Biogenic radon emission from uranium mine tailings a consequence of microbial leaching.
Two uranium mine waste heaps near Ronneburg, Germany, were investigated for the occurrence of lithotrophic and chemoorganotrophic leach bacteria. The evaluation of 162 samples (= to 5m depth) resulted in the finding that Thiobacillus (T.) ferrooxidans dominated up to a depth of about 1.5m. Below, T. intermedius/neapolitanus were the most abundant lithotrophs. Pyrite, however, was the only nutrient source in the heaps. Consequently, the latter lithotrophs must have had another source of nutrient. We recently demonstrated leaching to proceed only via the indirect mechanism with thiosulfate and ferrous hexahydrate as the first degrdn. products. Thiosulfate is the best nutrient for T. intermedius/neapolitanus. In addn., the highest emission of radon, measured as radioactivity 1m above the heap surface, correlated with the highest cell counts of T. Ferrooxidans. Considering the diagenesis of the ore (pptn. of uranite followed by pyrite) a leach pore model was hypothesized explaining the correlation. Accordingly, the biol. removal of pyrite allows the trapped radon to escape from the pore.
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