Remediation Technology Research For Heavy Metal Contaminated Soil In Road Traffic

With the rapid development of road traffic in China,heavy metal contamination in soils,especially along the roadside,has seriously affected the surrounding environment and human health.In order to solve the heavy mental contamination problem,it is necessary to use effective geological environment technology to remediate the traffic heavy metal contaminated farmland,which is of great significance to ensure the quality of agricultural products and human health.At present,solidification/stabilization remediation technology has become the research hotspot of soil heavy metal remediation due to its advantages of harmless,cheap and efficient.In this paper,inorganic adsorbent zero-valent iron(ZVI)was used as the research material.Through adsorption experiments and adsorption model fitting,the ZVI effect on adsorption characteristics of Pb(?)and Cd(?)under different influence factors was explored.The ZVI effect on speciation changes of Pb(?)and Cd(?)in soils was tested by incubation experiments combined with Tessier sequential extraction procedure(SEP).Based on unconfined compressive strength test and polynomial equation fitting,the ZVI effect on mechanical properties of Pb(?)and Cd(?)heavy metal contaminated soil was studied.Through various detection methods(SEM,XRD and BET-N2),micro characterizations of ZVI before and after remediation were carried out to explore the remediation mechanism of ZVI.The effects of ZVI on soil pH value,heavy metals accumulation in rice and soil,and rice yield were studied through field experiments to verify the long-term effectiveness of ZVI.Finally,COMSOL software was used to simulate the diffusion and migration of pollutants in polluted soil,and to explore the different influence factors effect on the time of pollutants breaking through the plough layer.The results are summarized as follows:(1)The final removal rate of lead by ZVI was 98%,and the highest removal rate of cadmium was 88%.Freundlich isotherm and Pseudo-first order kinetic model matched the Pb(?)adsorption process,while Langmuir isotherm and Pseudo-second order kinetic model fitted the Cd(?)adsorption process well.The maximum adsorption capacity predicted by Pb(?)and Cd(?)adsorption reached 88.3 and 34.7 mg/g,respectively,and the adsorption equilibrium time of Pb(?)was much shorter than Cd(?)adsorption.(2)In heavy mental contaminated soil,with the increase of ZVI dosage,the Fe/Mn oxide bound fraction and carbonate bound fraction were effectively converted into residual fraction,and the leaching concentration of pollutants gradually decreased.0.4%ZVI was conducive to Pb(?)contaminated soil treatment,while 0.1%?0.2%ZVI had the best fixation effect on Cd(?)contaminated soil.(3)The strength and deformation effect of ZVI on heavy metal contaminated soil was positively correlated with the ZVI dosage,but negatively correlated with the initial heavy metal concentration.Different heavy metal had different effects on the mechanical properties of soils.In terms of compressive strength and deformation modulus,non-polluted soil>Pb(?)polluted soil>Cd(?)polluted soil;in terms of failure strain,Cd(?)polluted soil>Pb(?)polluted soil>non-polluted soil.The increase of ZVI dosage led to the strengthening of soil brittleness,while the increase of heavy metal concentration led to the strengthening of soil plasticity.The stress-strain curve of Pb(?)and Cd(?)contaminated soil solidified with ZVI could be effectively estimated by the one-element six-order empirical equation.(4)Mesoporous ZVI was used to remediate Pb(?)and Cd(?)polluted soil,and the mechanism of action was basically similar.The chemical adsorption including redox and surface complexation is the main reaction process,which can effectively reduce the bioavailability of Pb(?)and Cd(?).(5)The field experiments showed that ZVI had a good long-term performance.The reasonable application of ZVI could effectively reduce the available Cd accumulation in soil and rice.Besides,it could improve rice yield and reduce soil acidification,which provided the practical basis for the effective remediation of heavy metal contaminated soil by ZVI.(6)Through the numerical simulation of finite element software,the time for pollutant to break through the topsoil was positively correlated with the ZVI dosage,and negatively correlated with the rainfall and initial pollutant concentration.The time to penetrate the topsoil was the most sensitive to changes of ZVI dosage,followed by rainfall,and the initial pollutant concentration was the smallest.