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Increasing demands and decreasing supplies of high quality water sources have led to the use of alternative water sources for potable supplies; with new water sources bringing new treatment complications. Ion exchange (IEX), frequently used for water softening, has potential for dissolved organic matter (DOM) removal. Currently chloride-form resins are used for most IEX processes that target DOM, which generates a concentrated brine solution that is difficult to dispose. Work done by the authors has demonstrated that bicarbonate-form resins are as effective at removing DOM, without producing brine that is difficult to dispose of. Despite the potential of bicarbonate-form IEX, little published work exists exploring it.
It is well known that many divalent cations form precipitates in the presence of carbonates. The goal of this work is to quantify the fouling potential of bicarbonate-form resins in the presence of divalent cations. To explore the fouling potential, resins will treat solutions containing Ca2+, Mg2+, or Co2+, which have carbonate species with varying solubility products. DOM removal was expected to decrease with increasing solubility product due to precipitation causing fouling of fixed charged sites on the resin surface, however preliminary results with Ca2+ and Mg2+ do not show this. It is believed ion size and subsequently the ion’s ability to enter the pore volume impacts the fouling potential. Resins will be used and regenerated multiple times to explore how the progressive fouling of resins impacts the capacity of the resin and the kinetics of the IEX process.
This study is expected to show the impact of divalent cations on bicarbonate-form IEX, which will provide new information about the water chemistry conditions that are favorable for bicarbonate-form IEX. In addition, this study will also provide information on the impact of ion size and pore size on the fouling potential of IEX resins.
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