Metals & Metallurgy Formulas

The important and standard formulas of the Metals & Metallurgy concept are listed here by keeping the student's level of understanding & knowledge. Right from the introduction to properties of metals concepts formulas are explained & given here in the form of list & tables. You can make the most out of this Metals & Metallurgy Formula Tables and improve your subject knowledge and make your calculations done easily & quickly.

INTRODUCTION:
The process of extraction of metal from its ores in profitable manner.

• Mineral is a substance in which metal is present in either native state or combined state.
• ‘‘Ore” is the mineral from which the metal can be economically and conveniently extracted.
• “Gangue or matrix” is the non metallic impurities present in the ore.

IMPORTANT ORES

Process of metallurgy involves –

• Concentration
• Isolation
• Purification

1. Concentration:

• Magnetic separation for ores of iron.
• Froath floatation for sulphide ores.
• Leaching (hydromatallurgy): Bayer’s process for A1 & cyanide process for Au and Ag.

2. Isolation:
(i) Calcination:
(Conversion of the concentrated ore into its oxide form):

• Ore is heated in absence of air to remove water or CO₂ from hydrated oxides or carbonates respectively
• Process temperature is below the melting points of treated ores
• During calcination moisture, volatile impurities are removed there by ore becomes porous

Ex. 2Fe₂O₃.3H₂O → 2Fe₂O₃ + 3H₂O
CaCO₃ → CaO + CO₂

(ii) Roasting (Conversion of the concentrated ore into its oxide form): Employed for sulphide ores

• Ore is heated strongly with other substances, usually with oxygen
• Process temperature is below the melting points of treated ore
• Some of the impurities removed as volatile substances
  S + O₂ → SO₂↑

a. Reduction by carbon (smelting)
The oxides of less electropositive metals like Pb, Zn, Fe, Sn, Cu etc. are reduced by strongly heating with coal or coke. Reduction of the oxide with carbon at high temperature is known as smelting.

b. Reduction by aluminium (Alumino-Thermic reduction)

• Aluminium acts as reducing agent due to its high electropositive nature.
• Oxides such as Cr₂O₃, Mn₃O₄ are reduced by this method because carbon or CO are not efficiently reduced.
• The process is also known as “Gold Schmidt thermite process”.

c. Reduction by heating in air (Auto-reduction)

d. Electrolytic reduction (Electro-metallurgy)
(i) Employed for highly electropositive metals such as Na, K, Ca, Mg, A1 etc.

(ii) These metals are extracted by the electrolysis of their oxides, hydroxides or chlorides in fused state
on fusion: NaCl ⇌ Na⁺ + Cl^– (ions become mobile)
on electrolysis:
at cathode: Na⁺ + e^– → Na
at anode: Cl^– → Cl + e^–
Cl + Cl → Cl₂

e. Hydrometallurgy (Reduction by precipitation)
Process in which more electropositive metals displace less electropositive metals from salt solution. Silver sulphide dissolved in sodium cyanide which forms a soluble complex, then silver is precipitated by the addition of zinc powder.
Ag₂S + 4 NaCN → 2 Na [Ag (CN)₂] + Na₂S(sodium dicyanoargentate (I))
2 Na [Ag (CN)₂] + Zn → Na₂ [Zn (CN)₄] + 2 Ag ↓

3. Refining or purification:

• The metals after reduction process consists of number of impurities like Si, P, slag, oxides, other metals etc.
• Removal of all these impurities to get pure metal is called as refining.

1. Liquation:

• This is based on the principle of difference in melting points of metal and impurity
• Employed for purification of low melting point metals like Pb, Sn etc.

2. Distillation process:

• This is based on difference in boiling points of metals and impurities.
• Employed for low boiling point metals like Zn, Hg etc.

3. Oxidation process

• The impurities converted into oxide & skimmed off from the metal.
• Various oxidation processes used for different metals bear different names, e.g., poling, pudding, bessemerisation and cupellation (for Ag).

4. Electrorefining:
Employed for refining of highly electro positive metals like Al, Cu, Ag, Zn, Sn, Pb, Cr and Ni.
Electrolytic refining of copper:

5. Van-Arkel process:

• In this method, the metal is converted into a volatile unstable compound (e.g. iodide), and impurities are not affected during compound formation.
• Employed for purification of metals like titanium and zirconium.

6. Zone refining:

• Employed for metals which requires in very high purity like semi conductors, such as Si, Ge
• The method is based on the principle that an impure metal on solidification will deposit crystals of pure metal and the impurities will remain behind in the molten part of the metal

7. Mond’s process:
Nickel is purified by using CO gas. This involves the formation of nickel tetracarbonyl.

IRON:
(a) Ores:
Haematite – Fe₂O₃ (chief); Limonite – 2Fe₂O₃.3H₂O ; Siderite – FeCO₃;
Magnetite – Fe₃O₄, Pyrite – FeS₂.

