Extraction of Tin
Atomic Number: 50
Electronic configuration: [Kr]4d105s25p2)
Tin is extracted from cassiterite ore. The extraction involves the following steps:
- Concentration: The crushed and powdered ore is washed with running water, which removes lighter siliceous matter. Wolframite is removed by electromagnetic separator.
- Roasting: S and As are removed as their volatile oxides. Iron and copper pyrites are converted into their oxides and sulphates
- Washing: This ore is then washed with hot water to dissolve out copper sulphate and iron sulphate. The lighter ferric oxide is washed off while the concentrated tin stone sinks to the bottom. It is called black tin.
- Smelting: Black tin is mixed with carbon and smelted in a reverberatory furnace. The ore is reduced to the metallic state while SiO2 is removed as slag.
SnO2 + 2C Sn + 2CO
CaCO3 CaO + CO2
CaO + SiO2 CaSiO3 (Slag)
Molten metal is cast into ingots or blocks. It is known as block tin and contains about 99.5% of metallic tin.
The metal is purified by:
- Liquation: The easily fusible tin melts away and less fusible impurities (Fe, W, S, As) are left behind.
- Electrolytic refining: In this method, impure tin is made anode and a thin sheet of pure tin is made the cathode. Electrolyte consist of H2SiF6, tin sulphate and sulphuric acid. On passing current, tin is dissolved from anode and gets deposited on the cathode.