Effects Of Biochar On Arsenic Release In Paddy Soil Contaminated By Acid Mine Drainag

In recent years,the problem of heavy metal pollution has risen sharply in the field of environmental protection.Arsenic(As)pollution is seriously threatening people’s health and life safety.Because of its high porosity,high specific surface area and rich organic functional groups,biochar is widely used as an environmentally friendly alkaline additive in the treatment of heavy metal pollution in soil.However,the structure of biochar prepared at different temperatures is different,and the effect on the availability and migration of As in soil is different;At the same time,the application amount of biochar is also closely related to the transformation of As in soil.In this study,Eupatorium adenophorum was used as biomass raw material,which was pyrolysed at 400 ℃,550 ℃ and 700 ℃ respectively,and the prepared biochar was added to the paddy soil polluted by acid mine wastewater in different proportions(1% and 3%).Through controlling the oxidation and reduction conditions,the process of flooding and drying of rice planting soil was simulated to study the release,migration and form transformation of soil As under the conditions of adding biochar,It is also explored that biomass carbon affects the adsorption and distribution of As by affecting the oxidation-reduction process of iron oxide in soil.The main experimental results are as follows:(1)Different preparation temperatures and different amounts of biochar have different effects on the physicochemical properties and microbial community structure of paddy soil.Under anaerobic conditions,the soil p H,Eh value and DOC content of the experimental group were lower,and the abundance of As/Fe reducing bacteria was higher;There was a positive correlation between the preparation temperature of biochar and soil p H and DOC content.However,under aerobic conditions,the soil p H of the experimental group was lower,and the Eh value,DOC content and the abundance of Fe-oxidizing bacteria were higher;There was a negative correlation between the preparation temperature of biochar and soil p H and DOC content.The soil Eh value and DOC content are mainly controlled by the amount of biomass carbon added.(2)Under anaerobic conditions,compared with the control group,the addition of biochar increased the concentration of Fe(II)in the solution.As adsorbed on the surface of iron oxide was released into the solution,and the amount of As released was positively correlated with the amount of biochar added.Meanwhile,the residual As concentration in soil was mainly controlled by the amount of biochar added.The higher the amount of biochar added,the lower the residual As concentration,indicating a higher migration and bioavailability of As.Under aerobic conditions,the Fe(II)and As concentrations in soil solution were relatively low.As gradually transformed into amorphous iron and aluminum oxides and crystalline iron and aluminum oxides,indicating that under aerobic conditions,more iron oxides adsorbed As through adsorption and co-precipitation and then deposited into the soil or loaded onto the surface of biochar.Under anaerobic-aerobic conditions,the iron oxides underwent reduction-oxidation,causing the adsorption-desorption of As on the surface of biochar.(3)After consecutive experiments,a comparative analysis was conducted on the surface As and Fe content,binding mode,functional group type,and mineral composition of biomass char using SEM-EDS analysis,FTIR analysis,XRD analysis,and XPS analysis.The results showed that the higher the preparation temperature of biomass char(BC-400,BC-550,BC-700),the stronger its adsorption capacity for Fe(11%,14%,26%).The As and Fe content of biomass char(BC-700)increased and exhibited a positive correlation.The newly generated Fe-O functional group on its surface formed a complex with As,and the crystal transformed into the relatively stable mineral,scorodite(Fe As O).There was no significant change in the functional group type on the surfaces of BC-400 and BC-550.