Explain calcination, magnetic separation in extraction of metals.

Explanation

Magnetic separation : When the ore but not the gangue particles are attracted by a magnet or vice versa, then the ore can be concentrated magnetically. The machinery used for this purpose is called a magnetic separator. It consists of a leather or a brass belt moving over two rollers, one of which has an electro-magnet in it. When the pulvurised ore is passed over a magnetic pulley, magnetic particles are retained over the belt as long as these particles remain in the field of influence of the magnet, while the non magnetic particles fall off away from the magnetic roller as shown in Fig.

For example, wolframite, `FeWO_(4)` (an impurity) is separated from cassiterite, `SnO_(2)` (ore) by magnetic separation. In this case the impurity is magnetic while the ore is not. The ores containing iron pyrites `(FeS_(2))` are also concentrated by this method. Before, effecting the separation, the ore is roasted for a short time, this converts iron pyrites into magnetic oxide of iron, `Fe_(3)O_(A)`.