Abstract
Reactive pyritic mine tailings can be populated by chemolithotrophic prokaryotes that enhance the solubilities of many metals, though iron-reducing heterotrophic microorganisms can inhibit the environmental risk posed by tailings by promoting processes that are the reverse of those carried out by pyrite-oxidising autotrophic bacteria. A strain (IT2) of Curtobacterium ammoniigenes, a bacterium not previously identified as being associated with acidic mine wastes, was isolated from pyritic mine tailings and partially characterized. Strain IT2 was able to reduce ferric iron under anaerobic conditions, but was not found to catalyse the oxidation of ferrous iron or elemental (zero-valent) sulfur, and was an obligate heterotrophic. It metabolized monosaccharides and required small amounts of yeast extract for growth. Isolate IT2 is a mesophilic bacterium, with a temperature growth optimum of 30 °C and is moderately acidophilic, growing optimally at pH 4.0 and between pH 2.7 and 5.0. The isolate tolerated elevated concentrations of many transition metals, and was able to grow in the cell-free spent medium of the acidophilic autotroph Acidithiobacillus ferrooxidans, supporting the hypothesis that it can proliferate in acidic mine tailings. Its potential role in mitigating the production of acidic, metal-rich drainage waters from mine wastes is discussed.
Highlights
Waste materials from metal mining, such as mineral tailings, have little or no economic value, making their exploitation not profitable
Homogenized tailing samples were serially diluted onto solid medium that contained 5 mM fructose/0.02% (w/v) yeast extract, acidophile basal salts (ABS) and trace elements (TE) [15], adjusted to pH 3.5 with sulfuric acid, and incubated aerobically for 14 days at 30 ◦C
The isolate was able to use a relatively limited range of defined organic substrates, including glucose, fructose and galactose, compared with Acidobacterium capsulatum and Acidiphilium cryptum found in mine tailings
Summary
Waste materials from metal mining, such as mineral tailings, have little or no economic value, making their exploitation not profitable. Mine tailings are one of the major waste products generated during the mining of metal ores, and have variable physical and chemical compositions, dependent on the ore body being processed and the mining operations [1]. The fine-grain mineral wastes produced (tailings) may account for up to 99% of the primary ore body [2]. While the mineralogical composition of tailings is highly variable, they frequently contain significant amounts of potentially acid-generating minerals, such as pyrite (FeS2), though the acidity generated in fresh tailings can be neutralized by basic materials, such as lime (CaO), that are often added to enhance froth flotation [3]
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