D. Fortin et al., BIOGEOCHEMICAL PHENOMENA INDUCED BY BACTERIA WITHIN SULFIDIC MINE TAILINGS, Journal of industrial microbiology, 14(2), 1995, pp. 178-185
Mill tailings resulting from mining and metallurgical processes are us
ually disposed of into open-air impoundments, where they become subjec
ted to chemical or microbial leaching. At the surface of the tailings,
where oxic conditions prevail, acidophilic bacteria, such as thiobaci
lli, can oxidize sulfidic minerals (e.g. pyrite and pyrrhotite) and ge
nerate acidic metal-rich leachates as by-products of their metabolism.
This, combined with chemical oxidation, leads to acid mine drainage (
AMD). Biomineralization, whereby a proportion of the metal leachate is
precipitated can also occur in the oxidized tailings, often as a resu
lt of a close metal-bacteria interaction. Iron-rich precipitates are u
sually found on bacterial cell walls, and are thought: to serve as nuc
leation sites for further mineralization within the tailings impoundme
nts. As depth increases in mine tailings, oxygen depletion and the pre
sence of water-saturated pores usually lead to anoxic conditions. Unde
r such redox and chemical conditions, populations of sulfate-reducing
bacteria (SRBs) can colonize the tailings. As a result of their metabo
lic activity, sulfate is reduced to hydrogen sulfide, which in turn ca
n react with dissolved metals to form metal sulfide precipitates. Micr
obial sulfate reduction also generates alkalinity, although chemical d
issolution of carbonate and oxide minerals probably also play an impor
tant role in the generation of alkaline conditions in mine tailings.