Research Of Heavy Metal Wastewater Treatment By Electrodeionization Technologv

Heavy metal pollution was one of the most outstanding problem in environmental protection nowadays. As the environment protection level formulated by government enhanced, the processes of heavy metal wastewater treatment were forced to do great improvements. The electrodeionization technology (EDI) is confirmed to be an efficient, stable and environment friendly technology in low-concentration heavy-metal wastewater treatment for its own characteristics, which could meet the high environment protection levels and standards of wastewater discharging.However, the mass transfer efficiency and the phenomenon of scale formation of the processes above have been hindering their industrial promotion. Current researches have made o lot of effort and improvements to enhance the mass transfer efficiency and ease the phenomenon of scale formation of the processes, but they failed to make an effective combination of the improvements. Besides, the ways of design optimization for internal structure of existing EDI stack were too single. In this paper, a novel EDI stack was designed against these problems. And the typical electroplating rinse wastewater containing Ni2+was simulated and chose as the treatment object. Then, the influences of operation conditions on the performances of EDI process were discussed. Finally, on the basis of optimization of internal structure of the EDI stack, the long term stability of EDI device for the treatment of low-concentration heavy-metal wastewater was studied. The detail researches were as follows:1. Based on the existing researches on the optimization of internal structure of EDI stack and theoretical analysis, a novel EDI stack was well designed. The new one not only reasonably combines beneficial factors for mass transfer and inhibiting scale formation but is also equipped with anion and cation exchange resin with a certain ration in its concentrate departments.2. Study on the feasibility of EDI device, whose dilute departments filled with cation exchange resins, for the treatment of low-concentration heavy-metal wastewater. It was found that the EDI process could be effectively used for the removal of Ni2+in wastewater. And the effects of operating voltage, dilute flow rate, Ni2+concentration and pH of feed solution on the separation performances EDI processes were investigated. What’s more, the chief operating parameters of the technics were optimized under the conditions that the product water could meet the standards of heavy-metal wastewater discharging and the process could be stable and efficiently operated.3. Study on the effects of volume ratio of anion and cation exchange resin filled in the concentrate departments on the hydrolysis degree, hydroxide precipitation formation and mass transfer in the inside of stack. It showed that when the volume ratio (A:C) was7:3, the EDI device could get the best processing results and stability among the inspection time. Comparing with the performances of EDI stack without resin in concentrate departments, the certain volume ratio of anion and cation exchange resin filled in the concentrate departments could adjust the hydrolysis degree and the solution pH of concentrate departments, and achieve the purpose of eliminate hidden trouble scale formation ultimately.4. Study on the long term stability of EDI stack. The EDI stack, equipped with cation exchange resin in dilute departments and a mixed resin bed with a volume ration of7:3(A:C) in concentrate departments, was investigated about17days under normal operation. The experiment showed the EDI device had a good stability, and the product water could meet the standards of heavy-metal wastewater discharging for the feed solution whose Ni2+concentration was50mg·L-1and pH was4.5.This paper indicates that the EDI process would be effective for low-concentration heavy-metal wastewater treatment while choosing right stack structure and operating parameters. Besides, the rational design of resin filling way in concentrate departments of EDI stack can alleviate scaling phenomenon effectively and improve the stability of EDI stack. These studies aim at providing the research references for the treatment of low-concentration heavy-metal wastewater by EDI technology.