Chemical Speciation Distribution Of Heavy Metal In The Soil Of Typical Lead-zinc Smelter And Speciation Mechanism Of Cadmium Passivation By MICP

The history of heavy metal pollution in smelting site soil is se-rious.Microbial induced carbonate precipitation（MICP）can passivate heavy metals and reduce their migration performance,but the related pas-sivation mechanism is not clear.Therefore,this study focused on a typical lead-zinc smelter in the hilly region of south China,and studied the total amount and chemical speciation of typical heavy metals Cd,Pb and As in the soil by sequential extraction method.The distribution of microbial community structure was studied by high-throughput sequencing technol-ogy.The interactions between microbial communities and the chemical speciation of Cd,Pb and As were studied using random forest model.MICP functional bacteria were selected to passivate Cd in contaminated soil around the site,and the mechanism of Cd passivation in soil was analyzed through MICP functional bacteria mediating soil coexisting ion reaction.The main conclusions are as follows:1)The total concentration of heavy metals in the site was Pb>As>Cd,and the main speciation of Cd,Pb and As are exchangeable fraction、Fe-Mn oxides bound fraction and Fe-Al oxides bound fraction,The order of migration coefficient is Cd>As>Pb.Proteobacteria and Stenotropho-monas are the dominant microorganisms at phylum and genus levels re-spectively.The effect of microorganism on Cd morphology was greater than that of Pb and As.2)Bacillus cereus with MICP function can reduce the content of ex-changeable fraction of Cd in contaminated soil,and increase the content of carbonate bound、Fe-Mn oxides bound and residual fraction.Thus,the bi-oavailability of Cd is reduced and Cd in soil was passivated.3)The mechanism of MICP functional bacteria passivation of Cd in soil can be attributed to:MICP functional bacteria mediated soil coexisting ion reaction directly generated Cd CO₃;coprecipitation with Ca CO₃;Al₂Fe O₄、Fe OOH、Al（OH）₃ were formed to adsorb Cd.