132.

Give a brief account of the following processes as used in extraction of metals:
(a) Smelting
(b) Magnetic separation

a) Smelting is a process in which the oxide of metal is reduced to the metal and the metal is obtained in a molten form. In smelting reduction is done at high temperatures.

Two different ways are used to employ smelting;

1: carbon reduction process: Oxide of matter obtained from nature or by calcination or roasting is reduced by a coke through smelting.

MO +C  -->M + CO

During smelting the impurities are also removed. This is done by the addition of a suitable external substance known as flux. Flux reacts with impurities and forms slag which floats over the molten metal and removed.

2: using reduction agent other than carbon: They are many oxides ores which cannot be reduced by carbon. Therefore the powerful reducing agent like aluminum, sodium or magnesium are required. For example, oxides of chromium and manganese etc., are to reduce with aluminum;

Cr₂O₃ + 2Al  --> 2Cr + Al₂O₃

3MnO₂ +4Al  --> 3Mn + 2Al₂O₃

b) Magnetic separation : This method is used when either ores or gangues have strong ferromagnetic nature. Strong ferromagnetic ores e.g. iron, tin or ferromagnetic impurities are thrown in between magnetic poles which attracts ores on poles. E.g. wolframite(FeWO₄) a magnetic ore is separated from the non-magnetic ore.