Construction Of The Ion Exchange Fabric-filled Electro-deionization Device And Its Application For Heavy Metal Ions Wastewater Treatment

Heavy metal ions are one of the main pollutants in the world. The existing treatmentmethods of the low concentrations of heavy metal ions wastewaters include chemicalprecipitation, adsorption, reverse osmosis, and electrodialysis, and they more or lesspresent some limitations. The electrodeionization (EDI) technique takes the advantage ofion exchange and electrodialysis, while it avoids the frequent chemical regeneration of ionexchange resins and the concentration polarization of electrodialysis. EDI technique hasfound its application for preparation of ultrapure water.With conventional EDI technique, the stability of electrodeionization is spoiled byhydroxide precipitants which form on the surface of ion exchange resins and membranes.In this thesis, a column-plate electrodeionization device was designed and assembled. Themain interesting issues were the removal of heavy metal ions and the reduction ofprecipitation by changing the structure of the membrane pairs，and substituting for ionexchange fabric, etc.This thesis successfully constructed column-plate electrodeionization device. After5-hour operation, the copper ion removal reached99.96%above. Based on the ionthree-zone removal mechanism, a device with three-pair membrane structure wasassembled.After90-hour running, the copper ion removal remained90%above.Compared with the empty concentrate chamber, the copper ion concentration of thedilute exit water for the device with resin-filled concentrate chamber maintained at0.1mg/L after80-hour running. Even after110-hour operation, the copper ion removal stillkept99.8%, significantly better than that of the empty concentrate.After100-hour operation, comparison study indicated that electrodeionization devicefilled with ion exchange fabric effectively slowed down precipitation on ion exchangeresins and membranes, and improved the long-time operation stability ofelectrodeionization. Nevertheless, the copper ions concentration of the dilute exit reached up to4.44mg/L after5-hour operation due to the bipolar membrane effect accidentlyoccurred between fabric and membrane.The current efficiency of ion exchange fabric filled horizontally electrodeionizationapparatus up to38%, better than that of the filled resin electrodeionization system.After long-term operation, a degradation behavior occurred on anion exchange resinsand membranes, but cation exchange ones were no changes.The horizontal filling ion exchange fabric could delay precipitation of hydroxide andenhance current efficiency, and this would improve the long time operation stability. It willbe expected the electrodeionization system has broad applications on treatment of heavymetal ions wastewaters.