Question

Hardness forms deposits (scale) in plumbing, cause corrosion, and turns water in cloudy appearance. so it is often desirable to decrease the hardness level in water and wastewater treatment processes. Briefly describe two methods to reduce/remove hardness causing ions that are typically used in water and wastewater treatment systems.

Answer 1

Ans: Methods to remove hardness of water

1. Adding washing soda

2. Adding slaked lime ( Clark's process)

3. Calgon process

4. Ion exchange process

5. Chemical process of boiling hard water etc

1. Adding washing soda:

Calcium and magnesium ions present in hard water react with sodium carbonate to produce insoluble carbonates. The water nowas contains soluble and harmless sodium salts.

CaSO₄ + Na₂CO₃    CaCO₃ + Na₂SO₄

cause of permanent insoluble

hardness

MgCl₂ + Na₂CO₃ MgCO₃ + 2NaCl

Cause of permanent insoluble

hardness

2. Adding slaked lime

In Clark's process, slaked lime, Ca (OH)₂ is added temporary hard water. Insoluble calcium carbonate precipitateout and no longer produce hardness.

Ca (HCO₃)₂   + Ca(OH)₂      2CaCO₃   + 2 H₂O

slaked lime insoluble calcium

carbonate

Insoluble salts are filtered out.