Page 371 -

ION EXCHANGE APPLICATIONS IN WATER TREATMENT 12.29

TABLE 12.3 Difference in
Uranium Removal with Different
Sodium Chloride Concentrations
NaC1 Uranium
concentrations, % removed, %
4 47
5.5 54
11 75
16 86
20 91
Regenerant level approximately 22 lb/ft 3
of type I gel anion resin.

nium removal can conservatively be estimated as being 100 times the throughput to sul-
fate breakthrough. To maintain this capacity over many cycles, it is necessary to use suf-
ficient salt and at sufficiently high concentrations to regenerate the resin back to the chlo-
ride form.

Regeneration. To regenerate the uranyl carbonate ion from the resin, it is important that
the concentration of the regenerant at the resin bed be sufficiently high to reverse or re-
duce its relative affinity (compared to chloride) to workable levels, and to use enough re-
generant and contact time to complete the process. Sodium chloride is the most common
regenerant. Table 12.3 shows the difference in effectiveness of various concentrations
of salt.
At concentration above 20% a regenerant level of 15 lb/ft 3 is sufficient to ensure bet-
ter than 90% uranium removal. Leakage will remain low through the service cycle even
without complete regeneration because of the very high selectivity at the low ionic con-
centrations during the service cycle. Leakages are normally well below 1% for regenera-
tion levels of 15 lb/ft 3 of sodium chloride applied at concentrations of 10% or higher.
Other Regenerants. The chloride ion at neutral or low pH is the most commercially ef-
fective ion for the regeneration of uranium from anion resins. Neutral salts are usually
preferred because of environmental concerns and materials of construction considerations.
Regeneration with pure hydrochloric acid, though not recommended because of the na-
ture of hydrochloric acid and the added expense for corrosion-resistant equipment, shows
an even better efficiency than sodium chloride because of its low pH. Higher pH, such as
through the addition or use of alkalis such as sodium hydroxide or sodium bicarbonate or
sodium carbonate, would result in severely decreased uranium regeneration. At high pH
values, uranium tends to form Na2U207, a nonionized precipitate that stays in the resin
and interferes in subsequent service cycles.

TOC, Color, and Trihalomethane (THM) Precursors

These are usually caused by naturally occurring organics, which are the result of the nat-
ural decay of vegetable matter, primarily leaves, grasses, roots, and fallen branches. The
resulting soluble or colloidal dispersion of semisoluble matter is a mixture of fulvic and
humic acids, tannins, and lignins. These are primarily aromatic hydrocarbons with car-