NEET Chemistry Notes General Principles and Processes of Isolation of Metals -Extraction of Crude Metal from Concentrated Ore
Extraction of Crude Metal from Concentrated Ore
Extraction of Crude Metal from Concentrated Ore
It involves two major steps conversion of concentrated ore to oxide, and reduction of the oxide to metal.
Conversion of Concentrated Ore to Oxide
The following steps are considered under the conversion of concentrated ore to oxide.
Calcination
Strong heating of ore in absence of air.
Usually carbonates and hydroxides are converted into oxides by this method.
Volatile impurities of S, As and P are removed as their volatile oxides.
Roasting
Strong heating of ore in presence of air.
The sulphide ores of copper are heated in reverberatory furnace. If the ore contains iron, it is mixed with silica before heating. Iron oxide slags off as iron silicate and copper is produced in the form of copper matte which contains Cu2S and FeS.
SO2 produced is utilised for manufacturing H2S04. Usually sulphide ores are converted into oxides by this method.
In chloridising roasting, the ore containing As, S or Sb as impurity is heated with common salt in presence of silver ores.
In sulphating roasting, sulphide ores are oxidised into sulphate, e.g. ZnS is oxidised to ZnS04.
Reduction of Oxide to Metal
- Reduction of the metal oxide to metal takes place when heated with reducing agents such as C (coke,) or CO or even another metal.
The process is known as smelting.
- Some metal oxides get reduced easily while others are very difficult to be reduced.
- Some metals like Fe dissolve the reducing agent used (carbon) in their extraction. This can be removed by heating the impure metal with more of the ore.
- Misch metal is used as a reducing agent for extraction of pure vanadium. Hydrogen is used as a reducing agent in extraction of pure tungsten and vanadium.
Refining
The metal obtained from the above processes is not 100% pure, hence called crude metal. From the impure metal, the metal of high purity is obtained by refining. Several techniques are used in refining depending upon the differences in properties of the metal.
- Distillation
This process is very useful for low boiling metals like zinc, cadmium and mercury. The impure metal is evaporated to obtain the pure metal as distillate. - Liquation
In this method, low melting metals like tin, bismuth and lead can be made to flow on a sloping surface of a reverberatory furnance and heated above their melting point. In this way it is separated from higher melting impurities. - Electrolytic Refining
Copper is refined by using an electrolytic method.
- Zone Refining
This method is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal. This method is very useful for producing semiconductors and other metals of very high purity, e.g. germanium, silicon, boron, gallium and indium. - Vapour Phase Refining
In this method, the metal is converted – into its volatile compound. It is then decomposed to give pure metal.
Chromatographic method This method is based on the
principle that different components of a mixture are adsorbed differently on an adsorbent.