Question

Explain the permutit method for softening hard water.

Answer 1

This is a modern method employed for the softening of hard water. hydrated sodium aluminium silicate (Na2Al2Si2O8.xH2O) is called permutit. These complex salts are also known as zeolites.

The process of softening of water is carried in a tall cylindrical vesse packed with coarse sand (or gravel) and permuitit. Hard water is introduced through an inlet. It first reaches the bottom of the vessel. As it rises up, the suspended inpurities are removed by gravel. It then comes in contact with permuitit which exchanges $C{a}^{+2}$ and $M{g}^{+2}$ ions present in tank water with Na+ ions.The water that rises through permuitit layer is free from Ca2+ and Mg2+ ions and is therefore, soft.It can be taken out from outlet.

$N{a}_{2}Z+C{a}^{+2}⟶CaZ+2N{a}^{+}$

Sodium zeolite (From hard water) Cal. Zeolite

$N{a}_{2}Z+M{g}^{+2}⟶MgZ+2N{a}^{+}$

Sodium zeolite (From hard water) Mag. Zeolite

where Z = $A{l}_{2}S{i}_2{O}_8.x{H}_{2}O$

Regeneration of Permuitit: After sometime, the entire $N{a}_{2}Z$ gets converted into CaZ

and MgZ. Then the permuitit will n o longer function. In order to regenerate Na2Z, the entry of hard water is stopped and in its place a 10% NaCl solution is introduced when $C{a}^{+2}$ and $M{g}^{+2}$ ions are exchanged by Na+ ions and permuitit gets regenerated. The $C{a}^{+2}$ and $M{g}^{+2}$ ions are washed away by water and permuitit, thus regenerated and can be used again for softening of hard water