Effect Of Biochar-Metal Oxides Composite Material On Bio-Availability Of Arsenic

In the south of China,especially in the Xiangjiang River basin,arsenic（As）pollution in soils has become more and more serious.Controlling farmland As pollution and ensuring rice quality and safety has become a research hotspot in recent years.In this study,biochar（BC）was used as a raw material,and biochar-metal oxide composite materials（FMBCs and FMLBCs）were prepared by impregnation method.The composite materials with good adsorption effect were screened out.Based on this,the effects of biochar-metal oxide composites on the effectiveness of As were studied through batch adsorption experiments,As volatilization experiments,and pot experiments,and clarified the biochar-metal oxide composites on As-contaminated rice fields Soil regulatory mechanisms.The following results have been achieved:（1）Screen Biocar-metal oxide composites with better adsorption effect through adsorption experiments.Biochar-Fe-Mn-La oxide composites（FMLBCs）have a better adsorption effect on arsenic than Biochar-Fe-Mn oxide composites（FMBCs）,and as the amount of La added increases,FMLBC has a better adsorption effect on arsenic.With the increase of FMLBC₁ dose from 2 g/L to 16 g/L,the As removal rate increased from 38.3%to 84.0%.For FMLBC₂ and FMLBC₃,the As removal efficiency increased from 51.4%to 96.8%and from 53.3%to 99.7%,respectively.（2）The mechanism of adsorption of arsenic by FMLBC was studied by adsorption experiments and analytical methods such as XPS and FTIR.The maximum As（III）adsorption capacity of FMLBC is 1.57 and 3.99 times higher than that of FMBC and BC,respectively.The mechanism of As adsorption on FMLBC involves oxidation,electrostatic attraction,ligand exchange,and formation of inner R-O-As complexes.Among them,electrostatic attraction and inner layer complexation are relatively large.（3）The effect of the addition of FMLBCs on arsenic volatilization in paddy soil was studied by artificial methods.The addition of FMLBCs resulted in a reduction of total volatiles in the soil within seven weeks and reached a maximum volatile content in the third week.The addition of FMLBC reduced the exchangeable As components and increased the non-exchangeable As in the soil.The addition of FMLBCs increased soil enzyme activity,indicating that soil humus content increased,soil microbial activity increased,and C and N cycles accelerated;the addition of FMLBCs also changed the relative abundance of bacterial communities,which would affect the process of As methylation and thus As Volatile.（4）The effects of adding FMLBCs on rice and paddy soil were studied through rice pot experiments.The addition of FMLBCs and BC can increase rice biomass and grain weight in arsenic-contaminated soil.Compared with control and BC treatment,FMLBCs effectively reduced As accumulation in different organs of rice.In addition,FMLBCs also reduced the availability of As,increased the amino acid levels in grains,and significantly increased the content of iron and manganese films on the surface of rice roots.The decrease in As accumulation in rice may be attributed to the enhanced adsorption and solidification of As by Fe,Mn,and La oxides,and FMLBCs can provide nutrients and improve the rhizosphere environment to promote rice growth.In addition,the increase of Fe-Mn film on the root surface of rice further hindered the transport of As to rice.The results also showed that with the addition of FMLBCs,the proportion of specifically bound As in soil decreased,and the amount of amorphous hydrated oxides and crystalline hydrated oxides increased.Therefore,FMLBCs change the distribution of As and increase its fixation in soil,which can indirectly reduce the risk of As transfer to rice.The impact mechanism of FMLBCs may include changes in soil physical and chemical properties and soil enzyme activities,which in turn affect the microbial community in the soil,and ultimately affect the morphology and transport of arsenic in the soil.In summary,the application of biochar-metal oxide composite materials can effectively remove arsenic in contaminated water,can reduce arsenic volatilization in soil,and can effectively repair arsenic contaminated soil and reduce the accumulation of arsenic in rice.