Autotrophic bacteria and the formation of acid in bituminous coal mines.

The passage of water through certain bituminous coal mines results in a solution which is extremely acid in reaction because of its high content of ferrous sulfate, some aluminum sulfate, and lesser amounts of manganese sulfate. The ferrous iron is subsequently rapidly oxidized to the ferric state by an autotrophic bacterium. Autotrophic bacteria have also been implicated in the formation of the ferrous sulfate from iron disulfides in the coal mines. Nevertheless, the extent and exact mechanism of bacterial action in the formation of ferrous sulfate remains obscure. Iron disulfide, which is the original source of the ferrous sulfate, occurs in different forms in the coal and associated strata. These geological and structural aspects of acid formation have been discussed by Temple and Colmer (1951a). Direct bacterial oxidation of iron disulfide has not been demonstrated, although several reports indicate the prevalence of Thiobacillus thiooxidans in soils where pyrite is undergoing oxidation (Drewes, 1928; Jensen, 1927; MacIntire et at., 1930; Quispel et al., 1952; Rudolfs, 1922). Quispel, Harmsen, and Otzen (1952) postulated the initial surface chemical oxidation of ferrous ions, releasing elemental sulfur which could then be oxidized by T. thiooxidans. Early workers at West Virginia University (Carpenter and Herndon, 1933) claimed to have identified T. thiooxidans in acid mine waters and this bacterium was definitely established as a normal inhabitant of acid mine waters by Colmer and Hinkle (1947). These authors also found another bacterium in acid mine drainage which was responsible for the oxidation of ferrous iron to the ferric state in acid solutions where ferrous iron was chemically stable; indeed, this unusual reaction led to the discovery of the bacterium. The ironoxidizing bacterium proved to be an autotroph and has since been described and given the name Thiobacillus ferrooxidanrs n.sp. (Colmer et al., 1950; Temple and Colmer, 1951b). Leathen, Braley, and McIntyre (1953a) stated that T. thiooxidans has no effect upon museum grade pyrite and does not enhance acid formation from "sulfur balls", a type of pyritic concretion commonly found in coal. However, they reported (Leathen et al., 1953b) that the iron-oxidizing bacterium, which we have called 1 Present address: The Texas Co., Bellaire, Texas. Thiobacillus ferrooxidans, does increase the acid formed from "sulfur balls" although not from museum grade pyrite. In their experiments both bacteria produced some acid from museum grade marcasite. The work of Leathen et al. agrees with ours in that T. thiooxidans increases the acid formed from marcasite of non-coal origin, and we have confirmed their observation of the effect of T. ferrooxidans upon "sulfur balls." However, our results show in addition that T. thiooxidans enhances the acid production of certain types of "sulfur balls" and that T. ferrooxidans increases the acid formation from museum grade pyrite. An overall mechanism for the acid formation is proposed.