Research On The Removal Of Nitrobenzene And Cr(?)-containing Wastewater By Loaded Nanoscale Zero Valent Iron

The Nano-sized zero-valent iron(NZVI)reduction technology is a promising technology in remediation of environment pollution.The NZVI has been widely used to remediate environment pollution,due to its small particle size,large special surface area and high surface reactivity.However,there are two major disadvantages about the NZVI that lead to limit its application in the treatment of wastewater.The first is that the NZVI is prone to agglomerate,leading to some electrons of NZVI hard to be used;the second is that the NZVI is easily oxidized by O2 and H2O as exposing to air or water,resulting in the waste of electrons.How to solve the two problems?Reaserchers suggest lolding the NZVI,which has been provento be an Efficiency method.In recent years,active carbon,carbon fiber,graphene or graphene oxide,montmorillonite and mesoporous materials have been widely used to support NZVI.However,a lot of them are powder loding materials,which is difficult to be recycle-d.In this study,we prepared Fe@Al2O3 composites using wetness impregnation and sodium borohydride reduction synthesis pathway with 3-5mm alumina ball as a support material of NZVI.Fe@Al2O3 composites exhibit good stability and persistent reducibility.It was characterized by X-ray diffraction(XRD),scanning electron microscope(SEM),and N2 adsorption/desorption.Furthermore,the Fe@Al2O3 composites was used to remove the wastewater of Cr(?)and nitrobenzene(NB).In the study of removal of Cr(?),the effects of the electron efficiency,reaction concentration and reaction conditions of Fe@Al2O3 reduction Cr(?)on the electronic efficiency were investigated.In the study of removal of NB,the effect of initial concentration of NB and dosage of Fe@Al2O3 on activity were investigated.,and by GC-MS examined the nitrobenzene degradation byproducts,analyzes the mechanism of the degradation of nitrobenzene.Results were as follows:(1)Fe@Al2O3 composites can effectively improve the agglomeration of NZVI and enhance the stability of ZVI.The NZVI particles in Fe@Al2O3 composites are dispersed uniformly on the Al2O3 carrier,and the particle size is small.The surface area and pore volume of Fe@Al2O3 composites were decreased,compared to Al2O3,but the structure characteristics of the carrier were still maintained.In oxidizing environment(O2/H2O),Fe@Al2O3 can maintain a longer activity,which is due to the fact that Al2O3 carrier can prevent the O2/H2O contact with nano-iron,and avoid the side reaction between ZVI and O2/H2O.(2)Research on the reduction of Cr(?)by Fe@Al2O3 composites.We investigated the activity and electron efficiency(EE)of Cr(?)reducing by Fe@Al2O3 composites.Results showed that the total amount of Fe@Al2O3 was 1.0 g/L,pH 6.8,Cr(?)concentration was 5 mg/L,and the total amount of NZVI and Fe@Al2O3 reduction was 0.21 mg and 0.27 mg respectively.Fe@Al2O3 has more total removal of Cr(?)due to the better stability and more durable reduction of Fe@Al2O3.It was found that the electron efficiency of Fe@Al2O3 composites was 1.52 times than that of the unloaded nano-iron powder.The EE was significantly improved.The effect factors of Cr(?)reduing by Fe@Al2O3 composites are pollutants concentration,atmosphere gas(N2)and carrier types and so on.The results show that the pollutant concentration is higher,the the EE of Cr(?)reducing by Fe@Al2O3 composites is higher.Under N2 condition,the EE of Fe@Al2O3 reduing Cr(?)is 2.22 times than that of air.It is indicated that the electron efficiency of Cr(?)reducing by Fe@Al2O3 composites will be higher in the environment with low oxygen concentration and high Cr(?)concentration,and the cost will be lower.(3)Research on degradation of nitrobenzene by Fe@Al2O3.The activity of Fe@Al2O3 degradation of nitrobenzene was investigated.The results showed that NZVI was injected with 1.0 g/L and the initial concentration of nitrobenzene was 23.5 mg/L,and the removal rate of nitrobenzene in the Fe@Al2O3 and unloaded NZVI was 95.39%and 100%in 24 h and 52 h respectively.NZVI dosing quantity of 1.0 g/L,initial conceIntration of 23.5 mg/L,nitrobenzene within 500 h,Fe@Al2O3 the amount of nitrobenzene(1.8 mg)removal is unloaded NZVI(0.85 mg)of 2.12 times,it can be seen that Fe@Al2O3 of nitrobenzene removal rate is lower than in the short run without load NZVI,but in the long term the removal of nitrobenzene amount by Fe@Al2O3 was more.Therefore,Fe@Al2O3 can be applied to the treatment of nitrobenzene wastewater requiring longer repair cycles.Fe@Al2O3,after reaction with nitrobenzene detected solution of intermediate in aniline,nitrobenzene,oxidation azobenzene,azobenzene,neighbouring nitrophenol,N-formyl aniline,nitro diphenylamine and inorganic nitrogen.Fe@Al2O3 reacts with O2 and H+ to form two significant substances---Fe2+ and H2O2,a small number of Fe2+ combined with H2O2 generated hydroxyl radicals(·OH),intermediate generated a small amount of oxidation,the oxidation products of NO2--N and NO3--N.Fe@Al2O3 direct reduction nitrobenzene and-OH oxidation degradation nitrobenzene are the main reaction mechanism of the system.To sum up,Fe@Al2O3 for stability is strong,can be used to repair the low oxygen concentrations of wastewater containing chromium,and repair of nitrobenzene wastewater has more lasting activity.It can be used in the long-term restoration of nitrobenzene wastewater,more economical.