| The nickel ions in the electroplating wastewater easily form a nickel complex with the organic complexing agent,which is highly toxic,has poor biodegradability,and can exist stably for a long time.For complex nickel wastewater,it is difficult to remove it effectively by conventional water treatment techniques such as adsorption and alkali precipitation.In this paper,Fenton-Ozone oxidation and electrooxidation are used to remove complex nickel from water.An experiment of the treatment of Ni（II）-citrate wastewater by Fenton-ozone two-stage oxidation technology was designed.The results show that for the Ni（II）-citrate simulated wastewater with a nickel content of 50 mg/L,under optimized conditions:the initial p H of the Fenton stage was 5.0,the dosage of H2O2 was 0.15 m L/L,and the dosage of Fe2+was111.11 mg/L,after 12 minutes of reaction,the effluent directly enters the second ozone stage,and the ozone concentration was fixed at 30 mg/L for18 minutes,so that the removal ratio of nickel citrate can reach more than99.8%.The simultaneous electro-oxidation of Ni（II）-citrate and electrodeposition recovery of nickel metal were attempted in a combined electro-oxidation-electrodeposition reactor with a boron-doped diamond（BDD）anode and a polished titanium cathode.Effects of initial nickel citrate concentration,current density,initial p H,electrode spacing,electrolyte type,and initial electrolyte dosage on the removal efficiency and nickel recovery were investigated.The efficiencies of Ni（II）-citrate removal and nickel metal recovery were determined to be 100%and over72%,respectively,under the optimized conditions（10 m A/cm2,p H 4.09,80 m M Na2SO4,initial Ni（II）-citrate concentration of 75 mg/L,electrode spacing of 1 cm,and 180 min of electrolysis）.The energy cost for Ni（II）-citrate removal was only 0.031 k Wh/L and the removal efficiency of TOC by electrochemical system process is as high as 73.7%at the current density of 10 m A/cm2.Ni（II）-citrate complexes were degraded by electro-oxidation,generating Ni2+and small-molecule oxidized products.The deposits at the cathode were characterized by SEM,EDS,XRD,and XPS,and the analysis results show that metallic nickel and Ni（OH）2 co-deposited at the cathode,and the purity of metallic nickel was more than 95%.Electrodes,including ceramic/α-Pb O2,ceramic/α-Pb O2/β-Pb O2,and ceramic/α-Pb O2/β-Pb O2-PTFE,have been prepared by chemical deposition-electrodeposition methods.The surface morphology and crystal structure of the prepared electrodes were analyzed by SEM and XRD.The analysis results show that three kinds of ceramic-based lead dioxide electrodes have been successfully prepared,and the surface morphology of the ceramic-based lead dioxide electrode modified by PTFE has been improved and the stability of the electrode has been enhanced.The electrochemical performance of the lead dioxide electrode was tested with LSV curve,CV curve,accelerated life of the electrode,and ability to produce hydroxyl radicals.The test results show that the electrode modified by PTFE has a higher oxygen evolution potential,electrocatalysis and long service life.The simultaneous decomplexation of Ni-EDTA and electrodeposition recovery of nickel metal were attempted in a combined electrooxidation-electrodeposition reactor with these three Pb O2 electrodes and polished titanium cathode.Effects of initial Ni-EDTA concentration,current density,initial p H,and initial electrolyte dosage on the Ni-EDTA removal efficiency and nickel recovery were examined.The results show that the removal efficiencies of Ni-EDTA and the recovery ratios Ni element were determined to be 96.2%and over 43.1%,respectively,under the following experimental conditions:current density of 30 m A/cm2,p H7,100 m M Na2SO4,initial Ni-EDTA concentration of 100 mg/L,and 180min of electrolysis. |
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