DOWEX Ion Exchange Resins WATER CONDITIONING MANUAL

Demineralization (Deionization) Process
H2SO4 or HCl is usually used for cation resin regeneration at a rate of 2 to 4 ppm for each ppm of cation
removed. Caustic soda (NaOH) is used at a rate of 1 to 2 ppm for each ppm of acid (e.g., HCl and H2SO4)
removed by a weak base anion resin, or 2 to 3 ppm for each ppm of either strong or weak acid anion
removed by a strong base anion resin. Mixed beds normally require 15–20% higher regenerant dosages
than individual beds.
In Table 10, a typical water sample is analyzed before any treatment and after each of the three main
steps in demineralization. The analyses indicate which constituents are removed from the water at each
stage of the process.
Constituent ppm as
Table 10. Results of treatment by the demineralization process.
Typical Raw
Water
Typical Strong
Acid Cation
Effluent after
Degasification
Typical Weak
Base Anion
Effluent after
Degasification
Typical Strong
Base Anion
Effluent
Calcium CaCO3 150 Nil Nil Nil
Magnesium CaCO3 50 Nil Nil Nil
Sodium CaCO3 50 0–5 0–5 0–5
Hydrogen CaCO3 0 100 0 0
Total electrolyte CaCO3 250 100 0–5 0–5
Bicarbonate CaCO3 150 0 0 0
Carbonate CaCO3 0 0 0 0
Hydroxide CaCO3 0 0 0 0–5
Sulfate CaCO3 50 50 0 0
Chloride CaCO3 50 50 0–5 0
Nitrate CaCO3 0 0 0 0
M Alk CaCO3 150 0 0–5 0–5
P Alk CaCO3 0 0 0 0–5
Carbon dioxide CO2 10 5 5 0
pH — 7.5 2.0 7.0 7–9
Silica SiO2 10 10 10 0–0.1
7.3 Equipment Required
A demineralization system may consist of a number of individual ion exchange units (e.g., a two-step
system would involve a cation vessel and an anion vessel) or a single vessel containing a mixture of
cation and anion exchange resins (mixed bed). Also required in any demineralization system are
appropriate piping, valves, chemical regenerant storage, flow controls, and other accessories properly
engineered for economical balance of resin capacity and chemical efficiency. The following illustrations
show the basic types of demineralization processes and which of the constituents is removed by each of
the demineralizing units.
DOWEX Ion Exchange Resins 37 Water Conditioning Manual