| Arsenic(As)is a toxic metal-like element that is naturally enriched in soil or sediment and can be dissolved or desorbed into water under special circumstances.Low concentrations over time can accumulate in the body and have serious health effects.Arsenic pollution has become a global concern of environmental pollution,the study of the migration and transformation of arsenic in the natural environment and the control of arsenic pollution has become more and more important.Iron(Fe)in the environment has an important effect on the complexation behavior of natural organic(Natural Organic Matter)matter and As.It is particularly important to study the effect of Fe on As complexation of humic acid(Humic Acid,HA)so As to master the migration and transformation of As in the environment.In this thesis,HA represents natural organic matter and Fe represents metal bridge ion.The physical and chemical properties of HA were further studied by means of Ultraviolet spectrum,infrared spectrum,atomic fluorescence,total organic carbon content and particle size distribution.The effects of Fe（Ⅱ）and Fe（Ⅲ）on the complexation of As(V),As(III)and HA with different molecular weight components were studied by equilibrium dialysis and ultrafiltration under environmental p H,DOC concentration,initial arsenic concentration and molecular weight.The main results are as follows:(1)The physicochemical properties of different molecular weight components in HA were different.DOC content decreased with decreasing molecular weight,and the DOC content of HA component without ultrafiltration was between UF2 and UF3.The degree of humification decreased with the decrease of molecular weight.The infrared spectrum characteristics of HA with different molecular weights are similar,but there are some differences in peak intensity and position.Humic acid particle size range is mainly 50-150 nm.(2)As(V)/As(III)dynamic dialysis experiments show that both As(V)and As(III)can directly complex with HA,and the interaction time of As(V)and As(III)with HA can reach the complex equilibrium at about 200 hours and 130 hours,respectively.(3)Both Fe（Ⅱ）and Fe（Ⅲ）can enhance the complexation ability of HA As,and the enhancement effect of HA on the complexation ability of As(V)is greater than that of As(III).PH significantly affected the ability of HA complexing arsenic,and the complexing percentage of As(III)and HA decreased with the increase of p H.The maximum amount of As(III)complexed with Fe（Ⅱ）-HA at p H 7;The maximum amount of As(III)complexed with Fe（Ⅲ）-HA at p H 9.(4)As the concentration of dissolved organic carbon(DOC)increases,the proportion of complex As interacting with HA containing Fe（Ⅱ）/Fe（Ⅲ）increases.When the initial Concentration of As increases from 100 μg/L to 1000 μg/L,the complexation percentage of HA,HA-Fe（Ⅱ）and HA-Fe（Ⅲ）decreases As(V)/As(III).(5)Molecular weight greater >100 k Da,the percentage of As was the highest,and the percentage of Arsenic in HA with molecular weight less than 10 k Da was significantly higher than that in other molecular weights.The complexation ability of HA with As(V)was higher than that of As(III).The enhancement effect of Fe mainly results from the formation of a bridge between Fe and carboxyl group and the formation of ternary complex with As.The colloid with particle size between 300-400 nm,and the particle size of Fe（Ⅲ）-HA-As complex is larger than that of Fe（Ⅱ）-HA-As..In conclusion,different p H values,DOC concentration,As concentration and different molecular weights in the environment will affect the complexation of Fe（Ⅱ）/Fe（Ⅲ）to humic acid and As(V),mainly due to the functional groups and the forms of arsenic in humic acid through mechanism analysis.These results can be used as a reference to clarify the mechanism of natural organic matter and arsenic in peatland,wetland or floodplain sediments with high organic matter and iron content,and to predict the risk of arsenic pollution in water sediments. |
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