Describe about ion exchange method of softening water (or) Explain Zeolite (or) Permutit process.

Explanation

(i) Hardness can be removed by passing through an ion-exchange bed like zeolites or resin containing column. Thus, the zeolites work as water softener.
(ii) Zeolites are hydrated sodium alumino-silicates with a general formula, `NaO.AI_(3)O_(3).xSiO_(2^(3))H_(2)O` (x = 2-10, y = 2-6). They have high ion exchange capacity
(iii) The complex structure can represented as `Na_(2)`-Z with sodium as exchangeable cations This method is called zeolite or permutit process.
(iv) Zeolites have porous structure in which the monovalent sodium ions are loosely held and can be exchanged with hardness producing divalent metal ions (Ca or Mg) in water.
`Na_(2)-Z_((s))+M_((aq))^(2+)M-Z_(s)+2Na_((aq))^(+)`
(v) When exhausted, the materials can be regenerated by treating with aqueous sodium chloride. Hard minerals caught in the zeolite are released and they get replenished with sodium ions.`M-Z_((s))+2NaCI_((aq))to2Na_(2)-Z_((s))+MCI_(2(aq))`