| In recent years,nano zero valent iron had been widely used in wastewater treatment due to its large specific surface area and high reactivity.However,it also had the defects of easy agglomeration,oxidation,and instability.In this paper,the method of doping with another metal catalyst copper and loading silica had been used to modify the NZVI.Nano zero valent iron?NZVI?,nano iron-copper bimetallic?Fe/Cu?,and silica supported NZVI?SiO2/NZVI?were synthesized by liquid-phase chemical reduction method.They were characterized by scanning electron microscope?SEM?and X-ray diffraction?XRD?,they were used to treat nitrate wastewater and tetracycline wastewater.The effect of wastewater treatment by the modified NZVI and NZVI was compared.The effect of the dosage,the ratio of the load and the initial concentration of the solution et.al on the wastewater treatment was systematically investigated through batch tests.In addition,the products,mechanisms,and kinetics of the reaction process were also studied.The following conclusions had been drawn:?1?The particles of nano Fe/Cu bimetallics were more dispersed and the specific surface area were larger,and slowed the oxidation.?2?The reactivity of nano Fe/Cu bimetallics was much higher than NZVI.The removal rate of nitrate nitrogen increased with the increase of dosage,and decreased with the increase of initial nitrate nitrogen concentration.When the Cu loading was 5%,the nano Fe/Cu bimetallics had the best removal effect.When the Fe/Cu bimetallics dosage was 1.5 g/L,the Cu loading was 5%,and the nitrate nitrogen initial concentration was 100 mg/L,the removal rate of nitrate nitrogen could reach more than 98%in60 minutes.?3?With the continuous progress of the reaction,the concentration of nitrate nitrogen decreased continuously;nitrite nitrogen was as an intermediate by-product,and the concentration increased firstly and then decreased;the ammonia nitrogen concentration was increased,and 79.4%of the final product was ammonia nitrogen;total nitrogen was decreased firstly and then increased,the final total nitrogen was reduced by 15.5%.The reason for the decrease in total nitrogen may be the production of nitrogen or the conversion of ammonia gas.?4?The reaction of nano Fe/Cu bimetallics with nitrates was a simultaneous process of redox and adsorption.The reaction process was a continuous step-by-step reaction,namely NO3--N?NO2--N?NH4+-N.And the reaction conformed to the first-order reaction kinetics.?1?The particles of SiO2/NZVI were more dispersed and the specific surface area were larger,and slowed the oxidation.?2?The activity of was significantly higher than that of NZVI.The degradation rate of tetracycline increased with the increase of SiO2/NZVI dosage and temperature,decreased with the increase of the initial concentration of tetracycline solution,when SiO2:NZVI=1:2,the degradation rate of tetracycline was best,and the degradation effect was better under acidic and neutral conditions than alkaline conditions.Under the conditions of the dosage of SiO2/NZVI 1.5 g/L,SiO2:NZVI=1:2,the initial concentration of tetracycline solution 100 mg/L,pH=6,and the temperature 25°C,the degradation rate of tetracycline reached about 94%in the 60 min.?3?The reaction product of the NZVI-TCs system were mainly derived from tetracycline defunctionalization.Tetracyclic structure was still existed,only destroyed functional groups on its side chains.During the reaction,tetracycline was firstly adsorbed on the surface of SiO2/NZVI,and then took place oxidation-reduction reaction above its surface active site. |
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