| The contamination of groundwater by nitrate has been a great threat to the drinking water safety, and it draws great attention by scholars from China and overseas to the study which is to remove nitrate from ground water. At present, there are many researches on the technology of nitrate removal, mainly including Physical-Chemical method, Biological denitrification and Chemical reduction process. Compare with the former two ways, chemical reduction method of zero-valent iron technology has shown several advantages, such as simple operation and fast removal rate, suitable for small-scale, low concentration and distributed drinking water treatment, and therefore gained strong interest as an excellent method for nitrate removal. This method, taking zero-valent iron as reducing agent, removes nitrate under proper reaction conditions. Based on improving the removal efficiency of nitrate, it is critical to reduce by-product ammonium as much as it can by controlling the reaction conditions. To increase the stability and efficiency of modified zero-valent iron and control secondary pollution after reaction is the research emphasis in the field of future study.This paper first introduces preparation of nanometer Fe0/Pd/Cu composite materials through liquid phase reduction method and then systematically explore the influence of reaction factors, oxo-anions and organic matter on nitrate removal realized by nanometer Fe0/Pd/Cu composite materials. On the basis of previous study, a preliminary analysis of products and mechanism of nitrate reduction reaction by nanometer Fe0/Pd/Cu composite materials is given, and the kinetic parameters are calculated. Finally, according to the results of the experiment, look ahead the research trend of nanometer iron composite metals applied in nitrate removal.The paper draws the following conclusions:(1) Mass fraction of metal Pd and Cu affected the distribution of nitrate reduction products and the best mass ratio composition was Fe-6.0%Pd-3.0%Cu. The reaction factors, such as dosage of nanometer Fe0/Pd/Cu, initial concentration of nitrate, initial pH value of solution, reaction temperature, stirring speed and initial dissolved oxygen value of solution, had a certain influence on nitrate removal. When the dosage of nanometer Fe0/Pd/Cu was0.250g, initial nitrate concentration was100mg/L, initial pH value of solution was7.10, reaction temperature was20℃, stirring speed was800rpm and initial dissolved oxygen value of solution was0.42mg/L, the nitrate removal rate can reach around82%. Compared with previous reports of nitrate removal by nanometer iron, it effectively reduced the generation of by-products ammonia and improved the removal rate of nitrogen.(2) Nitrite, nitrate, chlorate and bromate can be competed each other between reduction and adsorption by nanometer Fe0/Pd/Cu because of similar molecular structure. Under the experimental conditions, the reduction rate sequency shows as followed:BrO3->NO2->ClO3->NO3-. Phosphate, sulfate and bicarbonate co-existed can compete with nitrate by seeking adsorption sites on the nanometer Fe0/Pd/Cu surface under the experimental conditions, thus reduce the nitrate removal rate. The stronger relation of affectivity is as followed:HCO3->SO42->PO43-.(3) Nitrate reduction reaction by nanometer Fe0/Pd/Cu carried out on the reductant surface and followed the pseudo-first-order rate kinetics.In this experiment, nanometer Fe0/Pd/Cu particles had larger specific surface area (51.0372m2/g), small particle size (20-80nm) and high activity which can remove nitrate effectively. |
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