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12.24 CHAPTER TWELVE

TABLE 12.1 Perchlorate Selectivity Coefficients of
Various Anion Resins
Selectivity
coefficient
Type of resin C104 versus C1
Acrylic strong base, gel 5
Type I styrenic, gel 100-150
Type II, styrenic, gel 50-100
Tributylamine 2,000-4,000
Triethylamine macroporous styrenic 500-1,000

Recently, efficient regeneration schemes for these superhigh-perchlorate-capacity
resins are being developed that reduce chemical waste. One of the more promising
schemes is being patented (U.S. patent pending, 09/491,242). This process involves
the use of ferric chloride complexed with hydrochloric acid to form tetrachloroferrate
(FeC14-), an ion with exceptionally high affinity for anion resin (much higher than
perchlorate). By washing with water, the complex is broken, leaving the resin in the
chloride form, free of perchlorate and ready for the next service cycle. As little as two
bed volumes of the tetrachloroferrate solution are needed for complete regeneration of
even the bifunctional resins. When coupled to a perchlorate destruct system, the re-
generant solution can be reused without any perchlorate or regenerant sourced chlo-
ride being returned to the environment.
There are several possible destruct mechanisms for the perchlorate in waste brine and
reuse of the waste brine. However, most involve significant heat and/or pressure and are
therefore somewhat expensive and complicated. A simple process using a ferrous salt has
been developed to convert perchlorate back to chloride ions and oxygen, while at the same
time converting ferrous ions to ferric ions. This process is a low-temperature, inexpen-
sive adjunct to the technique of using tetrachloroferrate ion as a regenerant. This process
is also "patent applied for." The time interval between regenerations is much longer than
that for typical ion exchange systems. This should allow development of energy-efficient
approaches and smaller multicycle regeneration systems. These developments could tip
the balance in favor of using resins on a regenerable basis.
Flow sizing criteria for these resins tend to be the same as for normal regenerated
resins, 2 to 8 gpm/ft 3 of ion exchange resin (1- to 4-min EBCT). It has been reported
that some of the larger, very highly selective functional groups used in the bifunctional
resins are more flow-rate-sensitive than others. The second functional group is added
to compensate for this. All the selective resins can be operated at flow rates approaching
15 gpm/ft 3 (30-s EBCT). Some capacity is lost at higher flow rates. Flow rate sensi-
tivity will probably vary greatly among the different resin types. Also, extremely high
flow rates in traditional forms of ion exchange applications such as water softening
have led to bed compaction, plugging, and other problems; thus long-term design at
such high flow rates carries a significant risk of poor reliability and frequent mainte-
nance. As with all ion exchange systems, limits of oxidants, suspended solids, and
organic contaminants are necessary for long-term operation without fouling. Table 12.2
describes some of the resins and their suggested roles on perchlorate removal
applications.