Extraction of Metal from Ore

• It is the process of extracting metal from its concentrated ore . It is the next step after concentration of ore.
• The extraction method depends upon the reactivity series of metals .

Extraction of Less Reactive metals in the Reactivity Series

Metals low in the reactivity series are very unreactive . The oxides of these metals can be reduced to metals by heating alone.

These include Metals like Mercury and Copper . 

1. Mercury Sulphide (HgS) or Cinnabar is the ore of mercury
   Mercury can be directly extracted from its sulphide ore by heating it in air.
   The process involves two steps:
   Conc. Mercury (II) Sulphide ore, Cinnabar, is roasted in air.

Mercury Oxide is formed .

The oxide is heated to about 300℃.

It gets reduced to form Mercury metal.

(II) Extraction of Copper

Conc. Sulphide ore Cu ₂ S is roasted in air to form Copper Oxide.

When enough Cu ₂ S has been converted to Cu ₂ O, the supply of air is cut.

Cu ₂ O reacts with the remaining Cu ₂ Sto form Cu.

Extraction of moderately reactive metals :

In order to be extracted, these are reduced from their oxides , with reducing agents like carbon, aluminium, sodium or calcium.

• It is easier to obtain metals from their oxides than from carbonates or sulphides.
• Thus, the concentrated ores are converted into metal oxide by the process of calcination or roasting .
• A carbonate ore is converted into oxide by calcination whereas a sulphide ore is converted by roasting .

1. CALCINATION :

• The carbonate ore is heated strongly in the absence of air to convert it into metal oxide.
• Example - Calamine ore, ZnCO ₃  

In order to extract zinc metal from this ore, it must first be converted into zinc oxide from zinc carbonate. This is done by Calcination.

The reaction is as follows :

1. ROASTING :

• The sulphide ore is strongly heated in the presence of air to convert it into metal oxide. 
• Example - Zinc occurs as a sulphide ore, ZnS . 

This sulphide is first converted to oxide by the process of roasting and then the zinc metal is extracted from it. 

The reaction is as follows  :

Extraction of Reactive Metals 

• The highly reactive metals like Potassium, Sodium, Calcium, magnesium and aluminium do not have stable oxides.
• These cannot be reduced by carbon (reducing agent).

These metals are extracted by the electrolytic reduction of their molten chlorides or oxides . 

In electrolytic refining,

1. Impure Metal M is used as anode . 

• It is connected to the positive terminal of the battery.

2. A strip of pure metal M is used as a cathode . 

• It is connected to the negative terminal of the battery.

3. A solution of metal salt M is used as the electrolyte .

For example 

NaCl → Na + (l) + Cl – (l)

• During electrolysis , the negatively charged electrode ( cathode ) acts as a powerful reducing agent .
• It supplies electrons to reduce the metal ions into metal . 
• This is because metals being positively charged ions are attracted towards the negatively charged cathode. 

At cathode: reduction of 2Na + (l) + e – → Na(l)

• The anode provides a strong positive charge to attract the anions .
• It oxidises the anions to form Chloride gas/Oxygen .

At anode: oxidation of 2Cl – (l) → Cl ₂ (g) + 2e –

Net Reaction is written as: 2Na + (l) + 2Cl – (l) → 2Na(l) + Cl ₂ (g)

Example : Sodium , Potassium , Calcium and Magnesium are extracted by electrolysis of their molten chlorides whereas Aluminium metal is extracted by electrolysis of its molten oxide .