REFINING OF METALS
- The metals produced by various reduction processes are not very pure.
- They contain impurities, which must be removed to obtain pure metals.
- The most widely used method for refining impure metals is electrolytic refining -the process of removal of impurities to get pure metal using electricity is known as electrolytic refining
- In this process, the impure metal is made the anode and a thin strip of pure metal is made the cathode.
- A solution of the metal salt is used as an electrolyte.
- On passing the current through the electrolyte, the pure metal from the anode dissolves into the electrolyte.
- An equivalent amount of pure metal from the electrolyte is deposited on the cathode.
- The soluble impurities go into the solution, whereas,
- the insoluble impurities settle down at the bottom of the anode and are known as anode mud.
- The surface of some metals, such as iron, is corroded when they are exposed to moist air for a long period of time.
- This phenomenon is known as corrosion.
PREVENTION FROM CORROSION
- Oil or grease
- Plastic coating
- Tin plating – cover metal by molten tin
- chrome plating
- anodizing – protect metal by formation of thick metal oxide coating of generally aluminium
- making alloys
- Galvanization – cover metal by molten zinc
- Galvanization is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.
- The galvanized article is protected against rusting even if the zinc coating is broken.