Preparation Of Sulfied Zero-valent Iron Using Limonite And Used As Persulfate Activator For Removing Atrazine

Activated persulfate processes is a novel advance oxidation processes that used sulfate radical（SO₄.^-）as the main active radical to remove pollutants.The activation of PS using sulfidated zero valent iron（S-ZVI）has gained much attention.At present,S-ZVI is mainly prepared using sodium borohydride,vulcanizing agent and Fe³⁺/Fe²⁺solution by reduction method or zero valent iron（ZVI）and S through ball milling technology.The main problems of these preparation methods are cumbersome steps and high preparation costs.The aim of this dissertation is to prepare S-ZVI by carbothermic reduction technology using cheap limonite and pyrite as raw materials and use S-ZVI to activate PS for the elimination of atrazine（ATZ）in water.The major research contents and conclusions are as follows:The mechanism of S-ZVI preparation of limonite and pyrite using carbothermal reduction was studied.The results showed that preparation of S-ZVI of limonite and pyrite using carbothermal reduction is theoretically feasible.The reduction process of limonite is Fe O（OH）→Fe₂O₃→Fe₃O₄→Fe O→Fe;pyrite（Fe S₂）is gradually decomposed into S vapor and Fe S according to:Fe S₂→Fe_1-xS+S→Fe S+S at high temperature;Fe reacts with S vapor to form Fe_1-xS.The influence of pyrite dosage,roasting temperature and roasting time on the degradation of ATZ by S-ZVI activated PS were studied.The results showed that the degradation efficiency of ATZ increased significantly with the increase of pyrite dosage,roasting temperature or roasting time.The optimum roasting conditions are as follows:the amount of pyrite was 4%,the roasting temperature was 1000℃and the roasting time was 60 min.The phase transformation and microstructure of limonite during carbothermic reduction was studied using X-ray diffraction,scanning electron microscope and energy dispersive spectrometer.Meanwhile,the changes of iron metallization rate,the content of total iron and S of roasted products under different roasting conditions were determined.The results showed that Fe_1-xS can be formed by the introduction of pyrite,which covers the surface of ZVI at the micro-nano level,forming S-ZVI with core-shell structure,and Si O₂ in limonite was the S-ZVI carrier.Increasing the roasting temperature and prolonging the roasting time was beneficial to the reduction of iron minerals and the formation of Fe_1-xS,while the high roasting temperature also lead to the growth of S-ZVI particles.The efficiency of S-ZVI@Si O₂ to activate PS to degrade ATZ was studied.The results showed that the removal rate of ATZ in the S-ZVI@Si O₂/PS system increased with the increase of the dosage of S-ZVI@Si O₂ and PS.Compared with the ZVI@Si O₂/PS system,the degradation rate of ATZ was faster in S-ZVI@Si O₂/PS system,and the S-ZVI@Si O₂/PS system was suitable for a wider p H range.At the high concentration of ATZ（15 mg/L）,the final degradation rate of ATZ could also reach about 70%.The higher the solution temperature,the more favorable degradation of ATZ.The concentration of inorganic anions selected in this experiment was 1-10 m M,Cl^-could accelerate the degradation of ATZ in the S-ZVI@Si O₂/PS system,CO₃^2-inhibited the degradation of ATZ,and NO₃^-had little effect on the degradation of ATZ in this system.When the concentration of FA was low（1 mg/L）,FA had little effect on the degradation of ATZ in the system.When the concentration of FA increased to 5 mg/L and above,the degradation of ATZ was significantly inhibited.The prepared S-ZVI@Si O₂ had the ability of continuously activating PS to degrade organic pollutants and could be reused.The quenching test and electron spin resonance test proved that SO₄.^-and HO.were the primary reactive radical in the S-ZVI@Si O₂/PS system,and SO₄.^-was the main radical species.Fe_1-xS in the S-ZVI@Si O₂/PS system contributed greatly to the dissolution of Fe²⁺.The degradation products of ATZ were detected by liquid chromatography-mass spectrometry（LC-MS）,and the possible reaction pathways of ATZ including dealkylation,alkyl oxidation and deoxy-hydroxylation.The S-ZVI@Si O₂/PS system could oxidatively degrade ATZ macromolecules into small molecules,however,had poor mineralization effect on ATZ.