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Extraction of iron from its ore is said to be the third and the last process in metallurgy. Iron oxides are the most prevalent ores. By burning these oxides with carbon in the form of coke, they may be converted to iron.The process of making coke involves heating coal in the absence of oxygen. Hematite Fe2O3, and magnetite are the most widely utilized iron ores. Three important processes follow the extraction of iron and separation of the metals: Concentration of Ore, Extraction of Iron from its concentrated ore, Purification of Iron.
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Key Terms: Ore, Coke, Blast Furnace, Iron Extraction, Calcination, Roasting, Malleable
Concentration of Ore
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The method of extracting iron begins with concentration by calcination, which is a thermal breakdown process in which a restricted amount of oxygen is supplied to ores. An impure source is a metal's ore. It contains a variety of contaminants besides metals. These impurities are referred to as gangue, and because they are commercially worthless, we must extract them from the ore. The concentration of ores is the name for this procedure. Water and other impurities such as sulfur and carbonates are removed during the concentration process.
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Extraction of Iron from its Concentrated Ore
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The ore of iron is mixed with limestone and coke before putting it into the blast furnace. The extraction of iron occurs in the blast furnace.
- The term "blast" refers to the supply of combustion air above atmospheric pressure. The concentrated ore is reduced to a liquid chemical condition in the blast furnace.
- The concentrated iron ore, coke, and limestone are supplied from the top and a blast of hot air is forced into the bottom of a blast furnace, which is used to smelt industrial metals. All of these materials are crushed into small bits and mixed before being placed in a hopper that controls the input.
- Coke is burned at temperatures of roughly 2200K in hot air blasted from the bottom. The majority of the heat required for this process comes from burning coke.
- At such high temperatures, coke reacts with oxygen in the heated air to produce carbon monoxide (CO). CO and heat are now increasing, colliding with the raw material dropping from the top.
- The temperature in the upper parts of the Blast Furnace is substantially lower than the lower areas, which are 2200K. Haematite (Fe2O3) and Magnetite (Fe3O4) are converted to Ferrous Oxide in this section (FeO).
Below are the reactions in the blast furnace at lower temperatures (500K-800K):
Fe2O3 + CO → 2Fe3O4 + CO2
Fe3O4 + 4CO→ 3Fe + 4CO2
Fe2O3 + CO → 2FeO + CO2
In the lowest sections of the furnace, at 900-1500 K,
C + CO2 → 2CO
3FeO + CO2 → Fe + CO2
Calcination
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Calcination is the process of turning ore into an oxide by exposing it to high temperatures. Ore is heated below its melting point in the absence of air or with a regulated supply of air. This procedure converts carbonates and hydroxides into their corresponding oxides.
Calcination is a thermal process that is used to transform ores and other solid materials into liquids by providing a thermal breakdown. The procedure of calcination is used to decompose limestone (calcium carbonate) into lime (calcium oxide) and carbon dioxide. Calcines are the byproducts of the calcination process.
CaCO3 → CaO + CO2
Roasting
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Roasting is a metallurgical technique. It heats an ore over its melting point in the presence of extra air, converting it to its oxide. While roasting is commonly used to convert sulfide ores, calcination is most commonly employed to oxidize carbonates. During the roasting process, moisture and non-metallic impurities in the volatile gasses are removed.
The technique has a major disadvantage in that it includes sulfides, which are a major source of air pollution. Aside from that, the process of releasing a vast number of metallic, poisonous, and acidic substances causes environmental damage. Roasting is seen when zinc sulfide is transformed into zinc oxide.
2ZnS + 3O2 → 2ZnO + CO2
Purification of Iron
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The limestone subsequently decomposes to produce CaO, which eliminates impurities from the ore in the form of slag. The molten iron may then be readily separated from it. Blast Furnaces produce iron with a carbon content of 3–4% and minor amounts of other impurities including sulfur, silicon, and other metals. This is known as Pig Iron. It is a hard but brittle metal whose strength is hampered by impurities. Pig iron is melted again using scraps of iron and coke and exposed to a blast of hot air to minimize the carbon content. Cast iron is a kind of iron with a lower carbon concentration of roughly 2–3%.
Purification of Iron
Reactions involved in the purification of metals:
CaCO3 → CaO + CO2
The calcium oxide then reacts with the hematite's silica impurities to form slag.
CaO(s)+ SiO3(s) → CaSiO3(l)
Malleable Iron
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Malleable Iron is the finest type of iron accessible commercially, and it's made from cast iron heated in a Haematite-lined furnace (Fe2O3). After that, the haematite combines with the carbon in the cast iron, producing pure iron and carbon monoxide gas.
