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

Pyrite oxidation occurring in solutions containing iron oxidizing autotrophic bacteria, Acidithiobacillus ferrooxidans (A. ferrooxidans), and/or heterotrophic bacteria, Acidiphilium acidophilum (A. acidophilum), has been investigated. Under the conditions used, the amount of pyrite oxidized in the presence of both species was similar to the amount oxidized in the presence of A. ferrooxidans alone over a period of 30 days. Pretreatment of pyrite with the phospholipid, [1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (23:2 Diyne PC)], to form an adsorbed organic layer reduced the amount of pyrite oxidation in the absence of bacteria and in the presence of A. ferrooxidans. The addition of lipid to pyrite prior to its exposure to a mixed A. ferrooxidans/A. acidophilum solution also showed initial oxidation suppression. However, after 4–5 days the effectiveness of the lipid in suppressing pyrite oxidation was lost and oxidation of the mineral proceeded at a rate that was similar to lipid-free pyrite in the presence of both microbial populations. If, however, lipid/pyrite was pretreated with UV radiation to induce cross-linking of the lipid tails (via polymerization of diacetylene groups in the tails), the lipid layer showed a strong suppression of pyrite oxidation for up to at least 30 days in the presence of both microbial populations. It was also shown with in situ atomic force microscopy (AFM) that the introduction of lipid to pyrite with colonized A. ferrooxidans led to the displacement of a fraction of surface bound bacteria. This lipid-induced displacement was confirmed by ex situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR).