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Bicarbonate-form anion exchange: Affinity, regeneration, and stoichiometry
Effect of multiple regeneration cycles on the removal efficiencies of (a) bicarbonate-form MIEX resin and (b) chloride-form
MIEX resin using synthetic NOM-containing model water. Showing that MIEX-HCO3 and MIEX-Cl have similar performance
over multiple regeneration cycles.
This research project was funded by an
Occidential Chemical Research grant and
faculty start-up funds awarded to THB. We
would like to thank Orica Watercare for
providing MIEX resin and Dr. Joe Delfino
for providing SFR NOM. Christopher A. Rokicki
(Ph.D., 2013)
Dr. Treavor H. Boyer
Overview and Objectives
The use of previously underutilized water sources for potable water supplies has brought about many new challenges for water
treatment engineers. Magnetic ion exchange (MIEX) is a technology that allows for the targeting removal of natural organic
matter (NOM) from water sources. Currently anion exchange resins such as MIEX are used predominantly in the chloride-form.
The use of a chloride-form resin leads to increased chloride concentration in treated water and thus a potential increase in
corosivity. Additionally, chloride-form resins generate a saline brine solution that is difficult to dispose. Bicarbonate-form resins
may not have these issues, but there is limited literature exploring the use of bicarbonate-form anion exchange. The objective of
this research was to determine whether or not bicarbonate-form anion exchange is as effective as chloride-form resin at removing
inorganic anions and NOM form simulated naturals waters. Individual objectives were to 1) determine bicarbonate-form anion
exchange’s affinity for common natural water anions; 2) investigate impact of repeated regeneration of bicarbonate-form resin;
and 3) investigate the stoichiometry of bicarbonate-form anion exchange.
Conclusions
Fresh MIEX-HCO3 resin showed very similar removals of tested anions as fresh MIEX-Cl resin.
Fresh MIEX-HCO3 resin and virgin MIEX-Cl resin showed greater removal of inorganic anions and NOM than
corresponding regenerated resins. Nevertheless, sodium bicarbonate had approximately the same level of regeneration
efficiency as sodium chloride when both anions were used at a concentration 10 times the equivalent capacity of MIEX
resin.
The selectivity sequence for MIEX resin was UV254-absorbing substances > DOC > sulfate > nitrate > bicarbonate ~
chloride.
CO2 gas is a potential technique for innovative regeneration of bicarbonate-form anion exchange resin because it does
not require salt.
The stoichiometry of chloride-, nitrate-, and sulfate-form MIEX resin followed ideal ion exchange behavior. In
contrast, the stoichiometry of bicarbonate-form MIEX resin did not follow predictable ion exchange. It appears that
resin-phase bicarbonate is deprotonating and resulting in a mixture of bicarbonate and carbonate mobile counter ions.
Bicarbonate- and chloride-form MIEX resin showed clear ion exchange stoichiometry for NOM removal over multiple
regeneration cycles.
Rokicki, C.A., Boyer, T.H., 2011. Bicarbonate-form anion exchange: Affinity, regeneration, and stoichiometry. Water Research
45 (3), 1329 -1337. DOI: 10.1016/j.watres.2010.10.018
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Treavor H. Boyer, Ph.D. ~ Assistant Professor ~ Department of Environmental Engineering Sciences ~ University of Florida
[email protected] ~ 352.846.3351 ~ www.ees.ufl.edu/homepp/boyer ~ www.twitter.com/WaterWeUpTo
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a. MIEX-HCO3 UV254
DOC
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NO3-
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