Microenvironments determining growth of acidophilic bacteria in Zn-Pb flotation tailings of neutral reaction

Zinc and lead ore flotation tailings deposited in the Olkusz region show a neutral reaction. They are composed of dolomite-type minerals (alkaline), mostly Ca, Mg(C0₃)₂ and Ca, Mg, Fe(COj)₂ (70%), and other minerals including sulphides (acid), mainly pyrite and marcasite (FeS ₂; up to 20%). Sulphur and iron concentration in tailings reaches the levels of 7-14% and of 8-16%, respectively. The microenvironments rich in sulphide minerals present in waste materials which indicate almost neutral reaction allow the metabolic activity of acidophilic sulphur-and iron-oxidizing bacteria of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans species to be grown and developed, in spite of the alkaline character of basic mineral components in the tailings examined.