(b) Process:

(c) Reactions:
(i) Roasting: FeO changes to Fe₂O₃ to prevent the loss of iron during smelting.
4FeO + O₂ → 2Fe₂O₃

(ii) Smelting: In reduction zone:
At 400° C
3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂↑
Fe₃O₄ + CO → 3FeO + CO₂ ↑

At 600°C
FeO + CO → Fe + CO₂↑
Ca CO₃ → CaO + CO₂↑

In central zone:
Fe + 2CO → CO₂ + C + Fe
(900 – 1200°C) Fe acts as catalyst here and ‘C’ so formed is dissolved in Fe.
CaO (flux) + SiO₂(impurity) → CaSiO₃(slag)

In fusion zone:
CO₂ + C → 2CO, ΔH = + ve
(1100- 1200°C) melting of iron takes place

In combustion zone:
C + O₂ → 2CO, ΔH = – ve
(1500- 1600°C)

(d) Pig Iron: C 3.1 – 4.5%, small amounts of Si, S, P ; hard and brittle, obtained from blast furnace

(e) Wrought Iron: C 0.15 – 0.28%, purest form ; malleable, fibrous

(f) Steel: C 0.15 – 1.5%, strength is high.

COPPER:
(a) Ores:
Copper pyrites CuFeS₂ (chief) ; cuprite or ruby copper Cu₂O ; copper glance Cu₂S; malachite Cu (OH)₂ . CuCO₃ ; Azurite Cu (OH)₂ . 2CuCO₃.

(b) Process:

(c) Reactions:
(i) Roasting:
2CuFeS₂ + O₂ → Cu₂S + 2FeS + SO₂
2FeS + 3O₂ → 2FeO + 2SO₂
2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂

(ii) Smelling:
Cu₂O + FeS → Cu₂S + FeO
FeO + SiO₂ → FeSiO₃

(iii) Bessemerisation :
2FeS + 3O₂ → 2FeO + 2SO₂
FeO + SiO₂ → FeSiO₃
2Cu₂S + 3O₂ → 2CuO + 2SO₂
Cu₂S + 2Cu₂O → 6Cu²⁺ + SO₂ (self reduction)

(iv) Poling: Molten Cu is stirred with poles of green wood to reduce any copper oxide in Cu.

(v) Electrolytic refining: Anode-impure Cu; cathode – pure Cu; electrolyte CuSO₄ + H₂SO₄.

ALUMINIUM:
(a) Ores:

• Oxides : Bauxite Al₂O₃.2H₂O(chief) ; Diaspore Al₂O₃.H₂O ; corundum Al₂O₃.
• Fluorides : Cryolite Na₃AlF₆.

(b) Process:
(i) Purification of Bauxite:
Baeyer’s Method:
If Fe₂O₃ is major impuirity – Red bauxite
– ore is roasted to convert ferrous oxide to ferric oxide

– NaAlO₂ + 2H₂O → NaOH + Al(OH)₃
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(ii) Electrolysis of fused Alumina.
Cathode : Iron-tank lined with carbon bricks carbon rods
Anode : carbon rods
Electrolyte : Molten [Al₂O₃ (5%) Na₃AlF₆ (85%) + CaF₂(5%) + AlF₃(5%)] O₂ is liberated at anode and A1 collects at the bottom.

(iii) Reactions : Na₃AlF₆ → 3NaF + AlF₃
AlF₃ ⇌ Al³⁺ + 3F^–
At anode : Al₂O₃ + 6F^– → 2Al F₃ + 3/2 O₂ + 6e^–
At cathode : 2Al³⁺ + 6e^– → 2Al

(iv) Electrolytic refining (Floope’s process), three layers process.
Cathode : Carbon electrodes
Anode : Fe tank lined with
Bottom layer : Impure aluminium consists of Cu, Si etc in molten state.
Middle layer : molten mixture of Fluorides of Na, Ba, Al and Al₂O₃
Top layer : pure molten aluminium.
On passing the current, Al is deposited at cathode from the middle layer and an equivalent amount of Al from the bottom layer moves into the middle layer leaving behind the impurities.

SILVER:
(a) Ores : Silver glance or argentite Ag₂S, Ruby silver Ag₂S. Sb₂ S₃, Horn silver AgCl.

(b) Process : Cyanidation or Mac-Arthur-Forrest process

Reactions :

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