Kyeong-Ho Yeon

Removal of chromium from water and wastewater by ion exchange resins.

Removal of chromium from water and wastewater is obligatory in order to avoid water pollution. Batch shaking adsorption experiments were carried out to evaluate the performance of IRN77 and SKN1 cation exchange resins in the removal of chromium from aqueous solutions. The percentage removal of chromium was examined by varying experimental conditions viz., dosage of adsorbent, pH of the solution and contact time. It was found that more than 95% removal was achieved under optimal conditions. The adsorption capacity (k) for chromium calculated from the Freundlich adsorption isotherm was found to be 35.38 and 46.34 mg/g for IRN77 and SKN1 resins, respectively. The adsorption of chromium on these cation exchange resins follows the first-order reversible kinetics. The ion exchange resins investigated in this study showed reversible uptake of chromium and, thus, have good application potential for the removal/recovery of chromium from aqueous solutions.

Studies on adsorptive removal of Co(II), Cr(III) and Ni(II) by IRN77 cation-exchange resin

The adsorption of cobalt, chromium and nickel from aqueous solutions on IRN77 cation-exchange resin has been studied comparatively. The percentage removal of cobalt, chromium and nickel was examined by varying experimental conditions, viz. dosage of adsorbent, pH of the solution and contact time. It was found that more than 95% removal was achieved under optimal conditions. The adsorption capacity (k) for cobalt, chromium and nickel were calculated from the Freundlich adsorption isotherm. The adsorption of cobalt, chromium and nickel on this cation-exchange resin followed the Lagergren kinetic model. Also the competitive adsorption of multi-metals onto the IRN77 resin was studied. The studies showed that this cation-exchange resin can be used as an efficient adsorbent material for the removal of cobalt, chromium and nickel from water and nuclear power plant coolant water.

Electrochemical characterization of ion-exchange resin beds and removal of cobalt by electrodeionization for high purity water production

The characterization of three cation exchange resins, IRN77, SKN1, and IR120, for the removal of cobalt ions from an aqueous solution by electrodeionization (EDI) was studied. The study includes investigation of resin beds in terms of their ion exchange capacity, electrical conductivity, and zeta potential. The conductivity of a resin bed was analyzed using a porous-plug model to understand the current path. From the experiments, more than a 97% cobalt ion removal was achieved under optimal conditions. Furthermore, production of ultrapure water with a two-stage EDI process was tested for the reuse of treated water.

Effects of the Operating Parameters on the Reverse Osmosis-Electrodeionization Performance in the Production of High Purity Water

An RO-CEDI (Reverse osmosis-continuous electrodeionization) hybrid process was investigated to produce high purity water. The RO system, with an effective membrane area of 1.1 m2, was operated using tap water with conductivity of 64 μs·cm−1, and the CEDI system experiments were carried out in a cell-pair stack consisting of 3 compartments. During the parametric study of the RO-CEDI hybrid system, the optimal operating conditions were determined based on the water purity. The electrical resistivity and water dissociation of the ion exchange resins and ion exchange membrane were verified as the key mechanisms of the CEDI system in the water purification. The produced water met the quality requirements as a make-up water in a nuclear power plant with a resistivity of 10–16.7 MΩ·cm.

Transport Characteristics of Co2+ Through an Ion Exchange Textile in a Continuous Electrodeionization (CEDI) System Under Electro‐Regeneration

Abstract The transport of cobalt ion in a continuous electrodeionization (CEDI) system was investigated in terms of electrochemical properties of ion exchange textile. The porous plug model and an extended Nernst‐Plank equation were applied to describe the transport of Co2+ through an ion exchange textile. The transport characteristics of Co2+ during CEDI operation suggested the transport mechanism was due mainly to the increased current induced by the high conductivity in the ion exchange textile, not accelerated ionic mobility. This study suggested the important parameter for the high performance of the CEDI system is the conductivity of the ion exchange media.

