Suppression of microbially mediated dissolution of pyrite by originally isolated fulvic acids and related compounds

Originally isolated fulvic acids (FA) were applied to the suppression of microbially mediated dissolution of pyrite by Thiobacillus ferrooxidans and Thiobacillus thiooxidans, and compared with tannic acids (TA) and oxalic acid (OA). The mechanism of suppression was studied using X-ray photoelectron spectrometry, Fourier transformed infrared spectroscopy, and solution analysis. Preliminary experiments showed that the reaction rate of Fe(III) with pyrite was faster than the rate of reduction of Fe(III) to Fe(II) by FA, and that FA adsorbed to the pyrite surface and moderately suppressed dissolution of the pyrite. Release of S and Fe species and decreases in pH in the microbially mediated dissolution of pyrite were effectively suppressed in the presence of more than 10 ppm of TA, 200 ppm of FA, and 250 ppm of OA. The suppression was considered to be due to the inhibition of microorganisms by organic acids and their adsorption to the active sites of pyrite surfaces in addition to reduction and complexation of Fe(III) ions by these acids. The results indicate that humic substances are useful for remediation in mine environments.