Acidophilic iron-oxidizing bacteria

Among the acidophilic iron-oxidizing bacteria, Acidithiobacillus ferrooxidans (Kuenen, 1989) and Leptospirillum ferrooxidans (Eccleston et al., 1985) are well... 

In the corroded concrete, there also reside acidophilic iron-oxidizing bacteria (see below) besides the usual sulfur-oxidizing bacteria. The acidophilic iron-oxidizing bacteria show optimal growth pH at 2.0, and oxidize not only ferrous iron but also sulfur compounds. Therefore, they can participate in the corrosion of concrete. We have to consider the action of both the usual sulfur-oxidizing bacteria and the acidophilic iron-oxidizing bacteria when we exploit the compounds which inhibit the bacterial corrosion of concrete. 

Are there any methods to inhibit the growth of the bacteria participating in the corrosion of concrete A few compounds have been exploited which inhibit the growth of the sulfur-oxidizing and acidophilic iron-oxidizing bacteria. A reagent... 

The author and his colleagues have found that calcium formate completely inhibits the growth of the sulfur-oxidizing bacteria and acidophilic iron-oxidizing bacteria at 50 mM (6500 ppm) or more in laboratory experiments (Yamanaka et al., 2002a). Calcium formate is hardly harmful and as it will finally become calcium carbonate, it is expected that the compound will barely pollute the environment. 

In Nature, there reside bacteria that acquire the energy for life processes by oxidizing ferrous ion to ferric ion. Acidithiobacillus ferrooxidans and Leplospirillum ferrooxidans oxidize ferrous ion to ferric ion at pH 2.0 and are the most well known among the bacteria that oxidize ferrous ion. Ferrous ion is easily oxidized spontaneously by molecular oxygen at neutral pH, while at pH 2.0 it is not oxidized spontaneously but is easily oxidized even at pH 2.0 by the action of the acidophilic iron-oxidizing bacteria. These bacteria are utilized in various industrial processes because of their ability to oxidize ferrous to ferric ions at pH 2.0. In particular, A. ferrooxidans has been well studied industrially as well as scientifically. 

Fig. 5.3. A diagram of the apparatus for the bacterial leaching on a laboratory scale. The acidophilic iron-oxidizing bacteria (e.g., Acidithiobacillus ferrooxidans) are present in the pool and oxidize ferrous ion to ferric ion...

As mentioned above, at present bacterial leaching is not performed in Japan. However, the acidophilic iron-oxidizing bacteria are applied to biohydrometallurgy. 

From the shape (rods) of the bacteria, they appear to be Acidithiobacillus ferro-oxidans but not Leptospirillum ferrooxidans. Finally, when the mixture of the mudstone and the medium for the sulfur-oxidizing bacteria (pH 6.5) supplemented with powdered pyrite is shaken in air, the pH of the culture medium is lowered over time. When the pH is lowered to below 4, the amount of ferrous ion plus ferric ion in the medium increases rapidly together with a parallel increase of sulfate ion (Yamanaka et al., 2002b). These phenomena are not observed with the mudstone heated at 121°C for 20 min. The results show that the acidophilic iron-oxidizing bacteria (growing at pH lower than about 4) oxidize pyrite but the usual sulfur-... 

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