Fe2O3 + 3C → 2Fe + 3CO
The slag is then made from limestone. Impurities like S and Si enter the slag, which may then be readily separated to give pure iron. Hematite, magnetite, limonite, and siderite are the iron minerals utilized as ores. The most significant iron ore is hematite.
Extraction of Iron from its Oxides
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Oxide ores of iron are combined with limestone and coke and fed into a blast furnace from the top after being concentrated by calcination or roasting. Here, the oxide is converted to metal. When molten pig iron is cooled quickly, it is known as white cast iron, and it includes carbon in the form of Fe3C(cementite), but when it is chilled slowly, it is known as grey cast iron, and it contains carbon in the form of graphite.
Things to Remember
- Slag is a calcium silicate compound.
- The majority of the molten iron produced by a blast furnace is utilized to create various forms of steel.
- Calcination is the process of turning ore into an oxide by exposing it to high temperatures.
- Hematite is the most significant iron ore.
- Calcination is the first phase in the iron extraction process, which is followed by a few significant processes.
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Sample Questions
Ques. What is metallurgy? (2 marks)
Ans. Metallurgy refers to the entire scientific and technological process of isolating metal from its ores. Because it is a part of our daily life, metallurgy is a very significant and popular activity. One of the most common instances of metallurgy is iron extraction in a blast furnace.
Ques. Explain Wrought Iron. (4 marks)
Ans. Wrought iron is the purest type of iron that can be purchased. Wrought iron is made by heating cast iron in a furnace coated with haematite Fe2O3. Carbon is reacted with Haematite to produce pure iron, and carbon monoxide gas is released in the process. This can be written as:
Fe2O3 + 3C → 2Fe + 3CO
The next stage is to add limestone as a flux to make slag, at which point impurities such as S and Si pass through to the slag. Later, the slag is removed to obtain pure iron. The procedure outlined above explains how to extract iron from a blast furnace. One of the most essential processes in the study of metallurgy is the melting of metals.
Ques. What is the main impurity in iron extraction? (2 marks)
Ans. Carbon, sulphur, phosphorus, and silicon are all impurities found in Blast Furnace iron. These must be eliminated. Sulphur must first be eliminated through a separate procedure. Magnesium powder is blown into molten iron, where it combines with sulphur to generate magnesium sulphide.
Ques. How do you extract iron from the ground? (2 marks)
Ans. The iron is extracted from the ground by Smelting. Raw ore is a combination of elements termed ore proper and loose soil called gangue that is mined out of the ground (waste). Crushing the raw ore separates the ore proper from the lighter dirt, which is then washed away. It's more difficult to separate the ore from its contaminants.
Ques. What are the current methods of iron extraction? (3 marks)
Ans. Three important processes follow the extraction of iron and separation of the metals: Concentration of Ore, Extraction of Iron from its concentrated ore, Purification of Iron. It's a long process that starts with calcination, roasting and concentration. Water and other volatile contaminants such as sulphur and carbonates are removed during concentration. This concentrated ore is put into the blast furnace with limestone (CaCO3) and Coke from the top.
Ques. How is carbon removed from molten iron? (2 marks)
Ans. Carbon is removed by mixing impure molten iron with scrap iron (from recycling) and blowing oxygen into the mixture. The oxygen interacts with the impurities left behind to generate a variety of oxides. Carbon monoxide is formed when carbon is burned. Because this is a gas, it separates from the iron!
Ques. How is limestone used in iron extraction? (2 marks)
Ans. The primary function of limestone in iron extraction is to disintegrate in a hot furnace and produce calcium oxide. In a blast furnace, iron is produced from its mineral, haematite. The ore, together with coke and limestone, is fed into the top of the furnace. Calcium oxide is formed as the limestone decomposes in the hot furnace.
Ques. What are the types of iron ore? Which slag is formed during the extraction of iron? (4 marks)
Ans. Metallic iron may be recovered from iron ores, which are rocks and minerals. Massive hematite, the most often mined iron ore, magnetite, titanomagnetite, and pisolitic ironstone are the four primary kinds of iron ore deposits. The colors of these ores range from dark grey to brilliant yellow to deep purple to rusty red.
Ferrous slag is produced during the smelting of iron, however, it is dominated by calcium and silicon compositions. Ferrous slag may be broken down into blast furnace slag (made from molten iron's iron oxides) and then steel slag using this method (forms when steel scrap and molten iron combined).
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