Thallium,a heavy mental element,whose toxicity is stronger than those of mercury and cadmium,has been listed as one of the heavy mental pollutants requiring intensive prevention and control by National 12th Five-Year Plan For Comprehensive Prevention and Control of heavy mental pollutants.Phase thallium in pyrite was analyzed by inductively coupled plasma mass spectrum(ICP-MS)with sequential extraction procedure.The results showed that thallium of pyrite existed mostly in silicate phase and mineral structure by acid-exchangeable state and the proportion were 58%and 25%respectively.Thallium existed less in pyrite(FeS2)by oxidable state with 11%,and least in iron oxides by reducible state with 6%.The release and migration behaviors of thallium in pyrite were mainly derived from acid-exchangeable and oxidable state thallium at natural environment.The surface reaction in pyrite was investigated by the diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS),and it was found that the surface hydroxyls in pyrite were strengthened in the process of surface oxidation but reduced obviously in the process of treating acidic solution containing thallium.Acidic liquid membrane formed by obvious surface dissolution and neutralization of this acidity by the carbonate in pyrite were further indicated by the attenuated total reflection(ATR).It was propounded that the neutralization from carbonate greatly influenced the release of thallium from pyrite through the experiment of pyrite treating acidic solution containing thallium.A thallium release mechanism was proposed that the dissolution-adsorption precipitation equilibrium was occurred,and the equilibrium was under the control of both neutralization reaction of carbonate and surface oxidation of pyrite,and finally decided the release and migration of thallium.