Ion Exchange Resin Selection Research In Electrodeionization Process

As an environmental friendly and energy-saving technology, EDI has broad prospects of development. EDI device is similar to electrodialysis device which filled with ion exchange resins in the form. It can achieve continuous deionization and continuous electric regeneration of ion exchange resins under electric filed effect. EDI, with the advantages of ion exchange and electrodialysis, not only solve the problem of environmental pollution by chemicals, but have higher utilization of water resources.At present, with the continuous improvement of the water quality requirements of various fields, EDI product water has also been more stringent standards. Key question to improve the EDI equipment product water quality is how to remove weak electrolytes from pure water completely. Therefore, weak electrolytes removal has become one of the emphasis studying direction in the field of pure water preparation. EDI technology mainly includes three aspects essentially:ion absorption by ion exchange resins、ion selective migration under the action of direct current ion exchange resins regeneration. These three aspects are directly related with ion exchange resins. Ion exchange resins serve as an important medium and bridge for the whole EDI process and guarantee the continuous electrodeionization procedure based on electric regeneration function. So, the performance of ion exchange resins paly important role in EDI device.This paper starting from the basic nature of the ion exchange resins, studied the different skeleton structure ion exchange resins adsorption isotherm of weak electrolytes、the maximum adsorption capacity and adsorption kinetics curves. Meanwhile, examined the removal effect of weak electrolytes under electric filed. The experimental results were as follows.1. In the absence of electric field, the adsorption characteristics of ion exchange resins for weak electrolytes mainly:a). in dilute solution, the adsorption properties of strong acid cation exchange resin to weak electrolyte NH4+had nothing to do with its skeleton feature; b). maximum adsorption capacity of gel-type resin for weak electrolyte NH4+was significantly higher than the macroporous resin; c). adsorption kinetics curves of gel-type resin reached equilibrium faster than that of macroporous resin and had higher equilibrium absorption capacity than macroporous resin; d). macroporous strongly basic anion exchange resin has better adsorption characteristics for weak electrolyte SiO32-than gel-type strongly basic anion exchange resin; e). maximum adsorption capacity experiments of two type anion exchange resin for weak electrolyte SiO32-did not show any obvious characteristics; f). macroporous anion exchange resin had more excellent adsorption properties for weak electrolyte SiP32-than gel-type anion exchange resin.2.Observed adsorption characteristics of the different skeleton types of resin for weak electrolyte ions in electric field. Main conclusions are as follows:a). The current growth rate of two types ion exchange resin for weak electrolyte processing system was increased With the increase of voltage, and the growth trend are similar; b). Action time had same influence on resin adsorption of weak electrolyte. Specifically, weakly ionized impurity concentration in produced water decreased at first, then had a slight increase, and finally achieve a dynamic equilibrium process; c). When mixing ratio of anion macroporous exchange resin and cation macroporous exchange resin was2:1, the removal of NH4+ions was the best, while the mixing ratio of anion gel-type exchange resin and cation gel-type exchange resin were1:1and1:2, the removal of NH4+ions was better than other ratio; d). When mixing ratio of anion macroporous exchange resin and cation macroporous exchange resin were1:1and2:1, the removal of SiO32-ions were better than other ratio, while the mixing ratio of anion gel-type exchange resin and cation gel-type exchange resin were1:1and1:2, the removal of SiO32-ions were better than other ratio.This experiment had reference value to the chioce of ion exchange resin in EDI process.