Study On The Removal Performance And Mechanism Of Aquatic Sb(Ⅲ) By Sulfidated Nanoscrale Zero-valent Iron

Recently,pollution of Sb（Ⅲ）in water has caused great concern,posing a serious threat to the environment and human health.Techniques such as adsorption,coagulation/flocculation,electrochemistry and ion exchange has been applied for Antimony removal.Among,the adsorption method is used due to its low cost and high processing efficiency.As an adsorbent,iron oxide has the advantages of easy-production,non-toxicity,eco-friendliness,and strong affinity for Sb（Ⅲ）/Sb（Ⅴ）.Nanoscale zero-valent iron（nZVI）,sustainable generating fresh iron oxyhydroxide from its corrosion,is a promising iron-based adsorption material.However,rapid passivation and low adsorption capacity limit its practical application.Hence,this study provides a new and efficient nanotechnology to remove Sb（Ⅲ）using the sulfidated nanoscale zero-valent iron（S-nZVI）.S-nZVI is prepared by depositing Fe S on the surface of nZVI by the precipitation reaction of Fe²⁺and S^2-.Characterized by XPS and XRD,the surface composition of S-nZVI is Fe S and Fe S₂,with the better crystallinity than nZVI.Comparing the Sb（Ⅲ）removal process of S-nZVI and nZVI,the reactivity of S-nZVI is stronger than nZVI.Within 2 h aerobic reaction,the removal rate by S-nZVI is up to 96.5%,while nZVI can only remove 77.8%of Sb（Ⅲ）.Under anoxic condition,S-nZVI removed 64.3%of Sb（Ⅲ）,while nZVI only removed 44.5%of Sb（Ⅲ）.The calculated Sb（Ⅴ）accumulation rate（k）（0.23 mg/L·min）of S-nZVI is 2.3 times higher than that of nZVI（0.10 mg/L·min）,indicating that the ability of S-nZVI to oxidize Sb（Ⅲ）is higher than nZVI.Under anoxic condition,Sb（Ⅲ）is adsorbed and fixed on S-nZVI or nZVI,which indicated that the adsorption capacity of S-nZVI is higher than nZVI.The adaptability of S-nZVI to environmental conditions was studied by the experiments on the effects of different concentrations,pH and coexisting ions.The maximum adsorption capacity of S-nZVI reaches 465.1 mg/g,which is much higher than 83.3 mg/g of nZVI,indicating S-nZVI can effectively remove high-concentration Sb（Ⅲ）.The results of adsorption kinetics and adsorption isotherms indicate that chemical adsorption dominates the adsorption process when S-nZVI is treated at low concentration of Sb（Ⅲ）,and physical adsorption leads the removal of high concentration of Sb（Ⅲ）.pH has little effect on the removal of Sb（Ⅲ）by S-nZVI,which maintains the high-efficiency removal of Sb（Ⅲ）in 4.0-9.0.Acidic conditions are more conducive to the oxidation of Sb（Ⅲ）and so accelerate the removal rate of Sb（Ⅲ）.Coexisting ions have a negative effect on S-nZVI removal of Sb（Ⅲ）,which can be ordered by Cl^-<NO₃^-<Si O₄^4-<CO₃^2-<PO₄^3-.The surface Fe S content was studied in the S-nZVI reaction system under aerobic or anoxic condition,in the absence or presence of 1,10-phenanthroline.The higher the Fe S/Fe⁰ratio,the higher the reactivity of S-nZVI.During the aerobic reaction,both Fe²⁺and S^2-play the important roles on the removal of Sb（Ⅲ）by catalyzing the production of·OH.In addition,S^2-can increase the efficiency of Fenton reaction by accelerating the circulation of Fe³⁺/Fe²⁺to increase the Sb（Ⅲ）removal capacity by S-nZVI.Two quenchers Me OH and TBA was used to determine the exist of·OH and SO₄·^-,based on their different reaction rate with·OH and SO₄·^-.It was preliminarily concluded that both·OH are produced in the reaction system,and·OH plays an important role in oxidation process.The mechanism of Sb（Ⅲ）removal by S-nZVI under aerobic conditions includes adsorption,oxidation,and co-precipitation.Among them,oxidation has a great influence on the removal rate of Sb（Ⅲ）,accounting for about 78%of removal rate.The XPS analysis of Sb（Ⅲ）-treated S-nZVI showed that the contents of Sb（Ⅲ）and Sb（Ⅴ）were 47.6%and 52.4%,respectively,which again indicated that oxidation played a major role in the removal of Sb（Ⅲ）.