| As a typical soil metal pollutant,arsenic（As）poses a potential threat to the ecological environment and human health.Passivation remediation technology is currently the main method of remediation of farmland As pollution,of which iron-based materials are mainly commonly used passivation materials.However,our research found that the use of different iron-based materials to passivate arsenic in farmland soil will promote the dissolution of manganese.Although manganese is one of the essential trace elements of crops,excessive manganese will cause toxicity to crops.Therefore,research Iron-based materials are necessary for the passivation of arsenic in farmland soil and the mechanism of manganese dissolution.In this study,paddy soil contaminated with arsenic was used as the research object,and iron-based materials such as iron fulvic acid（HFS）and ferrihydrite（STK）were used as passivation materials for As.Through indoor soil culture experiments,conventional chemical analysis methods were used.The effects of iron-based materials on p H,effective As,effective Fe and effective Mn in the soil were investigated with XRD,FT-IR and XPS for in-depth analysis to study the phase change of Mn and the change of valence state in the soil,Preliminary discussion of the mechanism of Mn dissolution during the passivation of As in iron-based materials.The main findings are as follows:（1）Both iron-based materials（STK and HFS）significantly reduced the content of available As in the soil.The passivation effect is most obvious at 45days.The addition of HFS reduced the effective As content by 40%,from the original 1.81 mg·kg-1to 1.06 mg·kg-1.The addition of STK reduced the effective As 20%,reduced from the original 1.81 mg·kg-1to 1.46 mg·kg-1.（2）Both iron-based materials increase the effective Mn content in the soil.Among them,the content of effective Mn in the soil added with HFS increased significantly,but the effective Mn in STK did not increase significantly.Among them,at 45 days,the effective state Mn of the HFS treatment group was the highest,increased from the original 1.43 mg·kg-1to 125.3 mg·kg-1,an 86-fold increase over CK;while the STK treatment was from the original 1.43 mg·kg-1increased to 2.37 mg·kg-1,an increase of 64%.（3）The decrease of soil p H value is the key factor leading to the dissolution of effective Mn.The experimental results show that under acidic conditions,the effective Mn is up to 1.4 times higher than the control.According to XRD and XPS pattern analysis,after adding iron-based materials,the content of Mn（II）and Mn（III）in the soil of the HFS treatment group increased,which the main reasons for this phenomenon are the following:1.The decrease in p H.2.Fe ions in humic acid-iron complex（HA-Fe）and fulvic acid-iron complex（FA-Fe）in HFS and the mineral structure and As（III）occurrence of manganese-arsenic conjugate（Mn-As）in soil The redox reaction and the lattice replacement reaction release free Fe ions,thereby destroying the dynamic equilibrium system between the free iron-manganese conjugates（Fe-Mn）in the original soil,making the stable Mn ions in the original soil.Thus it changes to the effective state,which causes the dissolution of Mn. |
