Effects Of Electrode Modification On The Treatment Of Electroplating Wastewater Through Electrocoagulation

Development of electroplating industry was considerably rapid in recent years,leading to the continuously increasing electroplating sewage discharge.Therefore,the large amount of highly polluting heavy metals produced within this type of wastewater also cannot be underestimated.Traditionally,chemical methods not only need to add a large number of chemical agents,but could barely dispose the actual electroplating wastewater containing complexes of zinc–nickel.Herebythe option of electrocoagulation（EC）technology for the substantial treatment of actual electroplating wastewater might be promising.Focused on the increasing cost due to frequent replacement of anode during EC operation,SS-PPy modified anode was prepared by employing polypyrrole（PPy）modification coating,which provides unique electrochemical characteristic and environmental friendliness.In addition,the removal effect,the corrosion inhibition efficiency of anode and the treatment process of EC were explored.Moreover,it was also found that PPy modified anode could effectively protect the anode and prolog its service lifespan during EC process.The main conclusions of this study are as follows:（1）Different characterization techniques and electrochemical behavior of the four types of PPy coatings were compared and evaluated.SEM,EDX and FT-IR,jointly confirmed that electrodeposition method could allow the successful polymerization of polypyrrole/dopants on430 stainless steel plates to form a complete PPy coating.Moreover,the PPy/PTS（Polypyrrole/P-toluenesulfonate）coating showed the most dense and flat surface layer with a low roughness of only 69 nm,indicating that it was extremely difficult to be eroded by corrosive media.In addition,OCP,EIS,Tafel and immersion test results demonstrated that PPy/PTS achieved the best electrochemical corrosion performance,and could provide the best defending effectiveness for electrode,as its R_pvalue reached 1834.28Ω/cm²,and corrosion current density was low at 9.09μA/cm².（2）Removal effect by PPy modified anode and bare steel anode under different operating parameters of EC was compared.Taking into account the treatment efficiency and economic cost,the optimum conditions for EC were as follows:the plate spacing was 20 mm,initial p H was 4,reaction time was 70 min,and the current density was 30 m A/cm².During multi-batch EC processing,the PPy modified anode provided expected treatment stability,which could be consistent with the removal level of bare steel anode.Besides,removal efficiency of Zn²⁺and Ni²⁺could be stable at 99.99%and 80%.（3）The corrosion inhibition efficiency of PPy modified anode was evaluated by weight loss method.It was found that the corrosion inhibition efficiency of the anode was relatively higher when the wastewater was strongly acidic.With the increase of time and current density,the corrosion inhibition efficiency of the anode would gradually decrease.In addition,the corrosion inhibition efficiency of anode during multi-batch EC processing could be stabilized at 30%.Besides,SEM images after EC reaction also showed that the surface of PPy anode was smoother,whereas the corrosion damage was much lighter than that of bare steel anode.It was proved that this modified anode material could protect the anode during EC reaction by ensuring a great removal effect of heavy metals,and to effectively prolong the service life of the anode.（4）During the process of EC,the energy consumption of the PPy modified anode was relatively consistent with that of the bare steel anode.With the increase of current density and the prolonging of electrode operation,the Fe utilization rate of anode decreased gradually.Moreover,the Fe utilization rate of PPy modified anode was significantly higher than that of the bare steel anode.Importatnly,the COMPASSⅡforce field in Materials Studio was applied to carry out molecular simulation,it was found that adsorption energy between PPy/PTS and metal surface was the lowest as-88.87 k J/mol.Therefore,the PPy/PTS coating displayed the strongest binding ability with metal surface,and further proved that this coating could provide the best corrosion inhibition and protection performance.