Soft water is a desirable prerequisite for all textile wet processes, except for bleaching with solutions of hydrogen peroxide stabilized by sodium silicate. Modern synthetic detergents do not form precipitates in hard water containing calcium and magnesium ions so a certain degree of hardness is tolerable provided that other dyes and chemicals are not seriously affected by this. In general, however, if a textile wet processing mill is in a region where the water is hard, a softening pretreatment is essential for at least part of the water used. The objective of this is simply to reduce the concentration of the alkaline earth metals to a level at which the water has the desired quality. In many cases, the softening process may reduce the calcium and magnesium ion concentrations to zero.
Water softening is the removal of certain dissolved minerals (multivalent cations) in water that cause scaling in boilers, form deposits on pipes, and cause excessive consumption of soaps made from natural animal fats. There are different types of water softening process such as
- Demineralization (Ion-exchange)
- Lime softening.
- Chelating agents.
- Washing soda method.
- Distillation and rain water.
- Reverse osmosis.
In this article I will discuss demineralization process for water softening.
What is the Process of Demineralization of Water Softening?
Demineralization process is the modern industrial water softening process which is the removal of essentially all inorganic salts by ion exchange. Demineralization is important for water fed to very high pressure boilers. By this process the, It can be possible remove of hardness as well as remove of all dissolve salts i.e;. FeCO3, CaCl2. We can also say that demineralisation or deionization is the process of removing the dissolved ionized solids from water by ion exchange. The major portions of total dissolved solids (TDS) are mineral salts, such as calcium bicarbonate, magnesium sulfate, and sodium chloride. Mineral salts are composed of cations and anions. Since deionization requires the removal of all ions, both the negatively charged anions and the positively charged cations, then materials capable of attracting both are required. These materials are known as cation and anion exchange resins.
The demineralization plant consist of both cation and anion unit. Control over cation and anion unit is essential. Predetermined amount of resin bed are taken according to the composition of hard water. Demineralization process of water softening can be brought about in two ways:
- Hydrogen Cation exchange
- Anion exchange
A. Hydrogen Cation Exchange:
Cation resin can be in Hydrogen (R-SO3H) or Sodium form (R-SO3Na). Sulphonated resin (Cation acid resin) in Hydrogen form is used as cation exchanger for water softening.
CaCl2 + H2R –> CaR↓ + 2HCl
Ca(HCO3) + H2R –> CaR↓ + 2H2O + 2CO2
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B. Anion Exchange:
Amino resin (anion base resin) is used and produced HCl is removed.
HCl + HOR1 –> ClR1↓ + H2O (soft water)
We know, regeneration is done to get back the resins which are used to softening water are exhausted and we have to apply some acid and alkali to regenerate them again.
For step1, regeneration is performed by using acid. Less than 2% H2SO4 is used.
CaR + H2SO4 –> CaSO4 + H2R (regenerated resin)
For step2, regeneration is done by using 1% solution of NaOH.
ClR1 + NaOH –> NaCl + HOR1 (regenerated resin)
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Importance of Demineralization Process in Water Softening:
Demineralization process is an essential step in water softening, and it plays a crucial role in various industrial, commercial, residential applications and specially in textile wet processing industry. Demineralization involves the removal of mineral ions, particularly calcium and magnesium ions, which are responsible for water hardness. It contributes to cost savings, energy efficiency, and the overall reliability of water-dependent systems in various applications.
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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.