(1) Purification of impure copper : Impure copper is remelted in a reverberatory furnace lined with SiO2 and a blast of O2 is blows into the furnace. O2 oxidises S, Sb and As to their respective oxides which, being, volatile, get volatilised and are thus removed. Fe is oxidised to FeO which forms a slag of FeSiO3
with SiO2 lining of the furnace. Molten copper left behind contains CuO as impurity. This molten copper is treated with powdered anthracite and then stirred with a pole of green wood. Green wood, at high temperature, liberates hydrocarbon gases, which are converted into methane (CH4). Methane thus obtained reduces CuO to free Cu–metal, which is about 99.5% pure and is called tough pitch copper.
Green wood--> Hydrocarbons--> CH4
4CuO + CH4 --> 4Cu (pure metal) + CO2 + 2H2O
(2) Purification of impure tin : Impure tin metal contains the impurities of Cu, Fe, W and
SnO2. The impurity of SnO2 is due to the incomplete reduction of tin stone ore (SnO2) during smelting. In order to remove these impurities, the impure molten tin metal is taken in a big pot and stirred with a pole of green wood.
Green wood, at high temperature liberates hydrocarbon gases, which are converted into methane CH4. Methane thus obtained reduces SnO2 to pure metal while the impurities of Cu, Fe, W etc. come up to the surface, where they come in contact with air and are oxidised to their respective oxides.
The oxides form a scum on the surface of pure tin metal. This scum is removed from the surface. Tin metal obtained by this method is 99% pure.
Green wood --> Hydrocarbon-->CH4
2SnO2 + CH4 --> 2Sn + CO2 + 2H2O
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