How to Remove Permanent Hardness of Water?

Permanent hardness of water occurs because of the presence of CaCl₂, MgCl₂, CaSO₄, MgSO₄ compounds. To permanently remove the hardness of water we will use certain chemical methods. These methods are discussed below:

By Using of Washing Soda

In this method we add washing soda i.e., Na₂CO₃ ·10H₂O to hard water. The washing soda converts soluble chlorides and sulfates of calcium and magnesium into insoluble salts. The reactions are:

CaCl₂ + Na₂CO₃ → CaCO₃ + 2NaCl

MgCl₂ + Na₂CO₃ → MgCO₃ + 2NaCl

CaSO₄ + Na₂CO₃ → CaCO₃ + Na₂SO₄

MgSO₄ + Na₂CO₃ → MgCO₃ + Na₂SO₄

These CaCO₃ and MgCO₃ can be removed from the water by filtration. After filtration we get Ca⁺² and Mg⁺² ions free water which is the soft water.

Calgon’s Method

In this method we add Calgon i.e., Sodium Hexametaphosphate (Na₆P₆O₁₈) to water. In this reaction, Ca⁺² and Mg⁺² ions of hard water displace two Na⁺ ions of Calgon, resulting in the removal of calcium and magnesium minerals from water and addition of sodium ion from Calgon into the water. After this reaction the water becomes soft. The chemical reactions are:

Na₆P₆O₁₈ → 2Na⁺ + Na₄P₆O₁₈ ^2-

Mg²⁺ + Na₄P₆O₁₈ ^2- → Mg Na₄P₆O₁₈

Gan’s Permutit Method

In this method we use Zeolite or Sodium Aluminum Ortho Silicate i.e., Na₂Al₂Si₂O₈ ·KH₂O to remove hardness from water permanently. The reaction is:

Na₂Al₂Si₂O₈·KH₂O + Ca⁺² → 2Na⁺² + CaAl₂Si₂O₈·KH₂O

Ion-Exchange Resins Method

To remove permanent hardness of water we also use ion-exchange method. In this method we add synthetic ion-exchange resins (RNa⁺) or Zeolite i.e., Sodium Aluminum Silicate to the water, which is insoluble in water. In this reaction the ion-exchange process occurs between it and the Ca2+ or Mg2+ ions of the hard water. By this process the water becomes free from Ca⁺² and Mg⁺² ions and no longer remains hard.

Water is a crucial part of our lives. It is enriched with minerals that are important for our good health. Permanent Hardness of water is not only a theory but also a real-life problem we deal with every day in our lives. Knowledge of this concept helps the students relate the chemistry concepts to real-life problems and is also important for many exams like JEE and NEET. While temporary hardness is easy to eliminate by boiling, permanent hardness is not, so we have to use some chemical methods in this case. In this article, we will discuss in detail the methods of removing the permanent hardness of water, along with a few topics related to it.