Electrodeionization Process For Heavy Metal Removal From Electroplating Wastewater

Nowadays electroplating is one of the most polluting industries all over the world. As being the main heavy metal pollutant source, electroplating wastewater would, if it discharged without treatment, not only pollute the waters and destroy the water environment but also lead to the great waste of water resources and expensive metals. Though many technologies such as chemical precipitation, biological method, ion exchange and electrodialysis (ED) can be used to remove the metal ions from the wastewater, they also have their own disadvantages. For these reasons, electro-deionziation (EDI) in this paper combining the advantages of the ion exchange and ED is a polishing process for electroplating wastewater without the polarization problem in the ED. Therefore, it will be a promising technology in the field of water purification.The problem using conventional EDI for the metal removal from electroplating wastewater is that hydroxide deposit in the interface of ion exchange resins or in the surface of ion exchange membrane would affect the stability of the process. By rearranging the membranes and assembling the cation exchange resins and anion exchange resins separately, it was found that the ionic product of the nickel ion and the hydroxyl ion is far lower than the solubility product constant. According to the solubility product principle, there is no nickel hydroxide precipitation in the concentrate compartment. Furthermore, by investigating the effect of voltages on the migration rate of the nickel ions under the electric field, we found that nickel ions transfer at higher rate by lower electric energy consumption when the applied voltages are 20V. After 3 hours, the regeneration efficiency is 50%.Finally, the comparison is made between the process of ion exchange and EDI for the purification of the simulated electroplating with the nickel ion concentration of 100 mg L^-1 which exhibits the merits of the latter. Moreover, the performance is evaluated in terms of percent extraction and current efficiency, respectively. We calculated the percent extraction is larger than 98% and the average current efficiency is 34%.This paper shows that EDI is advance and steady process, which can be used for the purification of the electroplating wastewater and recycle the concentrate containing heavy metal ions. The further application of this method can realize the closed-loop of electroplating wastewater so that it is favorable for the economic development and environmental protection.