Research On Chemical Denitrification Technology

With the improvement of industrialization and agriculture,Nitrate contamination of water resource can not be ignored.In this paper,the catalytic hydrogenation reduction method is regarded as the most effective,economical and friendly nitrate treatment technology by comparing several technologies of nitrate treatment.This article focuses on the effect of the preparation of Pd-Cu/AC and Pd-Cu/?-Al2O3 catalysts and the reaction conditions on catalytic hydrogenation nitrate reduction.The technology is applied to the removal of nitrate in actual wastewater,investigate the effect of actual wastewater quality on nitrate reduction.The main conclusions are:(1)Activated carbon powder is used as the carrier,Pd is used as the main catalyst,and the loading is fixed at 5%.The catalytic performance of the catalyst changes with the changes of the type of the promoted metal and the mass ratio of bimetal.The optimal 5%Pd-1.25%Cu/AC catalyst is screened for catalytic hydrogenation nitrate reduction,and all nitrate is completely removed when the reaction time is 60 minute.(2)Optimize the reaction conditions of catalytic hydrogenation nitrate reduction with the 5%Pd-1.25%Cu/AC catalyst.Discuss the effect of initial NO3-concentration,catalyst dosage,the pH value of solution and hydrogen flow rate on the reaction.Finally,when the initial NO3-concentration is 100 mg·L-1,the catalyst dosage is 1 g·L-1,the pH value of solution is 5.5,hydrogen flow rate is 100 ml ·min-1 and reaction time is 60 minute,the removal rate of total nitrogen is 73.2%.(3)Catalytic hydrogenation nitrate reduction reaction with the Pd-Cu/AC catalyst is in accordance with the Langmuir-Hinshelwood first-order kinetics model.At room temperature,the adsorption equilibrium constant Kads of NO3-on the surface of the catalyst is 1.19×10-3 L·mg-1,and the apparent reaction rate constant kapp is 3 5.18 mg(L·g·min)-1.(4)Prepare the Pd-Cu/?-Al2O3 catalyst with ?-Al2O3 pellets as carrier,and the catalyst is used for catalytic hydrogenation nitrate reduction reaction.The effect of catalyst preparation conditions on the catalytic activity and selectivity of the reaction is investigated.It is found that the the catalytic performance of the reaction vary with the order of impregnation,bimetallic ratio and metal loading.Finally,when the capacity of Pd is 0.2%,the ratio of bimetallic Pd and Cu is 4:1 and the reaction time is 120 min,the removal rate of nitrate is 98.7%and the removal rate of total nitrogen is 94.4%.(5)The Pd-Cu/AC and Pd-Cu/?-Al2O3 catalysts are characterized by BET?ICP?SEM?TEM?XPS.The results indicate that the active metal Pd and Cu particles are relatively small and disperse uniformly in the surface of carrier.After recycling the used catalyst and reusing it,it is found that the catalytic performance of the catalyst hardly changes,indicating that both catalysts have good stability.(6)The two catalysts are respectively used for the removal of nitrate in the actual wastewater with low concentration.The results show that the activity and selectivity of catalytic reduction of nitrate that in actual wastewater are significantly lower than that in NaNO3 solution with the same concentration of NO3-.Moreover,the Pd-Cu/?-Al2O3 catalyst show better catalytic selectivity.Explore the impact of impurities in the actual wastewater and the common anions and cations on the nitrate reduction reaction,the results show that impurities will reduce the catalytic performance of the catalyst.Cl-and SO42-in common anions do not affect the removal of nitrate,while the presence of HCO3 inhibits the reaction and reduces the catalytic activity and selectivity.The order of the influence of common cations on nitrate reduction rate can be expressed as:K+<Na+<Ca2+<Mg2+<Al3+.