Preparation Of Schwertmannite Composite And Its Adsorption Effect And Mechanism For Arsenic

With industry developing,more and more arsenic enters into the land and water,causing great harm to human and ecological environment.Arsenic pollution has become a worldwide problem.In the face of such a serious and challenging arsenic pollution situation,people have a stronger demand for arsenic pollution remediation.The remediation technology of arsenic pollution is becoming more and more diversified.Chemical passivation technology has been widely concerned because of its advantages of quick effect and simple operation.In recent years,composite materials prepared on the basis of ironbased minerals have achieved good results in the treatment of soil arsenic pollution,so they have received widespread attention.This topic uses waste wheat straw biochar as a carrier to prepare a composite material of schwertmannite through a liquid phase reaction method.The adsorption effect and adsorption mechanism of arsenic were studied through aqueous solution experiments and a series of characterization methods.The arsenic in the soil samples treated by the soil stabilization experiment was extracted by grades to study its passivation characteristics of the soil heavy metal As form,and Then through the analysis of the microbial community,study its impact on the soil microbial community.The main research results obtained are as follows:(1)The characterization results of BET,SEM,XRD,FTIR showed that schwertmannite particles were uniformly loaded on the biochar,and schwertmannite composites were successfully prepared.The Sch-BC material contains abundant oxygen-containing functional groups such as-OH,C-O,and C=O.In addition,the schwertmannite particles in Sch-BC are adequate distribution on the surface of the biochar,which obviously reduces the aggregation of schwertmannite particles,and obviously improve the stabilization and specific surface area of schwertmannite,which provides more active sites for the adsorption of As(?).(2)The optimal ratio of Sch-BC is Fe:BC(mass ratio)=1:1.Compared with the original biochar,the adsorption capacity of As(?)by Sch-BC is significantly increased.The adsorption effect is significantly improved.Sch-BC has almost no effect on As(?)in the range of pH=2-8,and has a high removal rate and adsorption capacity.Temperature has little effect on the removal of As(?)by Sch-BC.It is the best choice to remove As(?)in aqueous solution at room temperature of about 25?.Sch-BC is not affected by the coexisting ion SO42-in the process of removing As(?).When the molar ratio of PO43-and SiO32-to As(?)rises to 375:1,there will be a greater impact,but the water body or actual PO43-and SiO32-in groundwater are low,so it will not affect Sch-BC's removal of arsenic pollution from natural water bodies.The process of As(?)removal by Sch-BC is in accordance with pseudo second order adsorption kinetic and Langmuir isothermal absorption models,and the adsorption may be mainly chemisorption.The adsorption rate of As(?)by Sch BC is controlled by surface adsorption and intra particle diffusion.(3)The surface of Sch-BC biochar is rich in many effective functional groups,such as-OH,C=O and C-O,which can react with arsenate ion to form complex and adsorb on the surface of biochar.Fe(?)in schwertmannite particles combines with As(?)through chemical bonds to form As(?)-Fe(?)SO42-complexes,which are adsorbed to the surface.At the same time,the internal sulfate of schwertmannite can be ion exchanged with arsenate ions,so as to achieve the purpose of removing As(?).(4)Soil experiments show that different treatments such as BC(1%,3%,5%),Sch(1%,3%,5%),Sch-BC(1%,3%,5%),etc.In the soil,the proportion of occurrence forms that are easily absorbed and utilized by organisms has decreased,while the proportion of the more stable crystalline hydrous oxide combined state has increased.The proportion of residual fraction did not increase significantly.The main reason is that the period of stabilization experiment is short and the form of arsenic is not stable.The results showed that among the three materials,Sch-BC had the best stabilization effect on arsenic in soil.After five weeks of treatment,the proportion of the relatively stable Crystal-line hydrous oxide increased by 28%,and it has been determined that 3%Sch-BC is the best addition ratio.The analysis of the microbial community in the soil under different treatment conditions showed that soil arsenic pollution will affect the diversity and structure of soil microbial communities.Arsenic-tolerant bacteria are more likely to survive and multiply in arsenic-contaminated soil,and their relative abundance is the highest.At the same level of addition,compared with the original soil,the OTU number of CK group without chemical addition increased by 166.The OTU numbers of BC,sch and Sch-BC were 139,61 and 107,respectively.Among them,schwertmannite have a greater inhibitory effect on the reproduction of microorganisms.The cause may be that the iron in the minerals will be combined with organic matter,which in turn affects the decomposition of organic matter by microorganisms.Comprehensive stabilization effect and microbial community analysis results,schwertmannite composite material not only has a good repair effect on arsenic in the soil,but also greatly reduces the inhibition of the growth and reproduction of the microbial community,and reduces the risk of soil toxicity to organisms.