Water Hardness

The presence of calcium, Magnesium salt, Carbonates, Sulphates in water is called causes of hardness of water. The water which contains these salts is called hard water.

The various salts present in water depend on the geological formations through which the water has flowed. These salts are mainly the carbonates (CO₃^2- ), hydrogen carbonates or bi-carbonates ( HCO₃^- ), Sulphates ( SO₄^2- ) and chlorides ( Cl^- ) of calcium ( Ca²⁺), magnesium (Mg²⁺) . Although calcium and magnesium carbonates in limestone are relatively insoluble in water. So in this reasons, water hardness can be divided into two ways-

1) Temporary hardness :  Ca(HCO₃)₂ , Mg(HCO₃)₂ , Fe(HCO₃)₂  

                                            

2) Permanent hardness :  CaCl₂ , CaSO₄ , Ca (NO₃)₂ , MgCl₂ , MgSO₄ , 

                                              Mg(NO₃)₂  

This water hardness causes some serious consequences in a textile dyeing and finishing industries and these are -

• Precipitation of soaps. 
• Redeposit ion of dirt and insoluble soaps on the fabric being washed , this can cause yellowing and lead to uneven dyeing and poor handle.
• Precipitation of some dyes as calcium and magnesium salts.
• Scale formation on equipment and in boilers and pipelines.
• Reduction of the activity of the enzymes used in washing.
• Incompatibility with chemicals in finishing recipes and so on.

Removal Of Water Hardness

There are mainly three methods by which hardness of water is removed in  Industrial scale. They are:-

1. Lime-soda process.
2. Base Exchange process (Permutit process).
3. Demineralization process.