Inhibiting Effect of Natural Organic Acids on Microbially Mediated Dissolution of Pyrite in Acidic Environments.

Abstract

Natural organic acids, such as tannic acids (TA), wood vinegar (WV), fulvic acids (FA), and humic acids (HA), were investigated as suppressants of microbially mediated dissolution of pyrite with Thiobacillus ferrooxidans and Thiobacillus thiooxidans in acidic media at pH 2∼4, and the suppression mechanism is discussed. The suppression occurs by adsorption of natural organic acids on pyrite, inhibition of cell growth, as well as reduction and complexation of Fe(？) ions. Most of these factors are affected by pH：the suppression by FA was stronger at pH 2 than at pH 3∼4, because the affinity between pyrite and the aromatic groups in FA is stronger below the isoelectric point (iep) of pyrite (around pH 2.5). Cell growth was more strongly inhibited by natural organic acids at lower pH. The order of suppression was WV > TA >> FA > HA at all pHs here, and dependent on the number of functional groups, such as phenolic and carboxylic groups in the natural organic acids. The pKa of WV was ∼5.0, and the acid-base titration and elemental analysis suggested that WV contains acetic acid and large amounts of other organic acids. Wood vinegar was found to suppress and retard pyrite dissolution over a wide pH.