The isolation and use of iron-oxidizing, moderately thermophilic acidophiles from the Collie coal mine for the generation of ferric iron leaching solution

Moderately thermophilic, iron-oxidizing acidophiles were enriched from coal collected from an open-cut mine in Collie, Western Australia. Iron-oxidizers were enriched in fluidized-bed reactors (FBR) at 60°C and 70°C; and iron-oxidation rates were determined. Ferrous iron oxidation by the microbiota in the original coal material was inhibited above 63°C. In addition to four iron-oxidizers, closely related to Sulfobacillus spp that had been earlier isolated from the 60°C FBR, one heterotroph closely related to Alicyclobacillus spp was isolated. The Alicyclobacillus sp. isolated from the Collie coal mine tolerated a lower pH than known Alicyclobacillus spp and therefore may represent a new species. The optimum temperature for growth of the iron-oxidizing strains was approximately 50°C and their maximum temperatures were approximately 60°C. The FBR was adjusted to operate at 50°C and was inoculated with all of the isolated iron-oxidizing strains. At 60°C, an iron-oxidation rate of 0.5 g Fe²⁺ 1^-1 h^-1 was obtained. At 50°C, the iron-oxidation rate was only 0.3 g Fe²⁺ 1^-1 h^-1. These rates compare favourably with the iron-oxidation rate of Acidianus brierleyi in shake-flasks, but are considerably lower than mesophilic iron-oxidation rates.