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 .
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 .
- 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 :
- 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,
- Impure Metal M is used as anode .
- It is connected to the positive terminal of the battery.
- A strip of pure metal M is used as a cathode .
- It is connected to the negative terminal of the battery.
- A solution of metal salt M is used as the electrolyte .
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 .