Leaching Heavy Metals Contaminated Soils From An Electronic Waste Recycling Site

Nowadays, electronic waste has become the fastest growing municipal solid waste.China is the hardest-hit areas dismantling of electronic waste in the world, as there’renumerous harmful substances in electronic waste. Because it was dismantled with originalmethod，it bring about serious pollution problems from heavy metal and persistent organicin the local environment (soil, water, air). Chemical leaching remediation technique is asimple, efficient and promising Heavy metal in soil remediation technology. This studyinvestigates the leaching of a soil contaminated mainly with Cu and Pb by dismantling ofelectronic waste in the Longtang Town of Guangdong provinceIn this study, six common agents were selected as the eluent, including HCl,sodium thiosulfate, citric acid, tartaric acid, oxalic acid, EDTA and different combinationsof eluent. Studied the repair efficiency of the contaminated soil in electronic wastedismantling space,and before and after restoration the variation characteristics of heavymetals formation in soil. The results show:（1）HCl, sodium thiosulfate, citric acid and EDTA can effectively remove Cu in thesoil, HCl and citric acid removal rate can reach more than70%, sodium thiosulfate andEDTA reached50%. The removal rate of Cu and the concentration of eluent were positivelycorrelated. With the increase of the eluent concentration increases, tartaric acid removal ofthe cu with increasing concentration first and then decreased, oxalic acid almost cannotremove Cu and with the increase of the concentration decreases. The removal rate of Pb fordifferent eluent is small, removal rates between1.15%～18.40%. The eluent concentrationwas significant positive correlated with the removal rate of Pb (P<0.01),HCl and oxalicacid removal rate is highest,17.29%and18.40%respectively, EDTA removal rate reached10.36%, citric acid and tartaric acid removal rate was2.45%and4.50%, sodium thiosulfateremoval rate of Pb is Worst,just1.15%.（2）With the increase of reaction time the removal rate of Cu and Pb is increased,wassignificant positive correlation(P<0.01).The main reason is that as the extension of elutiontime between soil particles and eluent completely reaction,the more heavy metals wereremoved.With the decrease of the ratio of soil to water, unit of the amount of soil eluentcontent increases,the removal rate Cu, Pb is increased.（3）Mixed eluent of EDTA and sodium thiosulfate can removal more heavy metalsthan single eluent, especially Pb.（4）Analyzing before and after leaching the different forms content of Cu and Pb inthe soil, the main removal Cu is carbonate bounded form, Fe-Mn oxidation form, andresidual form, except oxalic acid. Both leaching before and after the Pb mainly exists formsis residual fraction, except that oxalic acid little change the content of each forms. （5）The desorption process of Cu and Pb from soils with different eluent applicablekinetics equation is different, the process of Cu than Pb is more suitable for simulation ofdynamics equations.HCl, citric acid, tartaric acid, and mixed eluent of EDTA and sodium thiosulfate wasused in column leaching test. Through the column leaching test, we can investigate theremoval rate of Cu and Pb and analyze leaching before and after the content and differentforms at different depths. The results show:（1）The removal rate of Cu by HCl and citric acid is more than67%, EDTA andsodium thiosulfate mixed eluent and tartaric acid is57.70%,46.75%, respectively. EDTAand sodium thiosulfate mixed eluent is best removal efficiency of Pb that the removal rateis16.23%, followed by HCl is12.65%, Citric acid and Tartaric acid is about8%.（2）Two heavy metals content of the eluent breakthrough curve showed firs increasesand then decreases, the content of Cu is much higher than Pb, and the penetration point ofPb lagged behind Cu.（3）After leaching for HCl and citric acid the Cu and Pb each forms were reduced, fortartaric acid the Cu exchangeable forms were increased and Pb each forms were reduced,for EDTA and sodium thiosulfate mixed eluent the Cu organic forms were increased a lot.Two kinds of heavy metals for different eluent remove regularity is not obvious in depth.