Oxidation of pyrite by Acidianus brierleyi: Importance of close contact between the pyrite and the microorganisms

Abstract

Experiments were done in order to study the thermophilic archaebacterium Acidianus brierkyi during oxidation of pyrite (FeS$. The microorganisms were grown both separated from the pyrite by a membrane and in close contact with the pyrite. From the results it can be concluded that direct contact is needed for good growth of the strain studied. The obtained results indicate that the direct contact mechanism may be applied to oxidation of sulfidic minerals by A. brierleyi. IntroductionThere is a large degree of interest in biohydrometallurgy in order to use bioleaching to recover metals from low-grade ores where conventional methods are not economical. For exampel, gold is often trapped in a matrix of pyrite and arsenopyrite. The pyrite and the arsenopyrite can be dissolved by microorganisms thereby releasing the gold under mild conditions. Copper mining is another example where biohydrometallurgy has become an important process. Microorganisms capable of oxidizing pyrite and other sulfidic minerals have a potential for desulfurization of coal. The major part of the inorganic sulfur in coal consists of pyrite. The mechanism of microbial oxidation of sulfide minerals has been studied for many years. Two types of mechanisms have been proposed for the oxidation of the mineral pyrite (FeS2), a direct mechanism and an indirect mechanism (Eligwe, 1988). In the direct mechanism the microorganisms oxidize the pyrite directly and physical contact between the pyrite and the microorganisms is thought to be essential for the reaction. In the indirect mechanism the pyrite is oxidized chemically by ferric iron and the ferric iron is then regenerated by the microorganisms. The two mechanisms can be described by the following reactions where reactions 1) and 3) are biological.

Analysis of the surface proteins of Acidithiobacillus ferrooxidans strain SP5/1 and the new, pyrite-oxidizing Acidithiobacillus isolate HV2/2, and their possible involvement in pyrite oxidation

“…, which then in turn oxidizes the Fe 2? on the pyrite surface in a strictly abiotic and chemical process (Larsson et al 1993;Fowler et al 1999;Rohwerder et al 2003). The produced Fe 3?…”

Effects of phospholipid on pyrite oxidation in the presence of autotrophic and heterotrophic bacteria

“…Within coal mining regions, oxidation of the mineral, which is facilitated by the presence of microbes, leads to the environmental phenomenon known as acid mine drainage (AMD), that impacts ecosystems primarily through a sulfuric acid laden runoff (Larsson et al, 1993;Nordstrom and Southam, 1997;Edwards et al, 1998;Marchand and Dinkelman, 2006). With an eye toward understanding the chemistry associated with AMD, there has been a significant effort focused on studying the mechanistic details of pyrite oxidation under abiotic and biotic conditions (Shrihari et al, 1991;Solari et al, 1992;Ohmura et al, 1993;Edwards et al, 1999;Elsetinow et al, 2000;Borda et al, 2003;Elsetinow et al, 2003;Hao et al, 2006).…”

Microbial oxidation of pyrite; experiments using microorganisms from an extreme acidic environment

“…The impact of attachment on oxidative dissolution rates is unresolved. In one study using an iron-oxidizing archaea, Larsson et al (1993) showed that close contact between microorganisms and pyrite was necessary for optimum growth and oxidation rates. However, attachment to the sulfide surface did not appear to be necessary.…”