Effective Enhancement Of Pyrite On Zero-valent Iron For The Removal Of Arsenic And Imidacloprid From Water

The removal of heavy metals and organic pollutants is a hotspot and a difficult problem in water pollution control.The water treatment technology based on zero-valent iron?Fe⁰?has attracted much attention because it could effectively remove both heavy metals and organic pollutants.Moverover,the technology has the advantages of being cost-effective and environmentally friendly.However,in practical applications,the passivation of pristine oxide film and iron corrosion products that generated during the reaction coated on Fe⁰ surface all could lead Fe⁰ to loss the reactivity.Furthermore,a higher reaction pH also inhibited the removal efficiency of contaminants by Fe⁰.Therefore,the thesis proposed the application of natural pyrite?FeS₂?to modify Fe⁰ and to enhance the reactivity of Fe⁰ for the effective removal of contaminants from water.In this thesis,highly toxic arsenic?As?III??and toxic refractory organic pollutant imidacloprid?IMI?were selected as target pollutants.The study focused on the removal of As by mixed FeS₂-Fe⁰,the removal of As by ball milled FeS₂@Fe⁰ and the degradation of IMI by persulfate?PS?activated by ball milled FeS₂@Fe⁰.The detailed conclusions were concluded:?1?Compared with single-FeS₂ and single-Fe⁰ system,the mixed FeS₂-Fe⁰ system with equal mass had a higher total As removal rate and a faster As?III?oxidation rate at the initial pH range of 3.0-9.0.The optimum mass ratio of mixed FeS₂ and Fe⁰ for effective As removal was 1:1 and the optimum dosage was 2.0 g/L.The variations of Fe²⁺,total Fe²⁺and pH in water,as well as SEM characterization and EPR experiments showed that the corrosion of Fe⁰was improved by the addition of FeS₂,and thereby facilicated the removal of As and the oxidation of As?III?.XPS characterization results revealed that FeS₂-based iron sulfides were produced on the surface of Fe⁰ in the mixed FeS₂-Fe⁰ system.Since FeS₂ owned better electron conductivity and higher standard reduction potential than iron oxides,so they could as a cathode electron conductor to improve the electron transfer of Fe⁰ and promote the corrosion reaction of Fe⁰.?2?Compared with mixed FeS₂-Fe⁰ system,the ball milled FeS₂@Fe⁰ system with equal mass had a higher As removal rate.The total As removal rate in ball milled FeS₂@Fe⁰ system was increased by 21.7 times in comparision to the mixed FeS₂-Fe⁰ system.Results showed that the best mass ratio of ball milled FeS₂ and Fe⁰ for As removal was 1:1,and the optimum dosage was 0.5 g/L.In addition,As removal by ball milled FeS₂@Fe⁰ was quick under acidic condition,while was relatively slow under alkaline condition.The results of SEM-EDS characterizations,determination of total Fe²⁺and electrochemical experiments demonstrated that there were iron sulfides generated on the surface of the Fe⁰.Therefore,ball milled FeS₂@Fe⁰ had a high corrosion reactivity and which facilitated the As removal.?3?Compared with ball milled FeS₂ and ball milled Fe⁰,the ball milled FeS₂@Fe⁰ with equal mass could more effectively activate PS to remove IMI from water.The optimum ball milled mass ratio of FeS₂ and Fe⁰ was 1:9,the optimum dosage was 0.5 g/L,and the optimal loading concentration of PS was 2.5 mmoL/L.Ball milled FeS₂@Fe⁰ could effectively activate PS to remove IMI in a broad pH range of 3.0⁹.0.Based on the results of SEM-EDS and XPS,it was known that FeS₂-based iron sulfides were produced on the surface of Fe⁰ in the ball milled FeS₂@Fe⁰,and the electron density around the surface Fe was increased.These variations probably be the main reason of ball milled FeS₂@Fe⁰ to highly activate PS for the degradation of IMI.In addition,result showed that SO₄^-·was the predominant radical in the system of ball milled FeS₂@Fe⁰/PS/IMI.