Investigation on removal of hardness ions by capacitive deionization (CDI) for water softening applications

Seo, Seok-Jun; Jeon, Hongrae; Lee, Jae Kwang; Kim, Gha-Young; Park, Daewook; Nojima, Hideo; Lee, Jae-Young; Moon, Seung‐Hyeon

doi:10.1016/j.watres.2009.10.020

Cited by 392 publications

(171 citation statements)

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“…The complex interplay of these parameters may also explain the contradictory results on ion selectivity in the CDI literature [10,12,13,14,18]. To analyze these experiments in detail a full two-dimensional dynamic multicomponent CDI model is required including also proton transport [9,68] and the pH dependence of the ionic composition in those cases that amphoteric ions such as bicarbonate anions were used.…”

Section: Discussion Of Non-linear Theorymentioning

confidence: 99%

“…Remarkably, all this time, up to the end of the adsorption step, the Ca 2+ -concentration remains clearly below its inlet concentration of c in,Ca =1 mM, whereas the Na + -concentration increases to beyond its inlet concentration of c in,Na =5 mM and stays above c in,Na until the end of the adsorption step, a phenomenon also observed in ref. [18]. This behavior is a clear signature of a replacement process, in which the composition of the EDLs, initially predominantly containing Na + , is slowly modified toward the final equilibrium composition which is dominated by Ca 2+ .…”

Section: Dynamic Experimentsmentioning

confidence: 94%

“…Interestingly, the literature on CDI using mixtures of ions presents apparently contradictory results for the preference of the system to either adsorb monovalent ions, or divalent ions. Enhanced divalent ion adsorption has been reported [10,13,18], enhanced monovalent ion adsorption [12], as well as the absence of a clear preference in either direction [14].…”

Section: Introductionmentioning

confidence: 94%

“…In commercial desalination technologies, such as reverse osmosis and multistage flash distillation, freshwater is produced at relatively high energy cost and often requires re-mineralization for human consumption. For brackish water or wastewater it can be advantageous to use a different type of technology, namely techniques where ions are removed from the feed water under the influence of electrical field effects, such as in electrodialysis [8,9], capacitive deionization [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28], membrane capacitive deionization [29][30][31][32][33][34], desalination using microchannels [35], batteries [36], microbial desalination cells [37] and wires [38]. Such techniques have the potential to be energy-efficient as they focus on the removal of the (often relatively few) ions in the water to obtain freshwater in this way.…”

Section: Introductionmentioning

confidence: 99%

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Time-dependent ion selectivity in capacitive charging of porous electrodes

Zhao

Soestbergen

Rijnaarts

et al. 2012

Journal of Colloid and Interface Science

233

182

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In a combined experimental and theoretical study we show that capacitive charging of porous electrodes in multicomponent electrolytes may lead to the phenomenon of time-dependent ion selectivity of the electrical double layers (EDLs) in the electrodes. This effect is found in experiments on capacitive deionization of water containing NaCl/CaCl 2 mixtures, when the concentration of Na + ions in the water is 5 times higher than the Ca 2+ -ion concentration. In this experiment, after applying a voltage difference between two porous carbon electrodes, first the majority monovalent Na + cations are preferentially adsorbed in the EDLs, and later they are gradually replaced by the minority, divalent Ca 2+ cations. In a process where this ion adsorption step is followed by washing the electrode with freshwater under open-circuit conditions, and subsequent release of the ions while the cell is shortcircuited, a product stream is obtained which is significantly enriched in divalent ions. Repeating this process three times by taking the product concentrations of one run as the feed concentrations for the next, a final increase in the Ca 2+ /Na + -ratio of a factor of 300 is achieved. The phenomenon of timedependent ion selectivity of EDLs cannot be explained by linear response theory. Therefore, a nonlinear time-dependent analysis of capacitive charging is performed for both porous and flat electrodes. Both models attribute time-dependent ion selectivity to the interplay of the transport resistance for the ions in the aqueous solution outside the EDL, and the voltage-dependent ion adsorption capacity of the EDLs. Exact analytical expressions are presented for the excess ion adsorption in planar EDLs (Gouy-Chapman theory) for mixtures containing both monovalent and divalent cations.key-words: water desalination; porous electrode theory; capacitive (non-faradaic) electrochemical cells; electrostatic double layer theory.2

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Section: Discussion Of Non-linear Theorymentioning

confidence: 99%

Section: Dynamic Experimentsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Time-dependent ion selectivity in capacitive charging of porous electrodes

Zhao

Soestbergen

Rijnaarts

et al. 2012

Journal of Colloid and Interface Science

233

182

View full text Add to dashboard Cite

show abstract

“…Ion-exchange membranes have become widespread as diaphragms in diaphragm electrolyzers [12][13][14]. The use of ion-exchange membranes complicates design and operation of electrolyzers.…”

Section: Literature Review and Problem Statementmentioning

confidence: 99%