Ammonia Treatment By The PbO₂Powder Porous Electrode And Its Application In The Nitrate Removal

In this thesis,ammonia nitrogen treatment by the PbO₂powder porouselectrode which was homemade and its application in the nitrate removal werestudied.The lead dioxide powder porous electrode, modified by graphite andactivated carbon powder added in the homemade β-PbO₂powder, was prepared byhigh pressure molding. The electrochemical properties of the electrode werecharacterized by X-ray diffraction （XRD）, scanning eleetron microscopy （SEM）and cyclic voltammetry curves. The results showed that the PbO₂crystal could bedistributed uniformly. The effective area and catalytic activity of the electrodewere improved by mixed powder added.The lead dioxide powder porous electrode was used as anode, and thestainlesssteel as cathode to treat ammonia wastewater. The effects of quantity ofmixed powders, current density, initial pH and chloride ion concentration on theelectrocatalytic oxidation were studied. The results showed that the treatment effectwas better when the mass percentage of graphite and activated carbon powderadded was15%to20%. The removal efficiency of ammonia nitrogen increasedwith the increasing current density and was higher under alkaline conditions. At thesame time, the electrochemical oxidation rate could be improved significantly bychlorination ion added and so the oxidation time was shorten greatly. The productof ammonia oxidation was NOx gas but mainly N2and a small amount of nitratenitrogen.On the basis of the above experiment, the treatment of nitrate by the leaddioxide powder porous electrode which was used as anode was studied. Thestainless steel was used as cathode to reduce nitrate nitrogen, and the effects of thecurrent density, initial pH, catalytic time, chloride ions and initial ammoniaconcentration on the nitrate removal was studied.Simultaneously, the divided cellswas used as a reference to explore the mutual influence of the cathodic reduction ofnitrate nitrogen and the anodic oxidation of reduction product （ammonia）.Theresults showed that cathodic reduction products of nitrate nitrogen in the dividedcells were mainly ammonia and a small amount of nitrite nitrogen, and thereduction efficiency and proportion of ammonia generated were relatively largerunder high current densitiy or weakly acidic conditions. The reduction of nitratenitrogen would be hindered when the initial concentration ratio between ammonia and nitrate nitrogen increased to1:1. In the undivided cells, the anode couldremove ammonia effectively which was produced by the reduction of nitratenitrogen, and inhibit the generation of nitrite. The oxidation-reduction efficiency ofthe whole reaction system increased with the increasing current density, and theconcentration of nitrate nitrogen was decreased gradually with increasing of thereaction time, especially under weekly acidic conditions. Though ammonia removalefficiency could be improved by chlorine ion added, nitrate removal efficiencyenhanced little. The oxidation of ammonia nitrogen could eliminate its impact onthe reduction of nitrate nitrogen.