Study On Remediation Of Heavy Metal Contaminated Soil By Modified Montmorillonite And Its Combination Biochar

Montmorillonite,which could achieve the retention of heavy metals through adsorption and cation exchange reactions,has been proven to be an effective material for immobilizing heavy metals.However,due to it hydrophilicity,the orginal montmorillonite was not widely used,and its modified forms were mostly concentrated in water treatment.Therefore,a magnesium modified montmorillonite was prepared in this study and used for the treatment of heavy metals contaminated soil.In addition,in order to better study the influence of magnesium modified montmorillonite on the microbial adversity of the whole soil system,biochar was added in the design process of the experiment,and modified montmorillonite and its combination with biochar were applied in different proportions(1:0,3:7;4:6;0:1)to remediate multi-heavy metal contaminated soil(Cu,Pb,Zn,Cd).The main contents of this study include: preparing magnesium modified montmorillonite,and characterizing and optimizing it;collecting soil from Yuelu Mountain in Changsha and adding different proportions of modified montmorillonite-biochar mixtures to soil.A soil experiment was conducted to analyze the effects of various proportions of remediation agents on physic-chemical properties,metal availability and toxicity,and microbial communities of contaminated soils.The results of this study are as follows:(1)Modified montmorillonite composite materials were prepared by calcining basic magnesium carbonate + glucose + montmorillonite,and the results of physicochemical characterization confirmed that the montmorillonite was successfully modified.It was found through adsorption experiments that Magnesium-montmorillonite(MgMt)has significantly increased adsorption of Cu and Pb,and has the potential to remediate heavy metal polluted soil.(2)Soil p H and water-soluble organic carbon(WSOC)increase as the ratio of Mg-Mt increases.Organic matter(OM)in soil increases as the ratio of biochar increases.(3)Due to the increase of p H value,soil remediation agents have significantly reduced the availability of heavy metals in compound contaminated soil.The minimum extractable concentration(TCLP)of Cu,Pb,Zn and Cd in the soil all appeared in group D,that is,only pure magnesium-montmorillonite was added.Among four heavy metals,the extractable concentration of Cu and Pb has the most significant decrease among the four heavy metals.(4)Different combinations of remediation agents all can reduce the weak acid extraction of the four heavy metals,promoting the conversion of the acid soluble state to the oxidation state and the residue state,which reduce the toxicity of heavy metals in soil.Among them,the acid soluble state concentration of Cu,Zn,and Cd increases with the increase of the ratio of Mg-Mt,and the lowest concentration appeared in group D.The concentration of acid soluble Pb did not has obvious proportional relationship with the addition of materials,because its lowest concentration appeared in group A.(5)The analysis results by high-energy sequencing technology showed that it can reduce the diversity of soil bacterial and have a greater impact om the stracture of bacterial communities when Mg-Mt alon existed.The addition of biochar can alleviate the material’s impact on the soil community,and weaken the negative correlation between the two factors(content clay and WSOC in soil)and soil bacterial.(6)In addition,magnesium-montmorillonite can promote the number of certain key bacteria and activate their activity,thereby reducing the bioavailability of heavy metals in the soil.