Arsenic Pollution Controlling By The Novel Absorbents Based On Mn-Ferrihydrite

Arsenic and its derivatives have a great threat to the environment and biological health.The arsenic pollution in the environment makes the arsenic content of crops higher,such as rice and wheat,which will harm human health.Therefore,reducing the harm of arsenic pollution is a very important task at present.Among the arsenic pollution treatment methods that commonly used,adsorption is considered to have high economic benefits,simple operation,and is the most promising technology.In recent years,manganese-doped ferrihydrite（Mn-Fh）,which combines the function of manganese oxide and ferrihydrite,has attracted attention as an adsorbent for arsenic pollutants due to its good affinity for arsenic.In this study,new materials were prepared based on Mn-Fh to study their structural characteristics,the performance and mechanism of As（III）adsorption.Then Mn-Fh was used as the main raw material to prepare soil amendments,which was applied to pot experiment of rice and wheat and field experiment of rice contaminated with arsenic.The research results are as follows:（1）The adsorption of As（Ⅲ）on manganese-doped ferrihydrite-chitosan beads and its influencing factors were studied.The drying method in the preparation of the absorbent affects its structure and adsorption properties.There are a large number of large pores and mesopores in the freeze-dried beads.The pores of the beads dried under vacuum at 50℃are relatively small,and there is no obvious pore structure in the beads dried naturally at 25℃by air.The orders of the maximum adsorption of As（Ⅲ）and the specific surface area of the beads are the same（Freeze-dried chitosan beads>vacuum-dried chitosan beads>air-dried chitosan beads）.In addition,the adsorption capacity of freeze-dried chitosan beads is twice that of air-dried chitosan beads.As the p H rises,the amount of adsorption gradually decreases;coexistence of anions H₂PO₄^-and Si O₃^2-can significantly inhibit the adsorption capacity of adsorbent for As（Ⅲ）.Furthermore,the adsorption of As（Ⅲ）by freeze-dried chitosan beads conforms to the pseudo second order kinetics equation and Langmuir isotherm model.After regenerations for three times,the adsorption capacity of the material is still about 88%of the original adsorption capacity,which shows the good reusability of chitosan beads.The Mn（IV）in the adsorbent oxidizes As（III）to As（Ⅴ）,which significantly improves the adsorption of As（III）by chitosan beads.（2）The adsorption performance of Mn-Fh@Zr（OH）₄powder was studied.The material with Zr:Mn:Fe ratio of 1:2:4 was mixed with chitosan to prepare Mn-Fh@Zr（OH）₄-Cs material.And the adsorption of As（III）by the beads meets the pseudo second order kinetic equation and the Langmuir isotherm model.In addition,the maximum adsorption amount is about 48mg/g.The adsorption of As（III）on the beads is mainly monomolecular layer chemical adsorption.And the loading of zirconium hydroxide makes the hydrolysis reaction easier to happen on the surface of the material,which ionizes the hydroxyl sites,accelerates the adsorption of As（III）,and shortens the time for adsorption to reach equilibrium.（3）The effect of Mn-Fh soil amendments on arsenic in soil and crops was studied.In the experiment of potting rice and wheat with arsenic contaminated soil,the application of a small amount of Mn-Fh soil amendments can significantly reduce the concentration of available arsenic.The concentration of available arsenic in rice and wheat potting soil was reduced by 30%and 80%respectively.And the arsenic content in the roots,stems,leaves and seeds of potted rice samples decreased by 60%,55%,58%and 60%respectively.In addition,the arsenic content of stems,leaves and seeds of potted wheat plants decreased by 85%,85%and 86%respectively.The available arsenic concentration in the soil was reduced by up to 35%and 28%respectively with applying Mn-Fh soil amendments to arsenic-contaminated fields and plots.Furthermore,the arsenic content of rice seeds in the field was reduced by up to 43%,and the arsenic content in roots,stems,leaves and seeds of rice in the plots was reduced by up to 43%,45%,51%and 40%.The application of a small amount of Mn-Fh soil amendments does not affect the content of Mn and Fe in the soil,which means it is a safe and effective soil improver amendments.