A Study on Removal of Cobalt from a Primary Coolant by Continuous Electrodeionization with Various Conducting Spacers

The production of high purity water in the primary coolant of a nuclear power plant was investigated using a CEDI process with three ion-conducting spacers, i.e., ion-exchange resin (IX), an immobilized ion-exchange polyurethane resin (IEPU), and an ion-exchange textile (IET). The spacers were characterized by varying experimental conditions, e.g., dosage of adsorbent, pH of the solution, contact time, and the porous-plug model. The CEDI stack was assembled as a bed layered with the cation-exchange and anion-exchange materials. The stack configuration was designed to prevent a reaction between the metal ions and hydroxide ions. The performance of the CEDI operation with the layered bed showed more than 99% removal of the ions at a current efficiency ranged from 18 to 24%. In this study, the feasibility of using the CEDI in operations for the removal of heavy metals present at very low concentrations was successfully demonstrated.

Preparation and Characterization of Immobilized Ion Exchange Polyurethanes (IEPU) and Their Applications for Continuous Electrodeionization (CEDI)

Immobilized ion-exchange polyurethanes (IEPU) were prepared as ion conducting spacers in continuous electrodeionization (CEDI) for the treatment of a synthetic primary coolant. Ion exchange resins were immobilized by using allophanate/biuret cross-linking in preparation of polyurethane. Synthesized IEPU was characterized in terms of mechanical strength, ion exchange capacity (TEC), electrical conductivity and the porous plug model, which schematically represents the transport pattern through the IEPU. CEDI was carried out in a laboratory scale with an effective area of 20 cm2. The CEDI operation with a layered bed configuration showed the main removal mechanism of cobalt ion was dependent on the active surface area between ion conducting materials. The performance of the CEDI operation showed over 98% removal of cobalt ions, suggesting the feasibility of IEPU as ion conducting spacers in a CEDI system.

Removal of nickel from water and synthetic nuclear power plant coolant water by ion exchange resins

A method for the removal of nickel from waste water by adsorption process on ion exchange resin was studied. The percentage removal of nickel depends upon the contact time, pH and dose of adsorbent. Adsorption of nickel on ion exchange resins obeys Freundlich adsorption isotherm. The applicability of Lagergren kinetic model has also been investigated. In order to understand the adsorption behavior of nickel, a number of batch experiments were conducted at various pH values. The results show that the adsorption is maximum in the pH range 2 to 8. The studies showed that the ion exchange resins IRN77 and SKN1 can be used as an efficient adsorbent material for the removal of Ni(II) from water and coolant water.

Surface modification and use of polymer complex agents to mitigate metal crossover of anion-exchange membranes

The facile surface modification of a commercial anion-exchange membrane (i.e., Neosepta-AFX, Astom Corp., Japan) was investigated with brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO), which had non-charged polar groups, and its quaternized form (QPPO) to improve the acid recovery efficiency in diffusion dialysis (DD). By coating a thin layer of BPPO on the membrane surface, the significant changes in the surface compactness and charge density were observed while the electrochemical properties were mostly maintained. From the DD experiments, it was revealed that the membrane modified with 1 wt% BPPO exhibited the moderate acid permeability as well as the highest acid selectivity (KAcid/KFe3+=48.81), which is more than double compared with that of the pristine membrane (KAcid/KFe3+=22.48) among the tested membranes. The electron-rich polar groups contained in BPPO are believed to provide moderate proton transport while the reduced swelling property of the membrane surface can effectively mitigate the crossover of metal cations. In addition, the acid selectivity (KAcid/KFe3+=30.69) was largely improved by using small molecular weight poly(ethyleneimine) (PEI, Mn=1800) with a small content (in the range of 1-5 wt%) as a solution additive for the growing size of metal species by the formation of polymer-metal complexes.

A Cyclic Voltammetric Study of Electrodes for Reverse Electrodialysis

In this study, the electrochemical investigation of various electrodes for reverse elec- trodialysis using potassium ferrocyanide and potassium ferricyanide as a redox system was car- ried out. Cyclic voltammetry was the employed method for this electrochemical study. From the results of cyclic voltammograms for various electrode materials, i.e., Au, Vulcan supported Pt, activated carbon, carbon nanofiber, Vulcan, the Vulcan electrode showed the lowest over- potential, but the Pt electrode having slightly higher overpotential obtained slightly higher anodic and cathodic current densities for the Fe(CN)6 4 � /Fe(CN)6 3 � redox couple. The cyclic vol- tammograms for the Vulcan electrode confirmed very good electrochemical reversibility and kinetic behavior. As a result, among the electrode materials, the Vulcan electrode is the most promising electrode material for reverse electrodialysis.