Experimental Study On Nitrate In Groundwater Treated By Novel Ternary Metal Electrode

In recent years,the nitrate content in groundwater has continued to increase,and nitrate pollution has become an urgent problem facing the world.Drinking water with too high nitrate content will damage the human liver,produce methemoglobinemia,etc.,especially for infants.In order to minimize the impact of nitrate on health,technologies such as biological denitrification,chemical/electrocatalytic reduction,ion exchange/reverse osmosis,and electrodialysis have been developed to remove nitrate from groundwater.Among them,electrocatalytic reduction has the advantages of simple operation and low cost.,The equipment installation occupies a small area and other advantages.However,traditional electrochemical methods have problems such as low nitrate removal efficiency,low nitrogen selectivity and short electrode life.Therefore,new electrodes need to be developed to solve the above problems.In this study,the Cu-Bi-Pd cathode was fabricated by electrodeposition method using Ti electrode as matrix.Scanning electron microscope（SEM）,energy dispersive spectrometer（EDS）and X-ray diffractometer（XRD）were used to analyze the microscopic morphology,elemental composition and phase composition of the electrode.Electrochemical tests and nitrate electrochemical reduction experiments were used.The electrocatalytic performance,stability,corrosion resistance and product selection characteristics of the electrode were analyzed;the influencing factors of the nitrate electrochemical reduction and removal experiment were investigated,and the optimal treatment conditions were screened;finally,the new ternary metal electrode was tested.The mechanism of nitrate reduction was analyzed and studied.The main research results are as follows:（1）The electrode preparation conditions were optimized by the single-factor control variable method,and the best preparation conditions were obtained:the electrodeposition time was 50 min,the electrodeposition temperature was 28℃,the current density was 4 m A/cm²,and the three metals in the electrodeposition solution were The mass concentration ratio of Cu:Bi:Pd was90:9:1.（2）The simulated nitrate-contaminated groundwater was treated with the prepared Cu-Bi-Pd electrode as the cathode,and the effects of initial p H,current density,initial concentration,treatment temperature and Cl^-concentration on the nitrate removal efficiency were studied.The optimal treatment conditions are:initial p H=7,current density 12 m A/cm²,treatment temperature25℃,under these conditions,the initial concentration of nitrate nitrogen is 100 mg/L,and the nitrate removal rate after 6 h up to 99.2%,nitrogen selectivity up to 69.4%,and energy consumption of 0.586 k Wh/g NO₃^--N.The lower the initial concentration,the shorter the time for complete removal of nitrate nitrogen.After adding a certain amount of Cl^-,the selectivity of nitrogen gas increased significantly,up to 95.0%,and the optimal amount of Cl^-was 0.25 g/L.（3）The prepared Cu-Bi-Pd electrode was used as the cathode to treat the actual nitrate-containing groundwater,and compared with the simulated groundwater,it was found that the nitrate removal rate and nitrogen selectivity were in the order of ultrapure water under the same current density.Tap water>groundwater.However,with the change of current density,the removal of nitrate varies in different water quality.The removal rate of nitrate in ultrapure water increased with the increase of current,while the removal rate of nitrate in tap water and groundwater increased first and then decreased with the increase of current density.The removal rate of nitrate showed the same law.（4）The mechanism of nitrate removal by the electrode was analyzed by the electrochemical workstation.In the sodium sulfate solution alone,the voltage ranged from 0.1 to-1.5 V,and no obvious electrochemical behavior occurred on the electrode surface.In sodium solution and sodium sulfate plus sodium nitrite solution,an obvious reduction peak appears at-1.4 V,which indicates that the reduction of nitrate is direct and step-by-step,and the reduction reaction of nitrate conforms to pseudo-first order.dynamics.