Application Study On Electro-activated Persulfate System For Enhanced Treatment Of Complex Copper From Printed Circuit Boards Wastewater

Printed Circuit board（PCB）is essential and basic component in the electronic industry.It is used as the supporting body of components in various electronic devices.The increasing number of electronic equipment promotes the development of printed circuit board industry,which produces a large amount of printed circuit board wastewater.The printed circuit board wastewater contains complex copper waste-water,which is usually pretreated by adding a collateral-breaking agent first and then adding a flocculant to precipitate.The treated wastewater will enter the subsequent treatment facilities.There are some problems in this process,such as copper can not be recovered effectively and sludge containing heavy metals can be disposed.In this study,Boron-doped Diamond（BDD）electrode was used as anode and stainless steel as cathode to construct electro-activated persulfate system with Cu-EDTA complex in complex copper wastewater as the target pollutant,aiming to achieve simultaneous decomplexation and electrodeposition of Cu-EDTA complex.The degradation efficiency and the mechanism of electro-activated persulfate removal by BDD electrode were analyzed.In the electro-activated persulfate system with BDD,the effects of different concentration of sodium persulfate（PDS）,initial p H of solution,current density and electrode spacing on the reaction system were analyzed by single influencing factor experiments,and the optimal reaction conditions were obtained.The optimum reaction conditions were as follows:initial p H of the solution was 3,PDS concentration was 6 mmol/L,current density was 10 m A/cm²,and electrode distance was 3 cm.Under the optimal reaction conditions,the removal rate of Cu-EDTA and Cu²⁺reached 99.93%and 82.74%at 3 h,and the removal rate of Cu²⁺reached 92.62%at 4 h.Using methanol and tert-butyl alcohol as active species trapping agents,free radical trapping experiments were carried out in the system of Cu-EDTA complex removal by electroactivation of persulfate with BDD electrode.The results showed that·OH existed in the reaction system,and other active species and non-free radical oxidation process of activated persulfate might exist.The kinetic constants of the first order reaction were calculated to verify the results.The active species in the reaction system were detected by electron spin resonance（ESR）,and the existence of·OH and non-radical oxidation process in the reaction system was confirmed.The mechanism of electroactivation of persulfate on BDD electrode was analyzed by linear sweep curve and chronocurrent curve.The degradation and removal of Cu-EDTA complex in the reaction system was attributed to the generation of·OH by electrolysis of water on BDD electrode,the non-free radical oxidation process of activated PDS and the electron transfer process on the electrode surface.Meanwhile,the activation of PDS promoted the generation of·OH.The copper ion did not activate the persulfate,but it did act as a catalyst.The intermediate products of Cu-EDTA degradation were analyzed by high performance liquid chromatography-time-of-flight mass spectrometry（HPLC-QTOF-MS）.It was found that other Cu-EDTA complexes formed in the degradation process of Cu-EDTA complex,and then the complexation and electrodeposition process were realized in the oxidation process,resulting in Cu²⁺was not immediately released into the solution.Therefore,the electrodeposition effect of Cu²⁺is affected.The first-order reaction kinetics equation and second-order reaction kinetics equation were used to fit the data of Cu-EDTA complex removal by anodic degradation under different influencing factors,and it was found that the degradation and removal of Cu-EDTA complex was a first-order reaction.The reduction potential of the stainless steel electrode to PDS and Cu-EDTA is the same,and there may be competition in the reaction system where the two coexist.Through further analysis of the chronocurrent curve,it is concluded that the electrodeposition of Cu-EDTA complex copper and the electrodeposition of decomplexing free copper ions is mainly carried out in the cathode,and there is no cathode activation persulfate process.Through XRD analysis of electroplating coating,it is found that the product of electrodeposition process is elemental copper.The relationship between the current efficiency of cathodic reduction of copper and the energy consumption in the reaction process and the current density was analyzed,and the current density of 10 m A/cm² was determined to be the appropriate current density.The anode and cathode have good stability through 20cycle electrolytic experiments with the same electrode.In this study,the construction of electro-activated persulfate system with BDD electrode provides a theoretical basis for the analysis of the treatment of metal complex complexes with BDD anode electro-activated persulfate,and provides a new treatment technology for the treatment of copper complex wastewater with printed circuit board.