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Physical Chemistry

Language of Chemistry Stoichiometry Atomic Structure Oxidation and Reduction Periodic Table Acid and Base Electronic Theory of Valency Equivalent Weight and Atomic Weight

Physical Chemistry-II

Non-Metals

Inorganic Chemistry

Introduction Compound of Metals Hydroxide Chlorides And Nitrates Sulphates And Carbonates General Metallurgy Sodium and Its Compounds Copper Zinc Iron

Iron

Introduction:

Symbol: $F e$
Atomic Number: $26$
Iron is the most abundant metal on Earth.
Electronic Configuration of $F e : [A r] 3 d^{6} 4 s^{2}$
Density of iron is $7.874$
Valency: $2 an d 3$
Electronic Configuration of $F e^{2 +} : [A r] 3 d^{6}$
Electronic Configuration of $F e^{3 +} : [A r] 3 d^{5}$
Ores:

-Hematite $(F e_{2} O_{3})$

-Magnetite $(F e_{3} O_{4})$

-Siderite $(F e C O_{3})$

-Limonite $(F e_{2} O_{3} .3 H_{2} O)$

-Iron Pyrite $(F e S_{2})$

Extraction of Cast Iron from Hematite

Crushing and Pulverization:

-Big lumps of ore are crushed with jaw crushes and pulverized with ball mill.

Concentration:

-The ore is then washed with cold water and concentrated by gravity separation or electromagnetic separation.

Calcination or Roasting:

- The Hematite ore is oxide ore, so it is calcinated (i.e. heated in limited supply of air.)

-Moisture is removed.

$2 F e_{2} O_{3} .3 H_{2} O ⟶ △ 2 F e_{2} O_{3} + 6 H_{2} O$

Iron Carbonate present also decomposes to $F e O$ .

$F e C O_{3} ⟶ ∆ F e O + C O_{2}$

-The $F e O$ is obtained from $F e C O_{3}$ and initially present $F e O$ reacts with limited air to for $F e_{2} O_{3}$

$4 F e O + 3 O_{2} ⟶ 2 F e_{2} O_{3}$

-This is very important step because $F e O$ easily combines with $S i O_{2}$ to form slag, which is finally lost. But, $F e_{2} O_{3}$ doesn't react with $S i O_{2}$ and iron loss is saved.

Smelting:

-The calcinated ore is heated on blast furnace with coke and limestone (flux).

-In this smelting process the iron oxide is reduced to metallic form.

-The blast furnace has different zones, which are: ( from bottom to top of blast furnace)

Zone of Combustion:

-It is lowermost zone where coke is brunt to give the highest temperature of furnace up to $150 0^{\circ} C$

$C + O_{2} ⟶ ∆ C O_{2}$

Zone of Fusion

-It is the zone where iron and slag starts fusing. So, temperature decreases to about $130 0^{\circ} C$

$C O_{2} + C ⟶ ∆ 2 CO - (h e a t)$

Zone of Slag Formation

-It is middle portion of furnace where temperature reaches from (800^.C-1000^.C)

- $C a C O_{3}$ is said to be flux and is added externally.

$C a CO 3 ⟶ 10 0^{\circ} C C a O + C O_{2}$

$C a O (f l ux) + S i O_{2} (G an gu e) ⟶ C a S i O_{3}$

Zone of Reduction

-It is uppermost region where ore is reduced to metal $CO$ as reducing agent.

-Temperature is about $(40 0^{\circ} - 70 0^{\circ})$

$F e_{2} O_{3} + 3 CO + ⟶ ∆ 2 F e + 3 C O_{2}$

-Thus obtained iron is called spongy iron.

-The upper zone is called zone of preparatory heating where temperature ranges from $30 0^{\circ} C - 40 0^{\circ} C$ .

-In this zone moisture and other waste gases are removed.

-At the end of smelting, molten slag settles down and floats over molten ion, which absorbs Silicon, Phosphorous, Sulphur, etc.

-The Molten iron thus obtained is called pig iron.

-When pig iron is remelted, it becomes cast iron.

Commercial forms of Iron:

i) Cast or Pig iron:

-Most impure form of iron.

-It has carbon contain of $2.5% - 4.5%$ with small quantities of $S, P, M n an d S i$ .

-It is very hard and has low M.P of $122 7^{\circ} C$ .

ii) Wrought iron:

-Most purest form of iron.

-Contains $0.12% - 0.25%$ carbon in it.

-It has less than $0.25%$ of other impurities like $S, P, S i, M n,$ etc.

-It melts at $153 0^{\circ} C$ and is soft and malleable.

iii) Steel:

-It has carbon content about $0.25% - 2%$ , which traces of sulpher, phosphorous and special constituent like $t u n g s t e n, C r, V,$ etc.

Mild Steel: Has lower $%$ of Carbon.
Hard Steel: Containing large $%$ of Carbon.
Alloy Steel: Valuable properties may be granted to steel adding other such metals such as $N i, C o, C r,$ etc. Eg: Stainless steel $(F e + C r + N i)$