Microbial sulfate reduction in the oxic sediments of sulfide ore mine tailings
Project Coordinator: Olga Karnachuk
Mining of metallic ore deposits produce large volumes of various wastes containing metal sulfides. When the sulfides are exposed to oxygenated water, they oxidized and produced acid water laden with sulfate, metal and metalloids. The weathering of Fe-containing minerals, like pyrite, marcasite (FeS2), pyrrhotite (Fe1-xS) and mackinawite ((Fe,Ni)9S8), causes the largest environmental problem facing the industry today, so-called acid mine drainage (AMD) or also referred as acid rock drainage (ARD).
Microbial processes play major role in sulfide mineral oxidation, as well as, they do in a counteracting process of secondary sulfides precipitation. Dissimilatory sulfate reduction is the most important mechanism of metal sulfide formation and alkalinity generation in mining sites impacted by acid drainage waters.
Sulfate-reducing prokaryotes (SRP) use organic compounds (CH2O) or hydrogen as electron donor and sulfate as electron acceptor to gain energy.
The end product of sulfate reduction, hydrogen sulfide, reacts with metal ions pecipitating them as metal sulfides with very low solubility constant.
These basic reactions underline numerous on-site and off-site techniques aimed to mitigate metal pollution in waste water and mine drainage.
2CH2O + SO42- + 2H+ --> 2CO2 + H2S + 2H2O
Me2+ + H2S --> MeS + 2H+
(Me2+ = Fe2+; Cu2+; Ni2+; Co2+; Cd2+; Zn2+; Pb2+)
Microbial sulfate reduction (MRS) has traditionally been regarded as an anaerobic process and most earlier studies of sulfate-reducing bacteria activity and diversity focused on the reduced subsurface zone of mine tailings.
Our understanding of microbial sulfate reduction has been substantially changed over the last couple of decades. We learnt that many of SRP could tolerate oxygen and grow under nearly atmospheric oxygen level and not only reduce sulfate but use oxygen as a terminal electron acceptor
The aim of this project to assess the activity and diversity of SRP in the oxidized surface layer of a gold mine tailings heavily polluted with metals.
Gold mining in Novyi Berikul’ (Kuzbass Basin) was carried out in 1933-1941 and 1949-1951. The facilities for milling, flotation, and cyanidation of the ore concentrate was at the shore of the Mokryi Berikul' river. The wastes were collected at the same site, in the tailings area separated by a tailings dam. Some of the tailings sediments were removed in late 1990s and covered with barren rock. The remaining sediments still undergo oxidation, resulting in numerous seepages with low pH and high concentration of dissolved metals.
The sulfate-reduction rate measured with 35SO4-tracer reached up to 60 nm/cm3/day.
Molecular cloning only revealed spore-forming Firmicutes, capable of dissimilatory sulfate reduction, to be present in the tailings. No Deltaproteobacteria were found by cloning, denaturation gradient gel electrophoresis of 16S rRNA genes (PCR-DGGE), or cultivation.
Molecular cloning of the dsrAB gene, a functional gene marker of sulfate reduction, three distinct groups of clones. Two of them have no close cultivated relatives. The third group branches among Gram-positive Desulfosporosinus.
Neighbor-joining phylogenetic tree based on 16S rRNA gene sequences of reference cultures from databases and DGGE fragments (511-560 bp) between E. coli position 358 and 956. Sequence names in bold represent sequences retrieved from excised DGGE bands
Karnachuk, O.V., Gerasimchuk, A.L., Banks, D., Frengstad, B., Stykon, G.A., Tikhonova, Z.L., Kaksonen, A.H., Puhakka, J.A., Yanenko, A.S., and Pimenov, N.V. (2009) Bacteria of the sulfur cycle in the sediments of gold mine tailings, Kuznetsk Basin, Russia. Microbiology 78 (4), 483-491.
Karnachuk, O.V., Pimenov, N. V., Yusupov, S. K., Frank, Y. A, Kaksonen, A. H., Puhakka, J. A., Ivanov, M.V., Lindström, E. B., and Tuovinen, O. H. 2005. Sulfate reduction potential in sediments in the Norilsk Mining area, Northern Siberia. Geomicrobiol. J. 22, 11-25.
Kaksonen, A. H., Dopson, M., Karnachuk, O., Tuovinen, O. H., and Puhakka, J. A. 2008. Biological iron oxidation and sulfate reduction in the treatment of acid mine drainage at low temperatures. In: Psychrophiles: from Biodiversity to Biotechnology, Eds. R. Margesin et al., pp. 429-454, Springer Verlag, Berlin.