Study On Synthesis Of Activated Carbon Supported Nano Zero-valent Iron And Application In Hexachlorbenzene Adsorption

Hexachlorbenzene?HCB?,one of the 12 persistent organic pollutions,has carcinogenic,teratogenic and mutagenic effects.It could lead to kidney and liver damage,stagnant growth,and even be genetic.It is important to environmental protection and human safety maintenance for the HCB reduction in wastewater.Activated carbon and nano zero-valent iron?nZVI?are widely used as the effective dehalogenation ability to lower or eliminate the organic matters' toxity.In this research,impregnation method and adsorption method were adopted to synthesis activated carbon supported nZVI?nZVI/AC?,determining the optimal synthesis condition.And the HCB removal efficiency,representing organic matters,and mechanism by composite materials were investigated.Characterization and adsorption equilibrium experiment results showed Fe:C mass ratio,heat time and ethanol additive amount had significant effect on the iron loading.That specific surface area and pore volume of activated carbon have decreased after nZVI loading,and the reduction range is related to iron content.But high iron contend does not necessarily contribute to HCB degradation.For nZVI/AC-I prepared by impregnation method,when Fe:C ratio at 0.84:1 and heat time at 5 h was selected,the HCB removal efficiency was highest and maximum adsorption capacity reached 4.87 mg/g.But to adsorption method,nZVI/AC-A particle with Fe:C ratio at 0.42:1 and ethanol dosage at 26.78% had the optimal HCB removal efficiency and maximum HCB adsorption capacity 10.22 mg/g.Comparing with virgin activated carbon,the HCB removal efficiency by nZVI/AC was greatly improved.By optimizing the synthesis conditions of two methods,batch experiments were conducted to discuss the effects of different environmental conditions on HCB removal,such as reaction time,solution pH and the presence of cation and anion in water.The results illustrated nZVI/AC particles were capable of reducing the HCB concentration quickly and effectively,and that adsorption kinetics was consistent with pseudo second reaction model.The pH experiment showed as the different iron content,nZVI/AC-I had the best efficiency at pH 5⁷,but it was best at acidic condition for nZVI/AC-A.The HCO₃^-,Cl^-,SO₄^2-and Mg²⁺ in water enhanced the HCB removal by nZVI/AC to a variable extent;but NO₃^-inhibited the HCB adsorption reaction of nZVI/AC-A,and improved that of nZVI/AC-I;And Fe²⁺ and Cu²⁺ improve the removal efficiency of nZVI/AC-A,but decreased that of nZVI/AC-I.In addition,this study also investigated the HCB degradation products and pathway.It was a clear stepwise dechlorination pattern.Due to the high efficiency of nZVI/AC,HCB could be degraded to monochlorobenzene?MCB?.But as the symmetric structure of tetrachlorobenzene?TeCB?and dichlorobenzene?DCB?,stable nature,they were main products.The two reaction pathways were similar,but the activity of nZVI/AC-A was stronger,so the HCB reaction was more thoroughly and removal efficiency was higher.