Deferrization of Kaolinic Sand by Iron Oxidizing and Iron Reducing Bacteria

Abstract

Iron oxidizing bacteria Acidithiobacillus ferrooxidans, iron reducing bacteria Acidiphilium spp. and their mixture were applied for leaching of iron impurities from quartz sand. The bacterial leaching was carried out in order to decrease the amount of colouring iron oxides and to improve the technological properties of the raw material. Mineralogical analysis confirmed the presence of siderite, iron-bearing muscovite and various amorphous and crystalline forms of iron oxides occurring both free and coating siderite and quartz particles. Mössbauer spectroscopy revealed various oxidation and magnetic states of iron ions, with the prevalence of reduced ionic species. Highest extraction of iron was achieved with pure culture of iron-reducing bacteria with ferrous iron as dominant species in the leaching liquor. Surprisingly, iron oxidizing bacteria caused passivation of the surface of iron-bearing minerals, resulting in the depression of iron leaching in comparison with abiotic control. Ferric iron was major species in the leaching solution containing the mixed culture of iron-oxidizing and iron-reducing bacteria. The mixture was far less efficient in iron extraction than pure culture of iron-reducing bacteria.