Geomicrobiological investigation of two different mine waste tailings generating acid mine drainage

Abstract:

The impact of microbiological metal sulfide oxidation on acid mine drainage generation was studied for two different mine tailings. Microorganisms were quantified using different methods: (1) SYBR Green II direct counting, (2) TaqMan quantitative, real-time PCR (Q-PCR), (3) catalyzed reporter deposition–fluorescence in situ hybridization (CARD-FISH) and (4) most probable number (MPN) cultivation of acidophilic Fe(II) oxidizers. Potential pyrite or pyrrhotite oxidation rates were measured by microcalorimetry.

In the uncovered, pyrrhotite-containing tailings near Selebi-Phikwe, Botswana, acidophilic Fe(II)-oxidizing microorganisms were present in high numbers (MPN) of up to 107 cells g− 1 dw (mean value 3 × 106 cells g− 1 dw) throughout the entire water unsaturated, oxidized zone of about 25 m (at the tailings dam periphery) with a paste pH in the range of 3–4. Mean numbers of living Bacteria (CARD-FISH) and total microorganisms (SYBR Green II) were 1 × 107 cells g− 1 dw and 8 × 107 cells g− 1 dw, respectively. Cell numbers obtained by Q-PCR analysis were in the same range. The average potential pyrrhotite oxidation rate measured by microcalorimetry was 3.4 × 10−4 mol pyrrhotite m− 3 tailings s− 1 at 25 °C. About half of the pyrrhotite oxidation activity was biologically catalyzed.

By contrast, in the covered pyrite-containing tailings in Impoundment 1 in Kristineberg, northern Sweden, acidophilic Fe(II)-oxidizing microorganisms (mean value 5 × 10cells g− 1 dw) were only detected in a distinct zone of oxidized tailings between the cover and the unoxidized tailings where low pH values down to 3 prevailed. Bacterial numbers obtained by Q-PCR analysis were much higher (mean value 3 × 108 cells g− 1 dw). The proportion of biological pyrite oxidation was up to 100% for the oxidized zone. The average potential pyrite oxidation rate was 1.6 × 10−5 mol pyrite m− 3 tailings s− 1 at 10 °C, an order of magnitude lower than that for the pyrrhotite-containing tailings.

 


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