A Novel Technique Of Heavy Metals And COD Removal From Electroplating Wastewater By Fenton-alternating Current Coagulation

With the rapid development of Chinese electroplating industry,the number of electroplating factories has drastically increased.At present,the problem of electroplating pollution has brought extensive attention from the environmental protection organizations.Traditional wastewater treatment methods include biological treatment,chemical sedimentation,adsorption,Fenton oxidation,and membrane exchange technology,but these methods have the disadvantage of high cost,low removal efficiency,secondary pollution,and high energy consumption.Fenton-sinusoidal alternating current flocculation（FSACEC）is the emerging and new technology that combines oxidation·OH with iron electrode sinusoidal alternating current electrocoagulation to treat heavy metal ions and organics efficiently in electroplating wastewater.In this thesis,the removal of Ni²⁺-complexes and chemical oxygen demand（COD）from simulated electroplating wastewater by FSACEC technology are studied.The effects of parameters such as current concentration（I_V）,initial p H（p H₀）,the addition of H₂O₂,voltage（V）,and initial concentration on the removal of COD and nickel ions were investigated through batch experiments.In addition,SEM,FTIR,EDS,XRD analysis was performed on FSCEC coagulations to better understand the removal mechanism.The results of COD removal by FSACEC process showed that the COD removal efficiency increased with the increase of the current concentration.When the p H value of the wastewater was 2.0,the COD removal efficiency reached the maximum.In p H₀2.0 wastewater,applying current concentration of 1 A·dm^-3,the addition of 20cm³·dm^-3 30%H₂O₂,the removal efficiency of COD reached 94.21%and the residual COD in wastewater was only 60 mg·dm^-3 after 90 min run.The FSACEC process is in accordance with the kinetic law of the pseudo-second-order kinetic adsorption model for COD removal.The removal rate of nickel complexes increased with the increase of the current concentration by FSACEC.The removal rate of nickel ion complexes reached the maximum at p H 2.0.The optimal operating parameters are.The removal rate of the nickel ion complex reaches 98.972%,and the residual amount is 1.03 mg·dm^-3 through30 minutes FSACEC by 1 A·dm^-3,adding 20 cm³·dm^-3 30%H₂O₂.Scanning electron microscopy（SEM）analysis showed that the particle diameter of the COD coagulations produced by FSACEC was between 30 and 40 nm,which was smaller than the particle size of Fenton-DC electrocoagulation.FSACEC coagulations are a nano-scale particle with a large specific surface area so as to easily adsorb organic complexes.Compared with the single Fenton technology,the FSCEC process has higher COD removal efficiency and a higher p H₀ operating range.The FSACEC process conforms to the kinetic law of a quasi-second-order kinetic adsorption model.SEM analysis demonstrates that the particle size of coagulations containing nickel complexes formed by FSECEC was 231 nm,but about 35nm for coagulations containing organics.EDS analysis shows that there is nickel component in the flocculants,which is composed of nickel complex ion,nickel hydroxide,and the complex substance formed with the iron hydroxide.The mechanism of removal nickel ions includes the two processes of co-precipitation and surface adsorption.Simulation of actual wastewater was designed.The residual of Cr³⁺,Cu²⁺,Ni²⁺,and COD in the effluent after FSECEC treatment were 0.213,0.564,0.246 mg·dm^-3,and 30 mg·dm^-3,respectively.It strongly shows that the discharge meets the national emission standards and FSECEC process is effective for the treatment of chemical plating wastewater without the venture of secondary environmental pollution.