Study On The Performance And Mechanism Of Membrane Electrolysis For The Treatment Of Complex Heavy Metal Ions In Wastewater

In recent years,the rapid development of printed circuit board（PCB）industry increased the use of electroplating process.The Cu²⁺in industrial wastewater often combines with OH^-,Cl^-,SO₄^2-,NH₄⁺,humic acid,organic acid,fulvic acid and amino acid complex agents to form copper complex.The complex can exist stably in a wide p H range and has poor biodegradability,which poses a great threat to human health and environmental safety.Conventional chemical precipitation and other technologies are difficult to treat copper complex wastewater effectively,so it is urgent to develop a novel technology to degrade copper complex wastewater efficiently.In this paper,the membrane electrolysis is proposed to treat the Cu-EDTA wastewater,the oxid-reduction mechanisms as well as its application of membrane electrolysis are investigated.（1）Construction of novel electrochemical reactor.The anode chamber and cathode chamber of the reactor are connected with the peristaltic pump to circulating the electrolyte,and the mass transfer can be controlled by adjusting the speed of the peristaltic pump to reduce the concentration polarization on the electrode surface.The optimum experimental conditions for the treatment of Cu-EDTA simulated wastewater by membrane electrolysis were determined by single factor experiments such as initial p H,the distance between anode and cathode plates,the current intensity and the initial concentration of Cu-EDTA.When the electrolysis system used a Ti/Ru-Ir O₂ anode and a stainless steel plate cathode,the optimal conditions of Cu-EDTA treatment are as follows:the conditions of p H=6.0,current intensity 0.200 A,plate spacing 10.0 mm and initial solubility 5.0 m M.The removal rates of Cu²⁺and TOC are 99.1%and 51.2%,respectively.The optimum conditions of membrane electrolysis system with Si/BDD anode and stainless steel electrode cathode are p H=7.0,current intensity 0.240 A,plate spacing 10.0mm and initial solubility 5.0 m M.After 180 min electrolysis,the removal rates of Cu²⁺and TOC are 99.8%and 92.2%,respectively.（2）Optimization of the experimental conditions for the treatment of Cu-EDTA wastewater by non-diaphragm electrolysis.The results show that the optimal reaction conditions for Cu-EDTA solution with Ti/Ru-Ir O₂ anode and stainless steel plate cathode are as follows:p H=6.0,current intensity 0.32 A,plate spacing 10.0 mm,initial 5.0 m M Cu-EDTA.After 180 min electrolysis,the removal rates of Cu²⁺and TOC are 99.6%and38.9%,respectively.The optimum conditions for the system with Si/BDD anode and stainless steel cathode are:p H=7.0,current intensity 0.320 A,plate spacing 10.0 mm and initial 5.0 m M Cu-EDTA.After 180 min electrolysis,the removal rates of Cu²⁺and TOC were 99.7%and 92.1%,respectively.（3）Comparison of the efficiencies of membrane electrolysis and non-diaphragm electrolysis for the treatment of Cu-EDTA simulated wastewater.The results show that H₂O₂ production in membrane electrolysis with Si/BDD anode is higher than that in non-diaphragm electrolytic system with Si/BDD anode,the generated H₂O₂ concentrations are 7.58 m M and 5.06 m M,respectively.The corresponding^·OH concentration in membrane electrolysis system reaches the highest 11.24μM in 15 min,and^·OH concentration in non-diaphragm electrolytic system reaches the highest 2.72μM in 20min.Compared with electrolytic system,H₂O₂ and^·OH production in non-diaphragm electrolytic system is greatly improved.It indicates that the existence of cation exchange membrane can accelerate the generation of oxidants and improve the oxidation capacity.（4）The conversion of Cu-EDTA treated by membrane electrolysis and non-diaphragm electrolysis was aslo investigated.The results showed that the concentration of formic acid produced in non-diaphragm electrolysis system increased rapidly with the increase of electrolysis time,then remained stable and then decreased rapidly.The maximum concentration was 0.56 m M at 60 min,and it began to decrease after 90 min.In the membrane electrolysis system,the concentration of formic acid increased rapidly with the increase of electrolysis time and then decreased rapidly.It reached the maximum concentration of 0.58 m M at 60 min.It shows that the membrane electrolysis has better efficiency than the electrolysis system.（5）The influence of coexistence of inorganic ions and organic compounds in the membrane electrolysis system on the treatment of Cu-EDTA simulated wastewater was further explored.The results showed that inorganic ions could affect the mineralization,but had little effect on the removal rate of Cu²⁺ions.The presence of Cl^-,NO₃^-and PO₄^3-is not conducive to the mineralization of Cu-EDTA in the membrane electrolytic system,and the mineralization rate decreases from 92.1%to 72.1%,75.6%and 59.1%after 180min electrolysis,respectively.The inhibition of PO₄^3-was more obvious.The presence of HA and other organic compounds has little effect on Cu²⁺removal,but is not conducive to the mineralization,in which TOC removal decreases from 92.1%to 34.6%.