Extraction Of Lithium And Sodium

          The alkali metals are strong reducing agents (high reduction potential values, Table 12.2) and are very reactive. These cannot be extracted by the usual methods due to the following difficulties:

(i)                  Lithium and sodium are very strong reducing agents. Therefore, they cannot be isolated by reduction of their oxides or other compounds.

(ii)                 These metals cannot be extracted by the electrolysis of their aqueous solutions because the metals formed will immediately react with water forming their hydroxides.

(iii)                These metals cannot be prepared from the aqueous solution of their salts by metal displacement method because they react with water violently.

Therefore, these metals are generally isolated by the electrolysis of their fused metal halides.

A.   Extraction of Lithium

The extraction of lithium from its minerals involves the following two steps:

1.   Conversation of lithium into lithium chloride.

2.   Electrolysis of lithium chloride.

Conversation of lithium into lithium chloride. The minerals are first of all conversation into lithium chloride by any one of the following methods:

(i)          The ore is heated to about 1373 K to convert it into the less dense and more friable from. It is then washed with sulphuric acid at 523 K and leached with water to give lithium sulphate monohydrate, Li₂SO₄, H₂O. it is then treated successively with sodium carbonate solution and HCl which gives insoluble lithium carbonate (Li₂CO₃) and finally lithium chloride.

(ii)         The washed ore is calcined with limestone (CaCO₃) at 1273 K and then leached with water to form LiOH. It is then treated with HCl to from LiCl.