Effect Of Modified Silkworm Sand Passivating Materials On Remediation Of Antimony Contaminated Soil And Its Mechanism

At present,the farmland soil in some areas of Guangxi Autonomous Region of my country has been contaminated by antimony（Sb）.Excessive Sb can significantly inhibit the growth and yield of crops and seriously threaten the health of local residents in the contaminated area.Our previous research shows that silkworm excrement can passivate and repair soil contaminated by arsenic（As）,cadmium（Cd）,and lead（Pb）,and significantly reduce the absorption of these elements by rice,but the mechanism is still unclear.As and Sb have similar chemical properties,it is unknown whether silkworm excrement can be used to passivate and repair Sb contaminated soil.Based on this,this study uses silkworm excrement as the research object,through physical（made of biochar）and chemical（Fe modification and sulfhydryl modification）modification methods to prepare different passivation materials,using a series of analysis and detection methods to compared and studied the physical and chemical properties of these materials; combined with adsorption experiments,the adsorption performance and mechanism of different passivation materials for different forms of Sb were explored;at the same time,pot experiments verified that the above-mentioned materials can be used for passivation and repair of heavy（type）metals（including As,Sb,Cd,Pb,etc.）.The main results obtained are as follows:（1）The sulfhydryl modified silkworm excrement biochar material（MPBC）was successfully prepared by the MPTMS ethanol phase acid catalyzed soaking method.The sulfur（S）element content of the material increased significantly from 0.063%before modification to 1.762%.It is 28 times the S content before modification.Iron modification successfully loaded Fe element on biochar（MBC）,and the Fe content of MBC was as high as 70228 mg kg^-1.Compared with the original silkworm excrement（Cs）,the specific surface area and internal pore volume of the modified biochar material are significantly reduced,and the four materials have good thermal stability.The changes of functional groups of silkworm excrement and its modified materials were analyzed by Fourier Transform Infrared Spectroscopy（FTIR）,and it was found that compared with CS,MPBC has higher sulfhydryl and carboxyl groups,but reduced hydroxyl and amino groups.The content of S on the surface of MPBC can reach 2-3 times that of CS.CS and biochar modified silkworm excrement（BC700）have higher pH.After sulfhydryl modification,the pH of MPBC is close to neutral,while the pH of MBC is acidic.（2）The adsorption process of Sb by the four materials conforms to the Langmuir isotherm adsorption equation,which is a single-layer adsorption.The adsorption process of Sb by MPBC conforms to the second-order kinetic equation,and the adsorption behavior is chemical adsorption.Under acidic conditions,CS,BC700 and MPBC have better adsorption effects on different forms of Sb;while under alkaline conditions,it is not conducive to the adsorption of Sb by the above-mentioned materials.But for MBC,its adsorption capacity for Sb under alkaline conditions tends to increase,especially for trivalent antimony.（3）The test soil is severely polluted by Sb,As,Cd,Pb,and Cu,and its comprehensive potential ecological hazard index（RI）is as high as 1614.7,which is a very high risk.Compared with the control,after adding CS,BC700,and MPBC to the soil,the biomass of pakchoi increased significantly;but MBC treatment caused the death of pakchoi,which may be related to the higher Fe content in the soil and the higher Fe content or activity in MBC.After adding CS,BC700,and MPBC,the biomass of pakchoi increased significantly,and the growth-promoting effect was:CS>BC700>MPBC.The above-mentioned growth-promoting effects may be related to:1.Silkworm excrement and its modified materials contain a large number of essential nutrients for plants;2.Inhibition of the absorption of heavy metals.Although MPBC inhibits pakchoi with the strongest ability to absorb heavy metals,it contains less nutrient elements,which makes its growth-promoting effect worse than the other two materials.