Electrodeionization (EDI) is an efficient process for deep desalinating, which depends on the mechanism of water dissociation occurring on the surface of ion exchange membranes and resins. But when dealing with using it to treat the dilute heavy metal solutions, the water dissociation product, OH" ions, will combine with heavy metal ions to form metal-hydroxides precipitation and which would nonreversibly destroy the separation process. A coupled '"bipolar membrane-electrodeionization (BMEDI)" process was developed here. In the proposed process, the products of water dissociation occurring in the bipolar membrane can play the role of pre-acidification and restrain the water dissociation on the surface of resins as well. Thus the metal-hydroxides precipitation will be prevented and the resins can be regenerated. Using NiSO4 solution with Ni2+ ion concentration of 24 mg·L-1 to simulate the dilute heavy metal solution, the experiments of removing the heavy metal ions from the dilute heavy metal solution and collecting them in the neighbor chambers were conducted under constant current density. The results show that, after operating at 40 mA-cm"2 for 19 hours, the Ni2+ ion concentration in the concentrated solution could reach 743 mg·L-1, which gives a concentrating ratio of about 31, while the Ni2+ ion in the dilute stream is below the analysis limit and no Ni(OH)2 precipitation was observed in the stack.%电去离子(EDI)技术依靠离子交换膜和树脂表面自发的水解离特性实现深度脱盐功能,但处理含低浓度重金属离子溶液过程中,水解离产物OH-离子易与重金属离子生成金属氢氧化物沉淀,导致不可逆的破坏性影响.今将双极膜引入EDI膜堆,利用其内部的水解离产物实现预酸化和抑制树脂表面水解离功能,防止结垢并实现树脂再生.以含24 mg·L-1Ni2+的NiSO4溶液为原水,在恒工作电流密度下纯化低浓度NiSO4溶液同时回收Ni2+离子.结果表明,40mA·cm-2下浓缩运行19h后,浓缩液中Ni2+为743 mg·L-1,浓缩倍数约31,淡水出水中未检出Ni2+,膜堆内部无Ni(OH)2沉淀生成.
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