Experimental Study On Degradation Of Nitrobenzene Containing Wastewater By Modified Nanoscale Zero-valent Iron

As an important intermediate of organic synthesis,nitrobenzene is extensively used in the fields of national defense,medicine,printing and dyeing.At the same time,nitrobenzene is a priority pollutant in environmental control as a type of virulent chemicals.Nitrobenzene can be treated by physical or chemical methods because of its biological toxicity and resisitence to biological degradation.Since zero-valent iron(ZVI)is cheap and easy to obtain,the technology is also simple,so it is widely used in all kinds of wastewater treatment.A lot of research and engineering practice at home and abroad shows that ZVI can effectively reduce nitrobenzene to aniline.Further,the biodegradability is improved.A lot of studies show that the zero valence iron and nitrobenzene are surface reaction,so the greater the specific surface area of zero valence iron,the faster the reaction rate.On the other hand,high surface free energy and inherent ferromagnetic of the newly prepared nanoscale material make it easy to agglomerate or tend to surface oxidation,resulting in decreased degradation efficiency of nitrobenzene.Furthermore,the surface hydrophilic nature leads to relatively low affinity of NZVI to hydrophobic nitrobenzene.Supporting of NZVI in or on solid substrate is an alternative to solve these problems and to improve the reactivity of NZVI.In this paper,preparation of NZVI was conducted by liquid phase reduction method,and activated carbon fiber(ACF)was used as the carrier for modification of NZVI.The conditions for preparation of ACF loaded NZVI were optimized.The composition and morphology of the composite material were characterized by X ray diffraction(XRD)and scanning electron microscope(SEM).In the study of treatment of nitrobenzene containing wastewater by ACF-NZVI,the effects of parameters,such as initial pH,ACF-NZVI dosage,initial concentrations of nitrobenzene,reaction rate,on the removal efficiency of nitrobenzene were investigated.Removal efficiency of nitrobenzene by iron powder and ACF-NZVI,ACF-NZVI and NZVI,ACF-NZVI and granular active carbon(GAC)supported NZVI were compared.And the mechanism of nitrobenzene removal was also preliminary discussed.The conclusions are as followed:(1)In preparation of ACF-NZVI using liquid phase reduction method,FeSO4·7H2O and KBH4 are ideal reaction reagents.The ratio of ethanol to water in the liquid phase was 5:7(volume)and pH of the reaction was 6.0.The KBH4 should be added at the rate of 0.10mL/s.The ratio of NZVI was 20%(weight)in the composite material.ACF-NZVI prepared under these conditions shows good reaction activity and surface stability.(2)Characterization of NZVI by XRD shows that the NZVI prepared has a microcrystalline structure.SEM of ACF-NZVI reveals that NZVI is well dispersed on the surface of ACF,which effectively reduces the phenomenon of agglomeration of NZVI.(3)The optimal reaction conditions for the treatment of nitrobenzene by ACF-NZVI are: lower pH(about 4),relatively higher ACF-NZVI dosage,initial concentration of nitrobenzene at about 200mg/L and moderate reaction rate(about 200rpm).(4)The removal rate of nitrobenzene in wastewater by ACF-NZVI was 27.4 times as much as that of iron powder.The removal rate of ACF supported NZVI is 1.46 times as much as that of GAC supported NZVI.The removal rate of per gram of ACF supported NZVI is also better than NZVI.ACF absorbs certain amounts of nitrobenzene and aniline,which explains better removing performance of ACF supported NZVI compared to NZVI.(5)Removal of nitrobenzene by ACF-NZVI is mainly accomplished by chemical reduction of NZVI,and ACF can also absorb certain amounts of nitrobenzene.In addition,ACF also,to a certain extent,adsorbs the ending reaction product-aniline,which reduces the competition of aniline to the active sites on the surface of NZVI.