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Antimony(Sb)has been included as priority pollutants by Environmental Protection Agency of the United States and the Council of the European Communities due to its toxicity to human health.The toxicity and mobility of Sb depends on its oxidation state,in oxic environment,Sb(Ⅴ)is the predominant species and exist as Sb(OH)6?,whereas under anoxic waters,Sb(Ⅲ)mainly occurs as Sb(OH)3 and is more stable and toxic.However,the geochemical fate of Sb remained largely unexplored.Pyrite(FeS2)is the most abundant natural sulfur mineral on the earths surface and is also a associated mineral of stibnite.The prior study reported the formation of hydroxyl radical(OH?)and H2O2 upon addition of pyrite to O2-free water.The formed H2O2 and OH? By pyrite may influence the fate of Sb(Ⅲ)in the environment.The objective of this study was to understand the oxidation mechanism of Sb(Ⅲ)by pyrite.The pyrite was crushed and passed through 200 mesh sieve.250 mL of 0.25g/L pyrite suspensions were placed on a shaker at 180rpm and 25±0.1?C.About 1 mL of solution was taken and filtered through 0.22μm cellulose filters at selected time intervals.The filtered solution was immediately analyzed for separation of Sb(Ⅲ)and Sb(Ⅴ).The photooxidation experiments were conducted by a photochemical reactor,a 500 W Xe lamp(λ>400 nm)was used as simulated sunlight source.The rapid photooxidation of Sb(Ⅲ)by pyrite occurred in a wide range of pH.The reaction efficiency was significantly affected by the pH of the solution,under oxic conditions,as the pH ranged from acid to alkaline,the rate of oxidation reaction was gradually fast.The oxidation of Sb(Ⅲ)to Sb(Ⅴ)by OH.and H2O2 formed by pyrite occurred whereas the H2O2 was the main oxidant in this system.Under anoxic conditions,the relative lower efficiency of Sb(Ⅲ)oxidation rate was observed.The oxidation of pyrite by O2 can also contribute a certain proportion of the OH.and H2O2.The photooxidation of Sb(Ⅲ)by pyrite was remarkably fast as the pyrite is a semiconductor,illumination of pyrite by visible light will force the hole to migrate to the interface and to react with water to produce OH..