Study On Remediation Of Polychlorinated Biphenyls Contaminated Soil By Oyster Shell Modified Materials

Polychlorinated biphenyls(PCBs)are typical persistent organic pollutants.It has the characteristics of difficult degradation,high enrichment and long-distance migration.Soil is the ultimate destination of the PCBs which have entered the environment.Therefore this will eventually cause the soil pollution of PCBs.At present,the situation of PCBs contaminated soil is serious in China.However,there is still lack of cost-effective remediation methods for the PCBs polluted soil,and this make it as a potential hazards for the environmental safety and human health.Oyster shell is not only a natural soil conditioner,but also anexcellent carrier of composite materials.When the oyster shell is used alone,its ability to repair the contaminated soil is limited.In this paper,the materials of nanometer iron modified oyster shell were prepared by loading nanometer iron to oyster shell.The superior chemical dechlorination performance of nanometer iron makes the modified materials possess the abilities of soil improvement,pollutants adsorption fixation and chemical degradation.Firstly,the removals of PCBs in the solution by the modified material were investigated;Base on this,the effects of the modified materials on the remediation of PCBs contaminated soil were studied;finally,to explore the immobilized and degradation mechanism of PCBs in the soil by the modified materials,the kinetics and adsorption isotherm model were studied by fitting the experimental data.The main results are as follows:(1)The microstructure characterization of the modified oyster shell materials by the in situ-reduction load method showed that the nano iron was uniform in size,and highly dispersed,and tight coupled with the oyster shell.The dispersion and oxidation resistance of the nano iron have been improved obviously,and the morphology and structure of the modified oyster shell materials are not affected.(2)The experimental results of PCBs removal from solution by the modified oyster shell materials showed that the effect of initial concentration and solution temperature on the removal efficiency was greater than that of solution pH.When the dosage of the materil is 0.03g,the initial concentration of PCBs is 5mg/L,and the solutin temperature and pH are 25 ? and 7 respectively,the removal rate of modified materials can reach 96%.Compare to the nano iron individual,the modified materials has longer service life.(3)The experimental study on the remediation of PCBs contaminated soil by the modified oyster shell materials showed that the effects of soil temperature and moisture content on the remediation of PCBs in the soil were similar,showing a increase in the first and then remaining stable;The adsorption rate decreased with the increase of the organic matter in the soil.The adsorption process was matched with the pseudo two order kinetic model.The initial stage of adsorption is controlled by the internal diffusion,and then the film diffusion has great influence on the adsorption.In the isothermal adsorption models,the Langmuir equation can well describe the isothermal adsorption behavior of the modified materil on PCBs.The remediation of PCBs contaminated soil by the modified material is the combined effect of physical adsorption and chemical dechlorination.