Study On The Recycling Of Nano-Fe From Rolled Oil Sludge And Its Catalytic Reduction Of 4-NP Application

With the development of steel industry in China,the treatment of hazardous waste rolling sludge has become a urgent problem to be solved.It will not only cause serious pollution to the environment but also waste resources if not properly disposed.At present,the world is short of water resources.Due to its unique physical and chemical properties,the water pollution caused by p-nitrophenol also becomes an urgent problem to be solved.The purpose of this topic is to separate and reuse nano-iron in rolling sludge,one of the hazardous wastes,through catalytic hydrogenation process under high-temperature and high-pressure conditions.Employing nano-iron as raw material,high-efficiency catalyst is prepared for the removal of highly toxic organic 4-NP in wastewater,aiming to reduce one waste pollution using other waste.The morphology and structure of the catalyst were characterized by XRD,TEM,XRF,SEM,EDS,XPS and BET,and the pollutant concentrations were measured by Uv-vis spectrophotometry.Taking p-nitrophenol（4-NP）as the target pollutant and NaBH₄ as the reducing agent,the catalytic performance of FeO_x and FeO_x@RGO materials was evaluated.Relevant work was carried out and the conclusions were summarized as follows:（1）Catalytic hydrogenation process was performed on rolling sludge,one of the hazardous wastes,under high-temperature and high-pressure conditions.The particle size was about 20nm,and its main phase Fe3O4 over the separated nano-iron.After activated by NaBH₄,the catalyst FeO_x consisted of both Fe3O4 and Fe⁰was prepared.The activity of results showed that 4-NP can be reduced to 4-AP only at the presence of both FeO_x and NaBH₄.The reduction kinetic of 4-NP by NaBH₄ catalyzed by FeO_x follows the quasi-first-order kinetic model,and the reaction activation energy Ea is33.71 k J/mol calculated by Arrhenius equation.The catalytic activity of FeO_x catalyst greatly decreased after circularly used trice.（2）To suppress the agglomeration and sinter of FeO_x particle accounting for the decreasing in catalytic activity,using FeO_x and graphene oxide（GO）as raw materials and NaBH₄ as reducing agent,FeO_x was loaded onto graphene leaves by a simple liquid phase reduction method to prepare magnetic nanocomposite catalyst FeO_x@RGO.FeO_x@RGO catalyst shows excellent characteristics for catalytic NaBH₄ reduction of4-NP,effects of different influence factors on the activity of the catalyst were investigated,using the control variable method,including the initial p H of the reaction system,the amount of catalyst,NaBH₄ concentrations,reaction temperatures.The reaction temperature was 25℃,with p H=8.7,FeO_x@RGO dosage was 0.6 g/L,NaBH₄concentration was 4 g/L,4-NP concentration was 200mg/L,the reduction rate was high at 99%in 70 s.The reduction of 4-NP by NaBH₄ over FeO_x@RGO catalyst foiiows the quasi-first-order kinetic model.The activation energy Ea of the reaction is calculated by Arrhenian equation to be 17.73 k J/mol,which is 15.98 k J/mol lower than that of the FeO_x catalytic reaction.The energy barrier of 4-NP reduction reaction can be greatly reduced compared with the same reaction over non-catalyst.The mechanism study shows that both 4-NP ions and BH4^-ions are negatively charged,and both reactants need to be adsorbed on the catalyst.BH4^-,on the other hand,produces active hydrogen atoms through the cleavage of boron-hydrogen bonds.The active hydrogen ion produced by BH4^-is considered to be the exact substance of the 4-NP hydrogenation reaction.In addition,the catalyst showed excellent catalytic performance in different water systems and good cycle stability in the cycle test.FeO_x@RGO showed its excellent performance in the catalytic 4-NP reduction by NaBH₄.It has various advantages in terms of simple preparation,friendly environment,wide application,convenient recycing,high efficiency and so on,thus,having wide application in wastewater treatment.