Removal Of Heavy Metals In Landfill Leachate Using Nano-iron/oyster Shell Composites

In recent years,heavy metal pollution in landfill leachate has been increasingly serious in China and caused severe damages to the ecological environment and human health of some areas.On one hand,heavy metal in landfill leachate not only causes environmental pollution but also influences the biochemical treatment effects of leachate.On the other hand,as a kind of natural water quality ameliorant and a good carrier of composite materials,oyster shell has not been sufficiently and efficiently utilized.In the research,nano iron was introduced to oyster shell to prepare composite materials,and the resource utilization of such materials in processing heavy metal in landfill leachate was discussed as well.The research has certain theoretical and practical significance in terms of material preparation,resource utilization of oyster shell and environmental pollution control.First of all,the in situ liquid phase reduction method was used for the research to prepare nano iron/oyster shell(NI/OS)composite materials;in addition,the efficiency of such composite materials for processing four typical heavy metals,Cr(?),Cd(?),Zn(?)and Pb(?),in simulated landfill leachate was examined as well.The impacts of landfill leachate ingredients such as organic matters and ammonia nitrogen on the removal efficiency were discussed;based on the representation results of such composite materials before and after the reaction,the mechanism of such composite materials for removing heavy metal in landfill leachate was analyzed.Finally a preliminary study on the actual removal efficiency of such composite materials for removing heavy metal in landfill leachate was conducted.The major research results are as follows:(1)In the experiment of using composite materials to remove the heavy metal in simulated landfill leachate,the single factor and orthogonal experimental results showed that:The initial pH of the solution and the initial concentration of heavy metal ions had large impacts on the treatment efficiency of such composite materials;while the response surface optimization experimental results showed that:the fitting experimental data of the quadratic function model were relatively remarkable;in the BBD model design experiment,the effects were favorable by performing the experiment as per the optimization conditions.(2)According to the research of the impacts of landfill leachate ingredients on composite materials for removing heavy metal:under different concentration ratios,the removal rates of metal ions were Pb(?)>Cd(?)>Zn(?)>Cr(?);the addition of organic matters and ammonia nitrogen had the largest impacts on Pb(?)among the four typical heavy metals.(3)According to the mechanism research on composite materials for removing heavy metal in landfill leachate:The impacts of composite materials on heavy metal included physical and chemical processes;Langmuir isotherm model was suitable for describing the adsorption process of the three heavy metals,namely Cr(?),Zn(?)and Pb(?),Freundlich isotherm model was suitable for Cd(II);the removal processes of Cr(?),Cd(?),Zn(?)and Pb(?)accord with the pseudo-second order kinetics.(4)Study on the removal of heavy metals from actual landfill leachate by composite materials:similar to the simulation results,pH is a key factor affecting the experiment;Cr(?)and Cd(?)in the heavy metals of com-posite landfill leachate both Zn(?)and Pb(?)have good removal effects.The composite material has certain practical value in the treatment of heavy metals in landfill leachate.