Define soft water | What is water softening? State the name of method of water softening | Describe the base exchange process for softening hard water?

Define soft water?

The water which does not contain H CO3-, Cl-, SO42- salt of Ca2+, Mg2+, Fe2+, Al3+ & form foam easily by reacting with soap is called soft water e.g. Rain water.

What is water softening? State the name of method of water softening?

WATER SOFTENING: To remove the impurities of hard water by some desirable process is called water softening.

WATER SOFTENING PLANT / METHODS OF WATER SOFTENING:

1.         soda lime process.

2.        Base exchange process (permutit).

3.         Demineralisation.

4.        Soda alum.

5.         Aeration.

6.        Chelation on sequestration.

7.         Calgon process.

Describe the Base Exchange process for softening hard water?

This method depends upon the use of zeolite or base exchange complexes.

The zeolites are hydrated silicates of Na & Al with a generated formula- (Na2O)x (Al2O3)y (SiO2)z (H2O)n

When zeolites or base exchange complexes are brought in contact with hard water, following reaction

For temporary hardness-

Ca(HCO3)2 + Na2O.Z → CaO.Z + Na2CO3 + H2O

Mg(HCO3)2 + Na2O.Z → MgO.Z + Na2CO3 + H2O

For permanent hardness-

CaSO4+ Na2O.Z → CaO.Z + NaSO4.

MgSO4+ Na2O.Z → MgO.Z + NaSO4.

In water Z is an abbreviation for the Al2O3.SiO2.H2O part of zeolite. The soft water obtained from this Base Exchange process is of 0 – 20° hardness or

Levelness. After a long time the whole of the Na in Base Exchange substance is replaced by Ca or Mg. it is said to be exhausted because it will not soften any hard water more. Then it has to be generated.

Regeneration: CaO.Z + 2NaCl → Na2O.Z + CaCl2

The CaCl2 & residual NaCl are washed away & the regenerated Na2O.Z can be used to soften the hard water again.