| The arbitrary discharge of wastewaters containing heavy metal ions has caused serious environmental pollutions. Electrodeionization(EDI) technique combines electrodialysis and ion exchange process to remove the heavy metal ions from the wastewaters. In the technique, the acid and alkali regeneration process has been omitted, and no secondary pollutions appear any more. Electrodeionization will be an important and prospective technique for wastewater treatment and resource reuse.First of all, acrylic acid was grafted onto the polypropylene nonwoven fabric under ultraviolet irradiation(PP-g-AA). Secondly, the static adsorption and desorption characteristics of PP-g-AA were studied by removing the copper and nickel ions from simulated and industrial wastewaters respectively. Finally, the long runing stability of the EDI device packed with both PP-g-AA and cationic exchange resin was investigated based on the judgements of the changes of electric conductivity, pH value, content of copper ions, current of the device and surface morphologies of ion exchange membrane and resins. The effects of polarity reverse and the EDI stack structure on the electric permutation and ion removal were also examined. The microstructure, morphology and properties of the PP, and PP-g-AA fabrics, ion exchange membranes and resins were analyzed with infrared resonance and scanning electron microscopy. The following important conclusions are drawn:(1) PP-g-AA has shown a good adsorption performance for the concentrated copper ion wastewaters with the maximum ion uptake capacity 140.7mg/L at the concentration of 1000mg/L. Similarly, the maximum capacity of PP-g-AA for the real nickel ion wastewater was 140.0 mg/L at the concentration of 1000 mg/L.(2) The copper ions adsorption behaviour of PP-g-AA followed the Lagergren’s pseudo-second order kinetic equation. Isothermal equilibrium adsorption observed the Langmuir isothermal adsorption mechanism with the implication of monolayer adsorption.Although the grafted poly(acrylic acid) might be peeled off from the fabric surface, three-time adsorption-desorption cycle demonstrated the satisfied adsorption capacity and removal rate of PP-g-AA.(3) It is the plate-column structure and the mixed packing with PP-g-AA and cationic exchange resin that improve the copper ion permutation and alleviate precipitation with the evidence of the average removal rate of copper ion higher than 99% for the 300-hour electrodeionisation operation.Similarly, the EDI device packed with both PP-g-AA and cationic exchange resin was implemented to treat the real nickel ion wastewater, although the impurities in the wastewater may interface electrodeionisation process, the result of the successive 100-hour treatment of the simulation nickel ion wastewater was still satisfactory. The average removal rate of the nickel ions kept better than 99% within the total 300-hour operation.(4) During the EDI process, the anion exchange resin/membrane stability was better than that of cation exchange counterparts. In fact, the quaternary ammonium group in the anion exchange resin/membrane may change into tertiary amine group, and the amine group catalyzes water dissolution. Over intensified hydrolysis will damage the stability of the device.(5) EDIR expanded the working area of the dilute chamber and promoted the copper ion removal. The alkaline dilute exit stream implied the stability of the anion exchange membrane/resin during EDIR process. It is the change of the ion migration direction that alleviates water dissolution of the mixed resin interfaces and he quaternary ammonium change, as well as eliminates the gathering of hydroxyl ions, with the stability of the device extended during EDIR process.(6) Two patterns of EDI configurations from the polarity reverse EDI design were run and compared by checking the current efficiency and deposition on the anion exchange membrane surface, the results evidenced that the pattern with two-dilute one-concentrate stack was preferable.The innovation of the thesis consists in the joint treatment of the high concentration metal ions wastewaters with the PP-g-AA adsorption tandem electrodeionisation technique with favorite result of the continuous and stable operation of 300-hour with the removal rates of both copper and nickel ions at the higher than 99%, respectively.The feature of this thesis lies in the long term electrodeionisations of heavy metal ions from the simulated and real industrial wastewaters by packing both PP-g-AA and cation exchange resins in the dilute chamber of EDI device with the meaningful results and conclusions. |
PDF Full Text Request