Impurities in water

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The brightness of color, performance of dye, whiteness etc. depends on water used in wet processing. So, it is essential to know what type of water is suitable for wet processing. To know this first we should understand about the impurities in water. There are mainly four types of impurities in water:

1. Turbidity and color: Turbidity is the presence of small and large particles in water which are soluble in water. These particles may be inorganic (silica, calcium carbonate) or organic (fats, vegetable mater, micro-organism) in nature. Large particles are removed by sedimentation. Filtration is used for small particles.

Colors dissolve in water or colloidal organic mater disperse in water. These organic compound are not visible normally. A Tintometer is  used to measure the amount of color in water. 

Turbidity and water stain the fabric.

2. Ions of Heavy metals: Ions of heavy metals like iron, manganese, copper are harmful during wet processing. These causes following problems:

Act as catalyst in the decomposition of bleaching agents and cause activated attack with subsequent degradation of fibre.

Produce slight yellow color during scouring and bleaching and it is difficult to remove the color.

It may insolubilise the metal oxide during mercerization and reduce lusture, absorbency.

In the dyeing stage, metal ions may combine with some dyes and cause dulling of shade.

3. Alkalinity: Generally when water contains carbonate and bicarbonate then water shows alkalinity. Amount of carbonate and bicarbonate is measured by Titration method.

4. Hardness: The presence of calcium, magnesium salt i.e. bi-carbonates, sulphates, chloride in water causes the hardness of water. The water which contains these salts is called hard water. Hard water does not easily form lather with soap as the salt of calcium and magnesium react with soap to form insoluble organic salts. There are two types of water hardness:

  (a) Temporary hardness: Temporary hardness is due to the presence of bicarbonates of calcium and magnesium. The types of hardness is called temporary hardness as it can be removed by boiling.

  (b) Permanent hardness: It is due to presence of chlorides or sulphates of calcium and magnesium. This type of hardness is called permanent hardness. These salts do not decompose on boiling. So permanent hardness cannot be removed easily.