Abstract: The effects of sulfate on transformation and release of iron and arsenate in the soil contaminated by acid mine drainage were investigated by means of flooding release experiment in this study. Three kinds of comparative tests were designed and conducted, including sterilization treatment, non-sterilization treatment and sulfation non-sterilization treatment. Each treatment was incubated for 30 days in an anaerobic incubation box, and the supernatants of each treatment were sampled every 5 days, to determine pH values, redox potential (Eh), and ferrous iron and arsenic concentrations. The HCl-extractable Fe(Ⅱ) and arsenic concentrations in the soil were also determined. In the initial stage, pH in soil solution increased, yet Eh decreased with the help of soil microorganisms. In the first 5 days (stage of reduction and transformation of iron minerals), the activation rate of iron and arsenic in the soil and the release rate were higher than comparative treatment, and the addition of sulfate would increase the rate of release. After then, a large amount of sulfate was reduced and ferrous sulfide minerals were formed due to the enhancement of reduction strength in soil. The reduction rate of iron oxides in the soil was kept at a lower level, except for sulfurization non-sterilization treatment, and the content of activated arsenic in the soil decreased. The process of iron and arsenic release was suppressed. The iron concentration in the solution was maintained at a lower level after 15 days of the experiment, which was probably resulted by the formation of iron oxides deposits. However, the arsenic concentration increased gradually and the addition of sulfate could enhance the release of arsenic.

Key words: soil microorganism, sulfate, iron, arsenic