25 May 2005
Exchange Process Result. When the anion exchange process is
combined with the hydrogen exchange process, the resulting final water will contain no
minerals. It has become deionized (also referred to as demineralized) by exchanging all
minerals to hydrogen hydroxide, HOH, commonly referred to as water and written as
Exchange Method. The two reactions can take place in separate vessels
(a "two-bed" deionizer), or the two ion exchange materials can be combined in a single
vessel (a "mixed-bed" deionizer).
High Silica Waters. Removal of silica and magnesium beyond what most
for regeneration. Optimum temperature is 49 oC (120 F) and should not exceed 60 oC
(140 F), as that temperature can damage the resin; however, few demineralizers are
designed for this application.
Deionization Process Use. The deionization process is not used at
government installations. It is required mainly for high-pressure boilers or high-purity
water use. The deionization process may also be used by the Navy for shore plants
providing steam or boiler feedwater to ships.
Anion Dealkalization. It may be necessary to treat water having low
hardness and high alkalinity to reduce the alkalinity (bicarbonate and carbonate). The
anion exchange process called "anion dealkalization" will remove alkalinity and other
anions (i.e., sulfates and nitrates). In most cases, the anion dealkalizer is used following
a hardness softener (i.e., it is located downline from the softener) because hardness, if
not previously removed, can precipitate in the anion resin bed and cause plugging.
Bicarbonate and carbonate (anions) are exchanged for chloride (anion) as illustrated by
the following reaction, where "Z" is the zeolite resin material:
2-188.8.131.52.1 System Regeneration. The system is regenerated with sodium chloride
(salt) as shown below. The regeneration will be more efficient and effective if the brine
used contains about 10% of the salt as caustic.
2-184.108.40.206.2 Equipment and Operation. The equipment and operation of such a
system is much the same as for a sodium ion exchange material system described in
paragraph 2-2.5.1. This process is illustrated in Figure 2-5.