Transport Of Ferrihydrite Nanoparticles In Soils And Its Effect On Arsenic Chemical Behavior

Arsenic(As)is a toxic metalloid pollutant ubiquitous in the environment,which seriously threatens human health.Ferrihydrite nanoparticle has the advantages of small particle,large specific surface area,high reactivity,poor crystallinity and surface structural defects,and has great sorption and immobilization ability for arsenic.However,there is few research about the stability and transport behavior of nano-ferrihydrite in soil.In addition,the effect of the whole process on the immobilization and fate of arsenic in soil is uncertain.In this study,12 typical soils with different physical and chemical properties were selected as environmental media.First,the dispersion stability of nano-ferrihydrite suspensions in soil was studied through batch experiments;Then,the transport behavior and influencing factors of ferrihydrite nanoparticles in saturated soil medium were explored through soil column experiments,and the longest transport distance was calculated.Finally,three representative soils were selected to prepare arsenic polluted soil,and the effect of nano-ferrihydrite on the chemical behavior of arsenic was studied through soil column leaching experiments.This study provides data reference and theoretical basis for the environmental behavior of nanometer materials in soil and their in situ remediation of arsenic pollution in soil.The main experimental results as follows:1.Using sodium carboxymethyl cellulose as a stabilizer to synthesize ferrihydrite nanometer materials in the laboratory,the hydration radius is 149 nm,which is smaller than the hydration radius of ferrihydrite and has better stability and dispersibility.After standing for 20 days,nano-ferrihydrite showed good suspension and dispersion in cinnamon soil,granite latosol,black soil,and irrigated desert soil.Among them,the hydration radius and Zeta potential of the granite latosol had little change,the hydration radius of the suspension was499.5 nm,and the Zeta potential value was-24.53 m V.In purple sandshale and purplish soil with less organic matter content,the hydration radius of the suspension increases significantly,the Zeta potential is less electronegative,and the stability is poor.2.In fluvo-aquic soil,cinnamon soil,brown soil,latosol and acid red soil,the transport plateau relative concentration of nano-ferrihydrite more than 0.5,showing strong mobility.However,the transport ability in purple sandshale,black soil,irrigated desert soil and purplish soil is poor,the transport plateau relative concentrationis less than 0.4.The transport plateau relative concentration in acidic soil was mainly negatively correlated with cation exchange capacity,and in alkaline soil was negatively correlated with clay content.The distribution of amorphous iron oxide content in the soil is related to the transport properties of nano-ferrihydrite.In all soils,nano-ferrihydrite has a long transport distance in acidic soils such as latosol and red soil,and the transport distance was predicted to be between 216.64 and 258.47 cm.3.Three kinds of soils,namely fluvo-aquic soil,cinnamon soil,and basalt-latosol,were selected to prepare arsenic polluted soil,which was aged for60 days.The available arsenic content was 21.0,17.1,and 1.2 mg/kg,respectively.Compared with unpolluted arsenic soil,the transport plateau relative concentration of nano-ferrihydrite in fluvo-aquic soil and cinnamon soil was significantly lower,and the content of amorphous iron oxide in soil column was significantly higher,mainly distributed in the upper end of soil column.The nano-ferrihydrite can still maintain a good transport ability in the basalt-latosol.The results of the arsenic breakthrough curve showed that the nano-ferrihydrite inhibited the transport of arsenic in fluvo-aquic soil,but promoted the transport of arsenic in cinnamon soil,which may be co-transport of nano-ferrihydrite and arsenic.The content of available arsenic in basalt-latosol is very low,and the content of arsenic in the effluent is also very low.The maximum transport distance of nano-ferrihydrite in the three polluted soils was greater than 30.00 cm,and fluvo-aquic soil and basalt-latosol were much smaller than those in unpolluted soil.