Hard Water

The water which contains bi-carbonates, sulphates, chlorides etc is called Hard Water.

Properties of Hard Water: The most important characteristics of hard water is reaction with soap. When soft water react with soap then it produced foam quickly but it hardness is present in the water and if soap added in that water drop by drop than at first soap will work to reduce the hardness but no foam will create. After a long time use of soap foam will create that means hardness reduce soap efficiency.

C₁₇H₃₅-COONa+CaSO₄ → (C₁₇H₃₅COO)₂ Ca↓+Na₂SO₄

When the whole of the hardness has been changed into insoluble calcium and magnesium compounds, further addition of soap will create lather and be available to function as detergents.

There is wastage of 1.7lb of soap per 1000 gallon of water.

Problem associated with Hard Water:

1. Scale formation in boiler.
2. Reaction with soap.
3. Reaction with dyestuff.
4. Corrosion of boiler.
5. Deposition on the goods during scouring.

Potential problem causes by hard water in textile process:

Process	Problem
Desiszing	It reduce work ability of different active desizing agent such as starch, PVA etc.
Scouring	Combine with soap precipite metal organic acid produce yellowing or off white shade, reducing cleaning efficiency and also reduce water absorbness and also reduce detergency power.
Bleaching	Mainly H2O2 is the main bleaching agent. But hard water decomposes in H2O2 in the bleach bath. That is H2O2 → H2O+[O]
Dyeing	Combine with dye reduce dyestuff power, changing their shade, insolubilize dyes, reduce dye diffusion.
Printing	Break emulsion, changing thickness, reduce viscosity and efficiency.

Problem associate with hard water in directly:

1. Scale formation in boiler: Temporary hardness is rapidly converted to calcium carbonate and magnesium hydroxide in a boiler and in time accumulated in the form of scale ion the inner surface of the shell or in the tube,

Ca(HCO₃) ↔CaCO₃+CO₂+H₂O

Mg(HCO₃)₂ ↔MgCO₃+CO₂+H₂O

MgCO₃+H₂O ↔ Mg(OH)₂+CO₂

Here, MgOH₂ and CaCO₃ formed scale in boilers.

2. Corrosion of boiler: Corrosion can be a serious cause of harm in boiler. Dissolved oxygen in the presence of CO₂ is a common cause of corrosion. CO₂ react with iron, forming ferrous carbonate which in turns tends to hydrolyse to ferrous hydroxide,

Fe+H₂O+CO₂ ↔FeCO₃+H₂

FeCO₃+H₂O ↔ Fe(OH)₂+CO₂