| E-waste dismantling plant is a typical compound contaminated site,where heavy metals including copper,lead and cadmium and organic pollutants such as polycyclic aromatic hydrocarbons,polychlorinated biphenyls,etc.coexist.Due to the illegal dismantling in the past,soil around the e-waste dismantling plant was also contaminated,which render the soil restoration difficult.Soil leaching,a fast and efficient remediation technology,has attracted more and more attention.Common eluents like ethylenediaminetetraacetic acid and diethyltriaminepentaacetic acid showed strong chelating ability to heavy metals,but their removal efficiency on organic pollutants was weak.Moreover,their non-biodegradability would affect the physicochemical properties of soil.Humic acid widely present in soil organic matter,which can complex with heavy metals and dissolve organic pollutants,and is considered friendly to soil.Natural organic acid possesses rich functional groups such as carboxyl and hydroxyl,which have strong heavy metal complexing ability to promote the dissolution of heavy metals in soil.Besides,because the surfactant could reduce the surface tension,it has a better solubilization capability on the insoluble organic pollutants.In this study,three eluents consisting of potassium fulvic acid,citric acid and sodium dodecyl sulfate were compounded.Their remediation effects and mechanisms of heavy metal contaminated soil and heavy metal/polychlorinated biphenyl compound contaminated soil around the e-waste dismantling plant were studied,and the changes of the physicochemical properties of the soil before and after leaching were explored.The main conclusions were as follows:(1)In the initial stage,the removal efficiencies of Cu and Pb increased with the increase of the eluent concentration.When the concentration of PFA was 3.2% and CIT was 0.16 mol/L,the removal efficiency did not change significantly with the increasing concentration of washing eluents.Therefore,the optimal compound concentration was3.2% PFA and 0.16 mol/L CIT solution.(2)By mixing 3.2% PFA with 0.16 mol/L CIT at a volume ratio of 4:1,the best removal efficiencies of Cu and Pb were 42.92 and 50.46%,respectively,after reacting for 6 hours at a water-soil ratio of 20:1 under the original p H condition.(3)Compared with single leaching agent,the compound eluent not only increased the total removal efficiency of heavy metals,but also enhanced the stability of residual heavy metals in soil.More importantly,it had less impact on the physicochemical properties of soil such as p H,organic matter,cation exchange capacity,ammonium nitrogen,available phosphorus,rapidly-available potassium and soil enzyme activity.(4)When the compound concentration of PFA-CIT was unchanged,the removal efficiency of the compound eluent for PCB28 and PCB153 could be promoted by adding SDS.The removal efficiency increased with the concentration increasing,until the concentration was higher than 1.5%,at which the removal efficiency was not improved significantly.While the addition of SDS had little effect on the removal efficiency of heavy metals.(5)1.5% of SDS was added to the PFA-CIT system,the best removal efficiencies of Cu,Pb,PCB28 and PCB153 in soil were 46.12,49.73,61.48 and 68.67%,respectively,after reacting for 12 hours at a water-soil ratio of 20:1 under the original p H condition.(6)Under the same conditions,the overall removal efficiencies of Cu,Pb,PCB28 and PCB153 by adding the eluent in two equal amounts was better than by adding the eluent in one or three times.(7)X-ray diffraction,X-ray photoelectron spectroscopy,scanning electron microscopy and energy spectrum analysis,fourier transform infrared spectrometer and other characterization analysis showed that the leaching agent would not undergo oxidation-reduction reactions with the pollutants.The leaching agent was firstly adsorbed on soil surface,and the pollutants were desorbed and eluted from a mineral component of the soil through acid dissolution,solubilization and complexation. |
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