The role of bacteria in the formation of acid from certain sulfuritic constituents associated with bituminous coal. II. Ferrous iron oxidizing bacteria.

Many bituminous coal mine effluents contain, along with other ions, high concentrations of ferrous iron. This is brought into solution by sulfuric acid produced by the oxidation of sulfuritic material, possibly iron sulfides in part, occurring with bituminous coal (Leathen et al., 1952). The ferrous iron is oxidized by bacteria to the ferric state at a more rapid rate than can be accounted for by a strictly chemical reaction. Colmer and Hinkle (1947) observed an unidentified bacterium rapidly oxidized the ferrous iron of sterilized mine water to ferric iron. Leathen and Madison (1949) found that the ferrous iron of acid mine water containing 350 ppm ferrous iron was completely oxidized by bacteria in five to eight days. Only 48 per cent of the ferrous iron of bacteria-free solutions that contained the same amount of ferrous iron was oxidized in two years. Pure cultures of bacteria, capable of rapidly oxidizing ferrous iron, were isolated by the use of a synthetic inorganic medium closely resembling acid mine water (Leathen et al., 1951). "Sulfur ball" material containing FeS2 is the most common sulfuritic constituent of bituminous coal seams and related rock strata. This undergoes slow chemical oxidation. Leathen and Braley (1950, 1951) reported that pure cultures of the iron oxidizing bacteria effected a several-fold increase in the amounts of acid and sulfate formed from the "sulfur balls". It was found (Leathen and Braley, 1952) that pure cultures of the iron oxidizing bacteria dissociated from the mucoid to the smooth phase, with the latter phase losing the ability to oxidize ferrous iron rapidly. Recently, iron oxidizing bacteria have been isolated by Beck (Personal Communication) from Bingham Canyon, Utah. The isolation of iron oxidizing bacteria by the use of a "natural" mine water medium was reported by Colmer, Temple, and Hinkle (1950). Many properties of the microorganism such as the oxidation of thiosulfate to sulfuric acid closely resembled those of the genus