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Wednesday, 12 December 2012

Extraction of Iron From Iron Ore : Produce more Iron to Fulfill The Need of Iron During The Modern Iron Age.

Blast furnace in Sestao, Spain. The furnace itself is inside the central girderwork.

Extraction Of Iron From Iron Ore:

Detail Drawing of Blast Furnace with all its Major Parts with Number

Description of Blast furnace  :
1: Iron ore
2: Calcareous sinter, iron oxide pellets,
3: Calcium Carbonate (lime stone) CaCO3
4: a valve that prevents direct contact with the internal parts of the furnace and outdoor air
5: Layers of cokes, sinter, iron oxide pellets, ore, (3)
6: Layers of cokes, sinter, iron oxide pellets, ore, (3)
7: Hot air (around 1200°C)
8: Slag
9: Liquid pig iron
10: Mixers
11: Tap for pig iron
12: Dust cyclon for removing dust from exhaust gasses before burning them in 13.
13: air heater
14: Smoke outlet (can be redirected to carbon capture & storage (CCS) tank)
15: feed air for Cowper air heaters
16: Powdered coal
17 cokes oven
18 cokes 

3D Blast Furnace diagram

3D Blast Furnace diagram
1. Hot blast from Cowper stoves
2. Melting zone
3. Reduction zone of ferrous oxide
4. Reduction zone of ferric oxide
5. Pre-heating zone
6. Feed of ore, limestone and coke
7. Exhaust gases
8. Column of ore, coke and limestone
9. Removal of slag
10. Tapping of molten pig iron
11. Collection of waste gases

Different Parts of Furnace

Iron occurs in the free state as meteorites which also contain 20 to 30 % nickel. In the combined state, iron occurs in the following minerals.

   Magnetite, Fe3O4    

Hematite, Fe2O3

Spathic iron ore, FeCO3

   Iron Pyrites , FeS2 

        Magnetite, Fe3O4                                                          Hematite, Fe2O3
        Limonite,3 Fe2O3.H2O                                                 Spathic iron ore, FeCO3
        Iron Pyrites , FeS2                                                       Copper pyrites, CuFeS2

Tin occur scarely in the free state but in the form of compounds it exists in a large number of minerals , e.g. pyrites ore of copper, iron and zinc.The most important source of tin is cassiterite or tin stone, SnO2. Both iron and tin are extracted by the carbon reduction method.

The main chemical reaction producing the molten iron is:

Fe2O3 + 3CO → 2Fe + 3CO2

Preheated blast air blown into the furnace reacts with the carbon in the form of coke to produce Carbon monoxide and heat. The carbon monoxide then reacts with thei ron oxide to produce molten iron and Carbon dioxide . Hot carbon dioxide, unreacted carbon monoxide, and nitrogen from the air pass up through the furnace as fresh feed material travels down into the reaction zone. As the material travels downward, the counter-current gases both preheat the feed charge, decompose the limestone to Calcium oxide and carbon dioxide, and begin to reduce the iron oxides in the solid state. The main reaction controlling the gas atmosphere in the furnace is called the  Boudouard reaction:

C + O2 → CO2
CO2 + C → 2CO 

The decomposition of limestone in the middle zones of the furnace proceeds according to the following reaction:

CaCO3 → CaO + CO2 

The calcium oxide formed by decomposition reacts with various acidic impurities in the iron (notably silica), to form a fayalitic slag which is essentially calcium silicate, 

SiO2 + CaO → CaSiO3 

In reduction zone (675 k - 975 k) where iron oxide is reduced to spongy iron by crbon monoxide rising up the furnace

Fe2O3 + 3CO -----> 2Fe + 3CO2

This reaction is believed to take place in stages:

3Fe2O3 + 3CO -----> 2Fe3O4 + CO2
Fe2O3 + CO -----> 3FeO + CO2
FeO + CO ----> Fe + CO2

The "Pig Iron" produced by the blast furnace has a relatively high carbon content of around 4-5%, making it very brittle, and of limited immediate commercial use. Some pig iron is used to make cast iron. The majority of pig iron produced by blast furnaces undergoes further processing to reduce the carbon content and produce various grades of steel used for tools and construction materials.

Although the efficiency of blast furnaces is constantly evolving, the chemical process inside the blast furnace remains the same. According to the "American iron and still institute "Blast furnaces will survive into the next millennium because the larger, efficient furnaces can produce hot metal at costs competitive with other iron making technologies." One of the biggest drawbacks of the blast furnaces is the inevitable carbon dioxide production as iron is reduced from iron oxides by carbon and there is no economical substitute - steelmaking is one of the unavoidable industrial contributors of the CO2 emissions in the world The challenge set by the greenhouse gas emissions of the blast furnace is being addressed in an on-going European Program called ULCOS( Ultra low CO2Stillmaking )Several new process routes have been proposed and investigated in depth to cut specifc emissions (CO2 per ton of steel) by at least 50%. Some rely on the capture and further storage (CCS) of CO2, while others choose decarbonizing iron and steel production, by turning to hydrogen, electricity and biomass  In the nearer term, a technology that incorporates CCS into the blast furnace process itself and is called the Top-Gas Recyling Blast Furnace is under development, with a scale-up to a commercial size blast furnace under way. The technology should be fully demonstrated by the end of the 2010s, in line with the timeline set, for example, by the EU to cut emissions significantly. Broad deployment could take place from 2020 on.

Extraction of Tin

Tin Stone SnO2

Tin Stone SnO2

Metallic tin is extracted from tin stone which contains about 10% of metal as SnO2, the rest being siliceous matter, tungstates of Fe, Cu and As. After crushing , the ore is concentrated by washing in a current of water (Gravity process to remove lighter gangue particles) and by magnetic separator to remove tungstates of Fe and Mn . The ore is rotated to remove sulphate of Cu and Fe.Finally the ore is smelted in a reverberatory furnace or in a blast furnace at 1475 ---- 1575 K. The ore is mixed with 1/5 th of its mass of powered anthracite and little of lime or fluorspar which is used as flux.Tin oxide is reduced to tin:

        SnO2 + 2C ----> Sn + 2CO

 The molten metal collected from the bottom of the furnace contains impurities such as Fe, Pb, S and As.The metal may be purified electrolytically.

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