Experimental Study On Oxidation Of Pyrite Mediated By Acidophilic Bacteria

Pyrite is one of the most abundant sulfide minerals in curst. Heavy metal elements can be released during the oxidation of pyrite, together with the formation of acid mine drainage (AMD), which causes serious environment pollution. Numerous researches have been carried out on the bioleaching process of sulfide minerals. However, the mechanism and kinetics of pyrite bioleaching is still a disputable subject.Three species of acidophilic bacteria isolated from acid mine drainage were studied in this thesis, namely Acidithiobacillus ferrooxidans (iron-oxidation bacteria), NJU-AMDS2(iron-oxidation bacteria) and NJU-T1(iron-reduction bacteria). Atomic force microscopy (AFM) was utilized to study the morphology and surface roughness of each species. Effects of EPS components on pyrite dissolution were investigated to interpret the relations between EPS and roughness of bacteria surface as well as bioleaching of pyrite. The preliminary data indicate that NJU-AMDS2and Acidithiobacillus ferrooxdians are quite different in surface roughness. A.f in different growth phase exhibit different surface characterization as well, which might be a result of EPS with different amount and different components.Four parallel experiments were carried out to study pyrite bioleaching affected by the mixture of iron-reduction bacteria (NJU-AMDS2) and iron-oxidation bacteria (NJU-T1). The influences of acidity and initial concentration of ferric iron during the process of pyrite bioleaching were investigated as well. The preliminary data indicate that the iron-reduction strain (NJU-T1) plays a vital role in the Fe cycling, especially with the coexistence of iron oxidation strain (NJU-AMDS2). NJU-AMDS2can live on the oxidation of soluble ferrous iron and facilitate consequent precipitation of ferric iron. NJU-AMDS2can also survive through the oxidation of pyrite when there is not enough ferrous iron, causing precipitation with a high ratio of S/Fe. The acidity of solutions can affect the growth and functioning of NJU-AMDS2and NJU-T1a lot. Almost no changes occurred to the acidity throughout the21-day experiment when the pH was low. However, the two bacterial strains did play important role at a higher pH.