Reserch Of Electrochemical Oxidation Of Nitrogen Wastewater By Bi-doped PbO₂Electrode

Bi-doped PbO2and pure PbO2electrodes were prepared by electrodeposition basedon Ti substrate and were characterized by scanning electron microscopy (SEM), X-raydiffraction (XRD), X-ray photoelectron spectroscopy (XPS) and cyclicvoltammetry.The results showed that the surface structure of PbO2electrode wasimproved by doping bismuth, which made the crystal unclear size and active layersurface of PbO2electrode more smaller and compact leaded to form a larger responsesurface.The prepared electrodes were selected as electrodes for electro-oxidationdegradation of ammonia nitrogen in simulated wastewater were systematicallyinvestigated. It indicated that the Bi-doped PbO2electrode had excellentmicrostructure as well as excellent electrochemical properties than pure PbO2electrode. The removal efficiency of ammonia nitrogen was improved with increasingcurrent density and the effect was better on the condition of alkaline than acid.Moreover, an appropriate concentration of chloride ion could benefit to removal ofammonia nitrogen under the condition of alkaline. The removal efficiency ofammonia nitrogen could reach up to100%after electrolysis for120minutes at initialconcentration of ammonia nitrogen was50mg/L, the current density was40mA/cm2,pH was12and chloride ion concentration was600mg/L. The electrochemicaloxidation of ammonia nitrogen was removed through indirect oxidation under acidiccondition and direct electro oxidation jointly with indirect oxidation under alkalinecondition when chloride ion was absented, and mainly through indirect oxidation byactive chlorine generated in the solution when chloride ion was present.Through the research on ammonia nitrogen simulated wastewater,the experimentfurther studied the electrochemical oxidation of ammonia nitrogen and COD inlandfill leachate and the degradation mechanism by Bi-PbO2electrode.The resultsshowed that in the condition under the current density of50mA/cm2,initial pH of7,initial chloride ion concentration of6000mg/L, electrolytic time of4hours whichthe ammonia nitrogen and COD removal rate was99.6%and89.3%,respectively.Electrochemical degradation of ammonia nitrogen in landfillleachate matched with first order kinetics equation.The degradation mechanism oflandfill leachate including two parts which were small molecule organic matterremoved mainly by hydroxyl radical and active chlorine finally into CO2,meanwhile the macromolecular organic matter was mainly oxidated into intermediate by thePbO(OH)2generated on the surface of Bi-PbO2electrode.