Research On Co-remediation Of Heavy Metal Contaminated Soil In Mining Area By Heat-transformed Sawdust And Herbaceous Plant

Due to the low remediation efficiency of heavy metal pollution in the mining area,it has become a hot research topic to explore efficient remediation technologies to restore the normal function of the soil.According to the characteristics of soil pollution in Hezhang,Guizhou,this study used sawdust ash(SA)and sawdust biochar(SB)in combination with Medicago sativa L.,Festuca arundinacea,and Orychophragmus violaceus to remediate soil that contaminated by Pb,Zn,Cd and As in mining area,and analyzed the co-remediation process and mechanism.According to the analysis of heavy metal pollution in the soil from mining area in Hezhang County,it was found that the content of heavy metal in the study area was greatly exceeded the background value,and As,Cd,Cu,Pb and Zn were mainly from mining and smelting activities.The assessment of heavy metal pollution showed that the concentration of heavy metals in Magu soil was high,and the potential risk reached the level of serious pollution,among which Pb,Zn,As and Cd were the main elements that cause soil pollution in Magu mining area.The heavy metal adsorption characteristics of heat-transformed sawdust showed that SA had a strong adsorption capacity for Zn,with a maximum adsorption capacity of 17.91 mg/g;the maximum adsorption capacities of SB for Pb,As and Cd were 72.10,1.53,and 19.76 mg/g,respectively.The remediation mechanism of heavy metal pollution confirmed that the passivation of Pb by adding materials was achieved by promoting the transformation of PbO into(CH3COO)2Pb and PbSO4 in the soil.The remediation potential of materials showed that adding SA and SB at a ratio of 1:1 and 1:2 significantly reduced the bioavailability of heavy metals and the potential ecological risk of soil pollution.Herbaceous plant remediation had shown that Medicago sativa L.had a strong bioaccumulation and transport capacity for Cd,which concentration in shoot was 117.18 mg/kg.Festuca arundinacea had the strongest ability to absorb and tolerate composite heavy metals,and the remediation process could significantly improve soil enzyme environment and microbial community diversity.The combination of Pb and organic acids was an important mechanism to reduce the toxicity of heavy metals to plant,and the proportion of lead malate in Festuca arundinacea was 58.0%.According to the analysis of the remediation potential of soil pollution,Festuca arundinacea was a better heavy metal remediation plant.The experimental result of the co-remediation of heat-transformed sawdust(The mass ratio of SA to SB is 1:2)and plant showed that the removal rates of Pb,Zn,Cd and As were the highest under the treatment of Festuca arundinacea combined with 5%material,which were 18.02%,22.15%,22.05%and 12.47%,respectively.The distribution of heavy metals in plant subcellular showed that the accumulation of Pb,Zn,Cd and As in the cell wall of Festuca arundinacea root was significantly increased by adding 2%materials,and the concentrations in the cell wall were 218.21,4486.25,33.59,and 124.15 mg/kg,respectively.Co-remediation can promote the formation of organic acids-Pb-cell wall structure,which was an important way to improve the resistance of plants to heavy metal damage.The combination of 2%material and Festuca arundinacea could effectively remove heavy metals in the soil,and enhanced the detoxification ability of the plant,which was a better way to improve the soil environment and remediate the compound heavy metal pollution.This study provided a new idea and theoretical reference for the research and application on remediation of heavy metal contaminated soil in mining area by existing components and distribution characteristics of heavy metals during the remediation process.