DEIONIZATION AND THE MECHANISM INVOLVED

The process used for removal of all dissolved salts from water with the help of an ion-exchange resin system is referred to as deionization. It is based on Ion exchange method.
Deionization requires the flow of water through two ion-exchange resins (Cation exchange resin & Anion exchange resin) to remove all salt contents from raw water.

Raw water is passed through Cation Exchange Resin and Anion Exchange Resin respectively.
The passage of water through Cation Exchange Resin removes positively charged ions like calcium, magnesium etc, etc. The deionization process also removes metallic positive ions like Ferric ion Fe+++, Cu++, Al+++, etc, etc.
As the metallic ions in the water affix themselves to the ion-exchange resin while the resin releases its hydrogen ions on a chemically equivalent basis. A sodium ion (Na+) displaces one hydrogen ion (H+) from ion-exchange resin; a calcium ion (Ca++) displaces two hydrogen ions, a ferric ion (Fe+++) displaces three hydrogen ions, etc.

This exchange of hydrogen ions for metallic ions on an equivalent basis is a chemical necessity that permits the exchange material (resin) to maintain a balance of electrical charges.

At this point the deionization process is just half complete. While the positive metallic ions have been removed, the water now contains positive hydrogen ions, and the anions originally present in the raw water.
This partially treated water is now passed through Anion Exchange Resin where anions are displaced with hydroxyl ion ( HO-)
The produced water from such a two unit system (Cation Exchange Resin & Anion Exchange Resin) is ion-free water called as deionized water.
Raw water containing Ca (HCO3), Mg(HCO3)2, CaSO4, MgSO4, CaCl2, NaCl, SiO.H20 passed through Strong Acid Cation Exchange Resin.
Where R-Ca, R-Mg, R-Na, R-Fe are drained out.
While H+.Cl-, H+.S04--, H+. SiO2-- remains in the deionization line, which passes through a Strong Base Anion Exchange Resin.
R-SO4, R-Cl, R-HSiO3, R-HCO3 are drained out and DEIONIZED WATER is obtained in a stocker.

* R stands for Resin


In Our company, we have a Deionization Plant installed in our liquid section for our liquid syrup and suspension requirements.
The plant is simple one; containing two resin column
Cation Exchange Resin
Anion Exchange Resin

In addition to Ion Exchange Resin Columns, it is fitted with a Cartridge Filter and a Carbon Filter.
(A): WORKING UNDER IDEAL CONDITIONS:

Capacity to produce water after each regeneration: 6000 Liters
Quantity of HCl required in each regeneration: 23.919 Liters
Quantity of NaOH required in each regeneration: 11.960 Liters

COST PER REGENERATION:
Cost of HCl per Liter: Rs: 6.00
Cost of NaOH Solution per Liter: Rs: 22.86
Cost of HCl per regeneration: Rs: 143.51
Cost of NaOH per regeneration: Rs: 273.40
Total Cost of reagents per regeneration: Rs: 416.91

COST OF REGENERATIONS PER MONTH:
Total No. of regenerations required per month: 14
Total Cost of reagents per month: Rs: 5836.74


(B: WORKING UNDER CURRENT CONDITIONS:

Capacity to produce water after each regeneration: 4000 Liters
Quantity of HCl required in each regeneration: 17.085 Liters
Quantity of NaOH required in each regeneration: 8.542 Liters

COST PER REGENERATION:

Cost of HCl per Liter: Rs: 6.00
Cost of NaOH Solution per Liter: Rs: 22.86
Cost of HCl per regeneration: Rs: 102.51
Cost of NaOH per regeneration: Rs: 195.27
Total Cost of reagents per regeneration: Rs: 297.78

COST OF REGENERATIONS PER MONTH:

Total No. of regenerations required per month: 21
Total Cost of reagents per month: Rs: 6253.38
DIFFERENCE :
Total Cost of reagent per month: +416.64
This means, we are employing extra 416.64 rupees on regeneration of Deionization Plant per month.