The presence of Calcium, Magnesium salt i.e bi-carbonates, sulphates, Chloride in water is responsible for hardness of water. The water which contains these salts is called hard water. These salts may precipitate some dyes during dyeing or form complexes resulting in dulling of shades. Other metal salts, such as iron and strontium, may also contribute to hardness, but they are generally present in smaller amounts as compared to calcium and magnesium. Water’s hardness is determined by the concentration of multivalent cations in the water. Hardness of water is measured by hardness measurement scale which is given below.
Two types of hardness may be distinguished, temporary and permanent. Temporary hardness arises from bicarbonates and can be removed simply by boiling, when the bicarbonates precipitate as carbonates.
Ca(HCO3)2 → CaCO3 + H2O + CO2
It is a contributory factor in the formation of scales in boilers, which are deposits, among other things, of calcium carbonate and magnesium hydroxide, the latter being a decomposition product of magnesium carbonate.
MgCO3 → Mg(OH)2 + CO2
Permanent hardness is associated with sulfates and chlorides of calcium and magnesium. These are highly soluble in water, and expulsion of dissolved gases makes no difference in their solubility. These require chemical treatment for their removal. Water from most sources has both temporary and permanent hardness, but the proportion of the two varies.
Problem Caused by Hard Water in Textile Wet Processing Industry:
In textile industry, specially in textile wet processing, water consumption is far greater than the amounts of fibers processed. It is the ubiquitous solvent for the solutions of chemicals used. Rinsing and washing operations alone consume enormous amounts of water. Steam is still the major heat-transfer medium for many processes and the quality of water fed to boilers is often critical. Any presentation of textile dyeing would be incomplete without some discussion of the quality of water required for textile wet processing, and of the treatment of waste water so that it can be discarded with minimum environmental impact. Hard water can create so many problems during wet processing from desizing to finishing in textile industry. So before using water in textile processing should ensure it is hard water or soft water.
The use of hard water in a textile wet processing industry can have some serious problems / consequences.
- Precipitation of soaps.
- Redeposition of dirt and insoluble soaps on fabric being washed. This can caused yellowing and lead to unlevel dyeing and poor handling.
- Precipitation of same dyes as Ca and Mg salt react with them.
- Scale formation on equipment and in boilers and pipelines.
- Reduction in activity of enzyme used for desizing.
- Decreased solubility of sizing agent.
- Coagulation of some types of printing paste.
- Hard water in desizing de-active enzymes and insolubilize size materials such as starch, PVA etc.
- In compatibility with chemical in finishing recipes.
- Hard water react with soap during scouring.
- Decomposition of belching bath.
- Ca2+ and Mg2+ ions of hard water react with dye molecules and precipitated the dye. As a result dyestuff are spoilt. Hence, uneven shade (depth of dyeing) of color is produced.
- Hard water cause problems in printing process like dyeing.
- In mercerization form insoluble melt oxide and reduce absorbency and luster.
- Hard water interfere with catalysts, cause resins and other additives to become non reactive, break emulsion and deactives soap.
Required Parameters of Water for Textile Wet Processing:
From the points of previous section, we saw that the hard water causes many problems in every process of textile wet processing. So, we have to use such water that is suitable for wet processing and don’t create any problem. Ideal quality of feed water for textile industry is:
- pH should be in the range of 7 – 8.
- Water should be odorless and colorless.
- Water hardness: maximum 5°dH.
- Solid content: <50 mg/L.
- Dissolved solids : <1 mg/L.
- Inorganic salts: <500 mg/L.
- Organic salts: <20 mg/L.
- Iron (Fe): <0.1 mg/L.
- Mn: <0.02 mg/L.
- Cu: <0.005 mg/L.
- Nitrate: <50 mg/L.
- Nitrite: <5 mg/L.
You may also like:
- Water Hardness Test Method
- Water Management in Textile Industry – An Overview
- Water Consumption in Textile Processing Industry
- What is Sequestering Agent? | Types, Mechanism and Uses of Sequestering Agents
- Hardness of Water in Textile Industry: Types, Reasons and Consequences
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.