Bioleaching of pyrite by defined mixed cultures of moderately thermophilic acidophiles

摘要

Leaching of pyrite concentrate and ground rock pyrite was investigated using defined pure cultures and consortia of moderately thermophilic bacteria. Four species of acidophiles were used: (ⅰ) a thermotolerant Leptospirillum isolate (strain MT6); (?) Acidithiobacillus caldus (strain KU); (ⅲ) a novel Gram-positive bacterium 'Caldibacillus ferrivorus' (strain GSM); (ⅳ) a Sulfobacillus isolate. Parameters measured included total iron solubilized, ferrous and ferric iron concentrations, dissolved organic carbon (DOC), pH, Eh and numbers of different bacterial species. Pure cultures of both Leptospirillum MT6 and At. caldus did not accelerate the oxidative dissolution of pyrite concentrate, while both 'C. ferrivorus' and the Sulfobacillus sp. were able to do so, albeit at relatively slow rates and at low redox potentials. The most effective dissolution of pyrite was observed in mixed cultures that included Leptospirillum MT6, all of which maintained relatively high redox potentials (ca. +900 mV). The pH of mixed cultures which contained At. caldus were consistently lower than other cultures, presumably as a result of enhanced oxidation of reduced sulfur compounds formed during the oxidative attack on pyrite by biogenic ferric iron. Numbers of planktonic-phase At. caldus also exceeded those of all other acidophiles in mixed cultures, generally by an order of magnitude or more, while Leptospirillum MT6 was the dominant iron-oxidizing acidophile. The data indicated that the thermotolerant Leptospirillum isolate was the most significant acidophile in the consortia and that At. caldus, although active in generating acidity and numerically the dominant acidophile present in mixed cultures, contributed nothing either directly or indirectly to pyrite oxidation.