Pyrite oxidation in acid sulphate soils
1980
Arkesteyn, G.J.M.W. (Landbouwhogeschool Wageningen (Netherlands). Vakgroep Microbiologie)
A study has been made of microbian processes in the oxidation of pyrite in acid sulphate soil material. Such soils are formed during aeration of marine muds rich in pyrite FeS(,2). Bacteria of the type of Thiobacillus ferrooxidans are mainly responsible for the oxidation of pyrite, causing a pronounced acidification of the soil. However, because Thiobacillus ferrooxidans functions optimally at pH values below 4.0, its activity cannot explain the initial pH drop from approximately neutral to about 4. This was shown to be a non-biological process, in which bacteria play an insignificant part. Although Thiobacillus thioparus and Thiobacillus thiooxidans were isolated from the acidifying soil, they did not stimulate oxidation of FeS(,2), but utilized reduced sulphur compounds, which are formed during the non-biological oxidation of FeS(, S). Ethylene-oxide-sterilized and dry-sterilized soil inoculated with pure cultures or mixtures of various thiobacilli or with freshly sampled acid sulphate soil did not acidify faster than sterile blanks. Thiobacillus thiooxidans, Thiobacillus thioparus, Thiobacillus intermedius and Thiobacillus perometabolis increased from about 10E4 to 10E5 cells/ml in media with FeS(,2) as energy source. However, FeS(,2) oxidation in the inoculated media was not faster than in sterile blanks. Attempts to isolate microorganisms other than Thiobacillus ferrooxidans, like Metallogenium or Leptospirillum ferrooxidans, which might also be involved in the oxidation of FeS(,2) were not successful. Addition of CaCO(,3) to the soil prevented acidification but did not stop non-biological oxidation of FeS(,2)
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