Question

HOW IS PERMANENT HARDNESS REMOVED?​

Answer 1

It is known that temperary Hardness can be removed thermal treatment. It is due to the presence of Calcium, Megnesium, carbonate and bicarbonate ions. Same way Permanent hardness is due to the presence of Calcium, Megnesium, Sulphate and Chloride ions.

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Answer 2

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Permanent Hardness of Water:

When the soluble salts of magnesium and calcium are present in the form of chlorides and sulphides in water, we call it permanent hardness because this hardness cannot be removed by boiling.

We can remove this hardness by treating the water with washing soda. Insoluble carbonates are formed when washing soda reacts with the sulphide and chloride salts of magnesium and calcium and thus, hard water is converted to soft water.

How to Remove Permanent Hardness of Water?

• Gan’s Permutit Method:

In this method, sodium aluminum ortho silicate known as permutit or zeolite is used to remove the permanent hardness of water.

Reaction: Na2 Al2 Si2 O8.KH2O + Ca++→ 2Na+ + Ca Al2 Si2 O8.xH2O

• Calgon’s Process:

In this method, sodium-hexa-meta-phosphate (NaPO3)6 known as Calgon is used. The hardness in water is removed by the adsorption of Ca++ and Mg++ ions.

• Ion Exchange Resin Method:

In this method, the permanent hardness of water is removed by using resins. Ca++/Mg++ ions are exchanged with Cl–, SO4-2 ions are exchanged with anion exchange resin (RNH2OH). Demineralized water is formed in this process.

⇒ 2RCOOH + Ca++ → (RCOO)2Ca + 2H+

⇒ RNH2OH + Cl– → RNH2Cl + OH–

⇒ H+ + OH– → H2O

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