Study On The Remediation Of Heavy Metal Contaminated Agricultural Soil From West Of Yunnan Province By Chemical Washing And Phytoextraction

With the process of industrialization,the mining activities have become more and more frequent.For a long time,due to the influence of atmospheric deposition and surface runoff,the heavy metal pollution of farmland around the mining area has become increasingly severe.How to reduce remediation period and promote the removal efficiency are the main problems faced in the actual remediation process.In this study,an in-situ field experiment was conducted to investigate the feasibility of soil washing combined with repeated phytoextraction in remediating agricultural soil contaminated by multiple heavy metal.Secondly,to mitigate the negative impact of soil washing on the growth of Sedum plumbizincicola,sepiolite（S）,lime（L）,organic fertilizer（O）,maize straw（MS）and biochar（B）were applied to explore the effects of different amendment application on phytoextraction and the removal efficiency of the combined remediation technology.Finally,a pot experiment with the inoculation of exogenous functional bacterial（Rhodococcus sp.NSX₂）to search the micro mechanism of plant growth promoting rhizobacterial（PGPR）on phytoextraction after soil washing.The main conclusions are generalized as follows:（1）The removal efficiencies of Cd,Pb and Zn after soil washing and three successive crops of phytoextraction by S.plumbizincicola reached 71.0%,34.0%and47.8%,respectively,showed great potential for the remediation of heavy metals contaminated agricultural soil around mining area.In the soil washing process,the removal rates of Cd,Pb and Zn in F(40 mmol·L^-1 Fe Cl₃)treatment reached 35.2%,24.3%and 26.65%,respectively,were better than that of F+C(20 mmol·L^-1 Fe Cl₃+40 mmol·L^-1 citric acid).However,the shoot biomass of S.plumbizincicola in the F treatment showed significant 85.1%reduction indicted more negative impacts exerted on the growth of plant than F+C treatment.Thus,F+C were used as washing agent in the subsequent experiments.（2）It showed different effects on the growth of S.plumbizincicola and phytoextraction efficiencies after soil washing combined with phytoextraction,among which the lime and sepiolite played an important role in reducing soil acidity and heavy metal phytoavailable content after washing treatment while showed no effect on promoting the shoot biomass of S.plumbizincicola.Meanwhile,among the three organic material,the maize straw and organic fertilizer except the alkaline biochar could increase the biomass and heavy metal content in plant shoot to some extent,especially the maize straw not only improved the pore structure of the washed soil,but also increased the plant biomass by 24.2%significantly compared with the untreated group.After soil washing and the amendment enhanced phytoextraction,the removal efficiencies of Cd,Pb and Zn reached 58.6%,25.7%and 37.3%,respectively.（3）The 16s r RNA high-throughput sequencing result showed that the microbial community structure of rhizosphere soil of S.plumbizincicola had been changed significantly after washing treatment.Meanwhile,the amendment of maize straw and the inoculation of exogenous function bacterial reshaped the whole bacterial community structure in the rhizosphere and increased the OTU number.The results of carbon source utilization rate determined by Biolog-ECO showed the addition of maize straw and NSX₂ significantly increased the utilization rate which indicated the measures could improve the microbial community after washing treatment.Furthermore,the inoculation of NSX₂ have little effect on the increase of the shoot biomass while promoted the adsorption of heavy metals to increase the removal efficiencies.Thus,the removal rate of Cd,Pb and Zn reached 74.1%,34.7%and53.0%,respectively,after soil washing and the amendments.