The Study Of Treatment Of Ni-EDTA Containing Wastewater With Electrocoagulation Using The Iron Scrap Packed-bed Anode

EDTA?Ethylenediaminetetraacetic acid?is a common organic complexing agent in electroplating and printed circuit board?PCB?industry,and it is easy to bind with the Ni?II?to form stable Ni-EDTA complex.Ni-EDTA complex is toxic and difficult to degrade by microorganism,which make it exist stablily in a quite long time in the environment.At present,conventional chemical precipitation technology is difficult to remove the Ni-EDTA completely,leading to Ni?II?concentration can not meet the water quilty standards.Hence,it need to explore an economical and practical Ni-EDTA treatment technology.Based on the extensive sources and high surface area of ion scrap and synergy effect of redox,coagulation and adsorption etc.,in the electrocoagulation?EC?,the study proposed that EC used the iron scrap packed PVC as anode and cylindrical graphite as cathode to treat synthesize Ni-EDTA containing wastewater.Firstly,the bath experiments were conducted for optimizing technological paramaters.Meanwhile,the reaction properties and removal mechanism of Ni-EDTA by EC were analysised and explored.Finally,the effect of the removal of Ni-EDTA by co-existing anions were studied.The results of bath experiments indicated that the air-aeration mode was better than the N₂-aeration mode in the Ni-EDTA removal.Removal efficiency of TOC and Ni were increased with the increase of the applied current and reaction time,but the energy consumption in the system was also increased accordingly.On the other hand,it found that the more generation of Fe?O?,the better adsorption on the flocs for Ni-EDTA under the different temperature and pH.The optimal parameters of the EC system using iron scrap packed anode for treatment of 0.017 mM/L Ni-EDTA containing wastewater were obtained with current of 0.5 A,air-aeration rate of 0.2 L/min,temperature of 313 K,packed anode density of 400 kg/m³ and pH of 3.The optimal removal efficiency of TOC and Ni were 95.79% and 94.30%,respectively,and the specific energy consumption?SECS?was 2.70×10^-5kWh/mg?TOC?accordingly.Finally,the system were tested with the real Ni-chelated containing wastewater and great results were obtained under the optimized conditions.In addition,the better removal for pollutants in the electrocoaglator than in the commercial one.The SEM image of iron scrap indicated that electrolyte?Cl^-?had pitting and corrosion during the EC process and it can increase the specific surface area and prevent the passivation of anode.Sludge of EC had a large settling velocity.Sludge volume?SV?and sludge volume index?SVI?were 17.3% and 41.09 ml/g,respectively.The XRD analysis of flocs suggested that precipitation contained ?-Fe₂O₃ The FTIR pattern of flocs indicated that the EDTA was removed by the flocs adsorption.In addition,it found that Fe???can replace the Ni???from Ni-EDTA and released the Ni into solution.Finally,the possible Ni-EDTA removal synergy mechanism of adsorption,co-precipitation,trans-complexing,decomplexing and oxidation were proposed.The effect to differnet anions existed in solution on the removal of Ni-EDTA were also studied.In constrast to SO₄^2-,other three anions had different effect on the Ni-EDTA removal when the anions concentration was 5 and 10 mg/L.The order of influence was: F^-> PO₄^3-> NO₃^-> SO₄^2-.When the anions concentration was 20 mg/L,the order of influence of different anions were PO₄^3-> F-> NO₃^-> SO₄^2-.