Study On The Solidification And Stabilization Of Heavy Metal Lead In Soil By Apatite-sesame Straw Composite

In recent years,the soil heavy metal pollution in farmland and mining areas has become increasingly serious,so finding cheap and environmentally friendly heavy metal remediation materials to solidify and stabilize soil heavy metals is a research hotspot and urgent need.Some scholars have found that biochar,as a new passivator,shows great potential in improving soil physical and chemical properties and reducing heavy metal pollution,and its addition to heavy metal contaminated soil can effectively achieve soil remediation.Henan Province is a major sesame growing province in China,but about half of the sesame straw is not effectively used every year,which causes a great waste of resources.In addition,studies have shown that phosphorus has a strong affinity for metal cations and can effectively fix heavy metals in soil.In this paper,the removal effect,adsorption mechanism and influencing factors of biochar on Pb²⁺in water were discussed through batch adsorption experiments,and the effects of biochar on soil physical and chemical properties,the morphological distribution of soil heavy metal Pb and the growth and development of rapid cabbage in four seasons were studied by batch adsorption experiments.The main conclusions are as followed:（1）The original biochar（BC）was prepared by pyrolysis of sesame straw biomass as raw material at a high temperature of 550°C,and chloroapatite and hydroxyapatite were co-impregnated with the original sesame straw biochar（BC）to obtain chloroapatite-modified biochar（BC-Cl）and hydroxyapatite-modified biochar（HBC）.Through the analysis of SEM,XPS,FTIR and XRD,it can be seen that chloroapatite and hydroxyapatite are successfully loaded on the surface of biochar,but the skeleton structure of biochar itself is not damaged,and the modification method also increases the type,number and number of functional groups on the surface of biochar and the number of adsorption points.（2）The adsorption test of Pb²⁺in water by modified biochar shows that biochar prepared by co-impregnation of chloroapatite and biochar has a better adsorption effect on heavy metal Pb²⁺.The overall adsorption test showed that when the solution p H=5,the addition amount of BC-Cl was 600 mg·L-1,biochar has the best removal effect on Pb²⁺.The adsorption of Pb²⁺by BC-Cl is more in line with the quasi-secondary kinetic equation,indicating that the adsorption process is mainly chemical adsorption.The adsorption process of BC-Cl to Pb²⁺was more in line with the Langmuir isothermal adsorption model,indicating that the adsorption process was mainly monolayer adsorption.In addition,phosphorus plays an important role in the adsorption of Pb²⁺by modified biochar,and the main reason for the high removal rate of Pb²⁺by BC-Cl is that PO₄^3-produced by the dissolution of chloroapatite can precipitate with Pb²⁺,and then generate phosphate precipitation that is difficult to dissolve in water.（3）The results of 90 days soil culture remediation test showed that compared with the control group CK（no added biochar）,the effective phosphorus content and cation exchange in the BC,BC-Cl and HBC treatment groups could significantly increase the effective phosphorus content and cation exchange amount of soil.The addition of biochar not only significantly reduced the TCLP extraction content of Pb in soil,but also promoted the transformation of heavy metals from unstable forms such as weak acid extraction to more stable residue states.The experiments showed that the remediation effect of 5%BC-Cl was the best,which reduced the reducible Pb content in soil by 26.36%compared with the control group,and increased the residual Pb content by 103.53%.（4）The results of the four-season rapid cabbage cultivation test showed that BC,BC-Cl and HBC could effectively increase the chlorophyll content of plant leaves,significantly reduce the heavy metal content of some leaves,improve the growth quality of plants to a certain extent,and promote the growth and development of plants.In summary,the inorganic material apatite modified sesame straw biochar has high removal rate and excellent adsorption performance for Pb²⁺in water,which can passivate and remediate heavy metal contaminated soil,and is a promising environmental Pb remediation material.It can be seen that apatite-modified biochar has played a positive role in improving soil physical and chemical properties,promoting the transformation of heavy metal Pb to a more stable residual state,promoting the growth and development of plants and reducing the heavy metal content in their bodies.