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12.28 CHAPTER TWELVE

Radioactive Iodine. Radioactive iodine has a very high affinity for strong base resins
and can be removed easily and efficiently. In nonradioactive scenarios, the strongly ba-
sic resins would be regenerated. In a radioactive scheme, a nonregenerable approach would
be taken using the same kind of selective resin used for nitrate, perchlorate, and uranium.
This could be the better economic choice depending on the water analysis, disposal, and
resin purchase price costs. Fortunately, in almost all cases, these resins can be interchanged
in the same equipment that, except for disposal-related processes, is a standard design.

Radioactive Uranium. The concentration in water would likely be so small and the
throughput capacity of the ion exchange resin so high that a nonregenerable system is the
most likely treatment process, using either ordinary strongly basic nitrate selective resins
or recently developed specialty resins with even higher preference for monovalent ions
like nitrate, perchlorate, and uranium carbonate. Throughput capacities would be similar
or identical to those of "ordinary radioactive" uranium removal for ordinary resins and
potentially up to several thousand times higher with the latest developments. However,
the radiation level in the resin could become a limiting factor so that ordinary resin, in
some cases, may well have the same capacity as the superselective ones when operated
under limited-dose scenarios. The biggest difference lies in the added cost of disposal of
the spent resin or regenerants as hazardous/radioactive wastes. For radioactive resins, dis-
posal costs are approximately 3 times their purchase price (as of March 2003) for nitrate
selective anion exchangers. Uranium from nuclear wastes, such as reactors, is several or-
ders of magnitude more radioactive than the uranium loaded into the reactor. The normal
isotope mix of enriched uranium is sufficiently low that the workers who loaded most of
the original uranium into nuclear reactors wore no protective garments except gloves. That
was to protect the fuel rods from human oil deposits that could later char and become a
corrosion site. The same fuel rods, when spent, could easily kill the worker who tries un-
loading it the same way due to the different isotopes formed during the nuclear service
cycle. Uranium and plutonium are not normally present in wastewater from nuclear plants,
but would be a problem if spent fuel was stolen and used to make a dirty bomb.

Uranium

At pH values above 6, uranium exists in potable water primarily as an anionic carbonate
complex that has a tremendous affinity for strongly basic anion exchange resins. Strongly
basic anion exchange resins can be used to remove uranium. The process has been tested
and found to be very effective at pH of 6 to 8.2. Higher pH values could result in ura-
nium precipitation, which makes the problem one of physical removal. Lower pH values
change the nature of uranium to a nonionic and/or cationic species. Tests have shown ef-
fective removal (over 95%) of uranium at pH as low as 5.6. But after the pH was reduced
to 4.3, the removal rate dropped to 50% and the run lengths (throughput capacities) were
reduced by over 90%! It has been shown that sudden changes in pH of the influent wa-
ter to values below 5.6 results in dumping of previously removed uranium. Therefore, it
is important to keep the inlet water pH above 6 at all times. In situations where the pH
cannot be maintained above 5.6, other treatment methods should be considered.

Throughput Capacity. The uranium carbonate complex has a relative affinity for
strongly basic anion exchange resin that is over 100 times greater than any common ions,
including the divalent ions such as carbonates and sulfates. At the pH levels associated
with potable water applications (6.0 to 9.0), the carbonate ion is negligible as it exists pri-
marily as the bicarbonate species, which is monovalent. Therefore, the sulfate ion is the
only potential competitor. The throughput capacity of a strong base anion resin for ura-