Application Of Polyethyleneimine Stabilized Nanoscale Zero-valent Iron-magnetite（Fe₃O₄@nZVI-PEI） For The Enhanced Removal Of Arsenic From Acidic Wastewater

Arsenic pollution in water bodies has become a problem in the world and urgently needs to be resolved as it poses a serious threat to the environment and humans.As a large industrial country,China produces large amounts of acidic arsenic-containing wastewater in the process of smelting non-ferrous metals,especially in the industrial metal smelting process where the wet purification process is used for acid production,leading to the increasing concentration of arsenic in water sources.Studies have shown that long-term exposure to arsenic-contaminated water can lead to serious health implications,from mild diarrhea to severe kidney and skin cancer and even death.As such,the World Health Organization（WHO）has set a discharge standard for arsenic-containing wastewater at a concentration lower than 0.01 mg/L.The application of the adsorption technique has been widely reported in the field of water treatment due to its advantages of easy operation,low cost,and low energy consumption.It is the most widely used method for the removal of arsenic contamination in water,especially for water bodies with large treatment requirements and low arsenic concentrations.In recent years,the use of nanoscale zero-valent iron（n ZVI）has become an effective technology for the purification of acidic arsenic-containing wastewater due to its strong reducing ability,high specific surface area,reaction rate,and excellent affinity for arsenic species.However,the rapid and severe agglomeration of n ZVI limits its practical application.Therefore,in this study,Fe₃O₄ was used as a substrate material and n ZVI was uniformly loaded onto it by liquid-phase in situ reductions to obtain n ZVI-Fe₃O₄ dual nanosystem.Subsequently,a new iron-based material（Fe₃O₄@n ZVI-PEI）rich in amino functional groups was synthesized by further surface modification with polyethyleneimine（PEI）and used for the treatment of acidic arsenic-containing wastewater.The characterization and analysis of Fe₃O₄@n ZVI-PEI showed that using Fe₃O₄ as substate material enhanced the dispersion of n ZVI,solved the agglomeration problem,and further improved its reactivity,thus achieving high arsenic removal capacity.Surface modification with PEI also increases stability,prevents the rapid oxidation of n ZVI,and introduces large ammonium functional groups to increase the adsorption sites and thus,improve the adsorption capacity.The results of the adsorption experiments showed that Fe₃O₄@n ZVI-PEI achieved high removal efficiency for As（III/V）at p H～3.0 and the adsorption kinetics was per the pseudo-second model,indicating that the adsorption process was mainly chemisorption.The thermodynamic study followed Sip’s model and the adsorption capacity reached 835.66 mg/g for As（III）and 1518.93 mg/g for As（V）.The effect of coexisting anions in the wastewater on the adsorption capacity of the material was investigated by considering the actual situation of acidic arsenic-containing wastewater,and the results showed that the coexisting ions had almost no effect on the adsorption of arsenic at a solution p H of 3.0.In contrast to Cl^-,NO₃^-and SO₄^2-,PO₄^3-had a strong effect on the adsorption capacity.The material showed good arsenic removal performance after four cycles.Finally,the adsorption mechanism of Fe₃O₄@n ZVI-PEI on As（III/V）was investigated and the results revealed that the possible removal mechanisms involve are electrostatic interaction,redox reactions and surface complexation.Overall,the iron-based material（Fe₃O₄@n ZVI-PEI）synthesized in this study has some potential applications in the remediation of acidic arsenic-containing wastewater.29 Figures,7 Tables,154 References...