The Mechanisms Of Biochar Mediated Fe/as Migration And Transformation

Biochar,which is rich in redox functional groups,can mediate the reduction and dissolution of iron minerals and the migration and transformation of arsenic adsorbed on its surface in the form of electron shuttle or electron donor under the drive of microorganisms.The types and contents of functional groups from different biochar sources are also different,leading to the differences in iron/arsenic migration and transformation mechanisms mediated by biochar sources.In this study,a system that simulates the occurrence of arsenic in the natural environment was constructed,rice husk biochar(BCD)and hemp biochar(BCM)were selected,arsenic-containing goethite and arsenic-containing hematite were prepared,and biochar-mediated iron/arsenic was developed.Research on the mechanism of migration and transformation reveals the different mechanisms of iron/arsenic migration and transformation of different sources of biochar under different influencing factors,in order to better understand the potential accumulation of different sources of biochar mediated iron/arsenic biogeochemical cycle the basic information.The paper draws the following conclusions:1.The Fe/As concentration or the amount of electrons in the group with added biochar were higher than those of the group without biochar,indicating that the presence of biochar can significantly promote the reduction of arsenic-bearing iron ores.Among them,in the process of Fe/As reduction by biochar coupled with dissimilar iron-reducing bacteria(MR-1),the promotion of Fe/As reduction release by biochar acting as an electron shuttle is more significant than that by biochar acting as an electron donor.2.The determination of electron gain and loss capacity of dissolved organic matter(DOM)from biochar showed that both kinds of biochar had electron accepting(EAC)and electron donating ability(EDC),and rice husk biochar(BCD)had better electron accepting ability and electron donating ability than hemp stem biochar(BCM).It is further proved that biochar has the characteristics of electron shuttle.3.The effect of biochar coupling MR-1 from different sources on the reduction release of Fe/As is different.Both as an electron shuttle and electron donor,the number of electrons obtained from Fe/As in the system with BCD participation was higher than that of BCM.At the same time,in the abiotic group,the reduction and release rules of Fe/As in the biological group were basically the same as those in the BCM group,indicating that BCD mediated the reduction and release of Fe/As in the biological group was stronger than BCM.4.Comparison of biochar mediated reduction dissolution of different types of arsenic-bearing iron ores shows that the reduction release level of iron/arsenic in arsenic-bearing goethite system is higher than that in arsenic-bearing hematite group.This is because the larger specific surface area of goethite makes the contact area with the dissimilated iron-reducing bacteria larger,and the mineral morphology is regular and the degree of crystallization is low,so it is easier to be reduced.5.Through correlation analysis,it is found that the hydroxyl functional group,fatty family functional group and carboxyl functional group are the main functional groups,and are negatively correlated with the concentration of ferrous and trivalent arsenic,indicating that the above three functional groups are the key groups of biochar in the process of iron/arsenic reduction and conversion.