium chlorate. After removal of solids, the leachate is fed into a solvent extraction circuit where the uranium is extracted in an organic solvent consisting of 2.5-percent-amine–2.5-percent-isodecanol–95percent-kerosene. Vanadium remains in the raffinate, which is fed into a second solvent extraction circuit. There vanadium in turn is extracted in the organic phase, stripped with a 10 percent soda ash solution, and precipitated with ammonium sulphate. The ammonium metavanadate precipitate is filtered, dried, and calcined to V2O5. Most other vanadiumbearing ores or slags are crushed, ground, screened, and mixed with a sodium salt such as sodium chloride or sodium carbonate. This charge is then roasted at about 850° C to convert the oxides to sodium metavanadate, which can be leached in hot water. With the acidulation of the leachate with sulphuric acid, the vanadium is precipitated as sodium hexvanadate. This compound, known as red cake, can be fused at 700° C to yield technical-grade vanadium pentoxide (at least 86 percent V2 O5, or it can be further purified by dissolving it in an aqueous solution of sodium carbonate. In the latter case, the iron, aluminum, and silicon impurities in the red cake precipitate from solution upon adjustment of the acidity. The vanadium is precipitated as ammonium metavanadate by adding ammonium chloride. After filtration, the precipitate is calcined to produce V2O5 of purity greater than 99.8 percent. Ferrovanadium is also extracted and produced directly by reducing a mixture of vanadium oxide, iron oxides and iron in an electric furnace.The other method of production of FeV is by Aluminothermic reduction process which requires the addition of V2O5, aluminium, lime and iron scrap mixed together and placed in a refractory lined ladle. The ladle is ignited with the reaction being fully autogenous. On completion of the reaction, the FeV has collected at the bottom of the ladle and a high Al2O3 slag forms above the FeV.After cooling, the slag and metal are separated. The FeV is crushed, sized and packed to customer requirements. The slag is crushed, some of the slag recycled back into the process and the balance sold. All fumes generated in the process are collected in a gas cleaning plant and recycled.The other method for the production of Ferrovanadium is by the Direct Current Arc Furnace. Uses and other Properties The largest practical application of Ferro Vanadium is in the alloying process of any hardened steel. That steel is then, in turn, used in gears, axles, crankshafts, bicycle frames and other highly critical steel components. Ferro Vanadium forms stable carbides and nitrides that will result in a significant increase in strength.High-carbon steel alloys (HSS) with a vanadium content range of 1%-5% are used for high-speed tool steels as well as in surgical tools and instruments. Ferro Vanadium also stabilises the beta form of titanium, which in turn increases the temperature stability of titanium. Mixed with aluminium in titanium alloys, Ferro Vanadium is also used in high-speed airframes and jet engines.Ferrovanadium is also used to reduce weight while simultaneously increasing the tensile strength of the material. Page 9 of 11
  • 3. REFERENCING      Hermones, T.D. (2001). Principles of Refinery Processes in Metallurgy. New York: MacMillian. Principles of Extractive Metallurgy.(n.d.). Available From: http://books.google.co.za/books_principles_of_extractive_metallurgy.htm (Accessed 01 October 2012). Properties of Ferroalloys.(n.d.). Available From: http://en.wikipedia.org/wiki/Ferroalloys.htm (Accessed 29 September 2012) Production of Ferroalloys.(n.d.). Available From: www.exxaro.com/content/ops/metals_ferroalloys.asp (Accessed 01 October 2012) Askeland, D.R.(2009). The Science and Engineering of Materials. Missouri: Pearson Page 10 of 11