| Arsenic pollution incidents occur frequently,the exploration of efficient and reasonable arsenic pollution remediation technology has gradually become a research hotspot.Adsorption method is the most commonly used technique for arsenic remediation due to its advantages of simplicity,high efficiency and low cost.Fe-Mn binary oxides（FMBO）,as an efficient arsenic removal adsorbent,has been widely used in arsenic pollution remediation.However,its application in practical engineering is limited by defects such as small,difficult to separate and easy to aggregate.Calcined oyster shell（OS）with large specific surface area and rich pore structure was used as the carrier of FMBO,Fe-Mn binary oxide/oyster shell（FMBO/OS）adsorbent was prepared by hydrothermal co-precipitation method for the adsorption of aqueous As（Ⅲ）.The performance of FMBO/OS adsorbent was evaluated from the aspects of adsorption capacity,cyclic regeneration and material stability.The effects of synthetic ratio,pH of initial solution and competitive ions on the arsenic removal efficiency of the adsorbent were investigated,and the arsenic removal mechanism was also discussed.The morphology,structure and chemical composition of FMBO/OS were analyzed by various characterization methods.It was found that iron oxides and manganese oxides in the composite system were loaded on the surface of oyster shell in the form of Fe2O3,Fe OOH and Mn O2,Mn OOH.FMBO had good dispersibility on the carrier,which laid a good foundation for the adsorption of As（Ⅲ）.Through the optimization experiment of adsorbent synthesis ratio,it was found that the FMBO/OS with FMBO load ratio of 50%and Fe:Mn mole ratio of 3:1 had the best adsorption efficiency on As（Ⅲ）,and the adsorption amount was about twice that of FMBO.The adsorption of As（Ⅲ）by FMBO/OS adsorbent increased rapidly in the first 3 h,then slowed down gradually and stabilized after 12 h.The adsorption equilibrium was reached within 24 h,and the removal efficiency reached 95%（The initial concentration of As（Ⅲ）solution:C0=10 mg/L,pH=5.0,25°C）.The adsorption process conformed to the pseudo-second-order kinetic model and Freundlich isothermal adsorption model,which indicated that chemical adsorption occurred in the adsorption process,and the adsorption is exothermic process.The FMBO/OS had a great pH-dependence on the removal of As（Ⅲ）,and the adsorption efficiency was the best when pH=5.0.In addition,the adsorbent had good selectivity and reusability.The changes of valence state and morphology of Fe/Mn,functional group and composition in the adsorbent before and after As（Ⅲ）adsorption showed that Mn O2 oxidized As（Ⅲ）to As（V）,and iron oxide played an important role on As（V）adsorption in this composite system.As the carrier of FMBO,porous calcined oyster shells could not only effectively alleviate the agglomeration phenomenon of FMBO,but also reacted with As（V）to produce calcium arsenate precipitation,which further improved the arsenic removal efficiency of the adsorbent.On this basis,in order to further improve the particle size and material stability of FMBO/OS adsorbent,sodium alginate hydrogel was used to encapsulate the adsorbent,which increased the particle size of the adsorbent and effectively reduced the activity loss of FMBO/OS.The leaching efficiencies of manganese ion decreased from 9.1%,7.7%and 13%to 2.5%,2.6%and 2.2%（C0=10/100/150 mg/L,t=24 h）,which improved the chemical stability of the adsorbent.This work provides a new idea for the synthesis of efficient and green arsenic removal adsorbent.Besides,it provides a reference for the reuse of waste biomass materials such as oyster shells. |
