Softening of water

The special treatment for removing dissolved impurities from water after it has passed through all other treatment processes is called Softening of water.

Water contains chlorides, sulfates, bicarbonates of calcium and magnesium. This water is called as hard water.

The hardness of water may lead:-

1. Consumption of soap for washing of clothes etc shall be more.

2. The quality of paper, textile, ice making, dyeing etc. may be affected.

3. It forms scale in boilers due to which the consumption of fuel would increase and also boiler tubes may have to be replaced frequently due to corrosion.

Types of Hardness:

Temporary hardness, 2. Permanent hardness.

1. Temporary hardness – It is generally due to the presence of CO₂ in water. It dissolves insoluble carbonates of Ca and Mg to form into soluble form of bicarbonates which are held in solution.

Ca (HCO₃)₂ ------ CaCO₃ + CO₂ + H₂O

This type of hardness is removed by boiling which drives off the carbon dioxide and thus converting bicarbonates into insoluble carbonates. Insoluble carbonates settle at the bottom as precipitate.

Permanent hardness – It is due to sulfates and chlorides of Ca and Mg. It can not be removed by boiling. It is removed by addition of Caustic soda or Soda ash.

MgSO₄ + Na₂CO₃ ------- MgCO₃ + Na₂SO₄

(Soda ash)

The degree of hardness as per Clark’s scale is expressed in terms of grains of CaCO₃ dissolved per gallon of water.