Wednesday, May 16, 2012
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.
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| Demineralization Process of Water Softening |
Demineralization process of water softening can be brought about in two ways:
1. Hydrogen Cation exchange
2. Anion exchange
1. 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
2. Anion Exchange:
Amino resin (anion base resin) is used and produced HCl is removed.
HCl + HOR1 --> ClR1↓ + H2O (soft water)
Regeneration:
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 & 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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