Electrochemical Removal Of Ammonia In Coking Wastewater

The production capacity of coking industry is developing. It brings notonly the development of national economy, but also the environmentalpollution. There are a lot of pollutants in coking wastewater. The content ofCOD and ammonia are 1000～3000mg/L and above 200mg/L respectively.The popular method of treating wastewater is biological method, whichneeds large area and strict purification section. Phenol and cyanogens canreach the national standard by common biological treatment. But the ammoniawhich is the substance causing water eutrophication and environmentalpollution can't reach the national standard. Its removal is the main problem inpresent wastewater treatment. The electrochemical technology only needsroom temperature and pressure and it's easy to be controlled. The effects ofeach factor in removing ammonia in coking wastewater and theelectro-catalytic oxidation mechanism of ammonia were studied on Ti/SnO₂+Sb₂O₄/PbO₂ anode. The estimation of electric energy and research ofmechanism were systematically studied to electrochemical removal of ammonia in coking wastewater first. It provides a new method to treatammonia in coking wastewater.The Ti/SnO₂+Sb₂O₄/PbO₂ anode was prepared by the combinationtechnology of thermal decomposition and electrodeposition. A titanium platewas used as a substrate, the intermediate layer and the active layer areSnO₂+Sb₂O₄ and PbO₂ respectively. The anode surface appearance, structurephase and composition valent state were characterized by means of SEM,XRD and XPS. The life and electrochemical catalysis property of the anodewere inspected by fast life test and cyclic voltammetrys respectively. Thenanometer crystal grains on the surface of intermediate layer SnO₂+Sb₂O₄ areuniform and combine tightly each other. The surface of active layer PbO₂which can form good solid-solution with intermediate layer is the tetragonalphase structure and large roughness. So it is beneficial for increasing theexpecting life and electrochemical performance of the anode. And theexpecting life of Ti/SnO₂+Sb₂O₄/PbO₂ is 15.67y.The effect of the current density,the concentration of supportingelectrolyte,anode materials and the pH value to electrochemical oxidativeprocess was studied by orthogonal array experimental design. And theinfluence of each factor was: anode material＞current density＞concentrationof supporting electrolyte＞pH value. The NO_x^- substance didn't be detectedthrough ion chromatogragh. So the results proved that the ammonia hadchanged to nitrogen totally. Ti/SnO₂+Sb₂O₄/PbO₂ was used to treat coking wastewater containing 250mg/L ammonia at 0.05A/cm². After 1 hour ammoniawere removed totally. The current efficiency was 80.9% and the electricenergy was 43.28kwh/kgNH₃-N in this process.The linearity scanning voltammetry curve at different scanning rate isanalysised through cyclic voltammetry. And the electrode process was theirreversible process. The electrochemical oxidation mechanism was discussedand the control step is Cl₂+H₂O→HOCl+H⁺+Cl^-. The electrochemicaloxidative mechanism of ammonia can supply theoretical foundation to realizeindustrialization.