(164c) Thermoacidophilic Archaea Enhance Bioleaching of Chalcopyrite for Copper Recovery

As the availability of critical metals (e.g., copper, nickel, uranium) declines, there is a need for recovery processes that are efficient and environmentally friendly. Bioleaching is one option and now accounts for over 15% of the copper recovered worldwide, but processes are rudimentary and slow. Pilot-scale data show that extremely thermoacidophilic microorganisms from the domain Archaea can leach copper at much higher rates and yields than mesophilic bacteria, although the reasons for this enhancement are not known[1]. Among these thermoacidophiles, members of the order Sulfolobales have attracted the most attention. Key to the effectiveness of these archaea is the function of the fox cluster, which encodes proteins that catalyze iron oxidation[2], their ability to use reduced inorganic sulfur compounds as an energy source[3], the formation of biofilms on mineral surfaces[4], and the regulation of biotic and abiotic reactions to release copper from ores[5].

Chalcopyrite (CuFeS₂) is the most abundant source of copper. Copper extraction in chalcopyrite involves the oxidation of the mineral initially, releasing copper, sulfur, and ferric iron. If ferric iron is oxidized to ferrous iron, it can also lead to chalcopyrite oxidation, leading to more copper release from the ores. However, this process is slow. In addition, formation of sulfur or sulfur compounds on the surface of the mineral might lead to passivation, limiting access to the surface of the mineral and thus, hindering the leaching process. The characteristics of thermoacidophiles enhance bioleaching, since several members are known to oxidize iron or sulfur. Furthermore, the acidic environment, and the high temperature in which these microorganisms grow, have shown to further increase the leaching rates. Among these thermoacidophiles is Sulfolobus acidocaldarius (Saci), not known to be a good sulfur oxidizer, but has available genetic tools for metabolic engineering via an uracil-auxotrophy. Efforts are underway to engineer this archaeon to be a bioleacher[6].

Here, thermoacidophiles from the order Sulfolobales were examined for their potential for iron and chalcopyrite oxidation. Furthermore, the bioleaching process is optimized using the galvanic interactions between pyrite and chalcopyrite in a reaction containing the mixture. Biofilm formation of the microorganisms are investigated on the surface of the mineral. Finally, metabolic engineering tools of Saci are being used to modify its metabolism to enable it to bioleach chalcopyrite via enhanced iron and sulfur oxidation.

References

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[2] J. A. Counts, N. P. Vitko, and R. M. Kelly, “Fox Cluster Determinants for Iron Biooxidation in the Extremely Thermoacidophilic Sulfolobaceae,” Environ. Microbiol..

[3] K. S. Auernik and R. M. Kelly, “Identification of components of electron transport chains in the extremely thermoacidophilic crenarchaeon Metallosphaera sedula through iron and sulfur compound oxidation transcriptomes,” Appl. Environ. Microbiol., vol. 74, no. 24, pp. 7723–7732, 2008.

[4] A. M. Lewis et al., “The biology of thermoacidophilic archaea from the order Sulfolobales,” FEMS Microbiol. Rev., no. fuaa063, Jan. 2021, doi: 10.1093/femsre/fuaa063.

[5] K. S. Auernik and R. M. Kelly, “Impact of Molecular Hydrogen on Chalcopyrite Bioleaching by the Extremely Thermoacidophilic Archaeon <em>Metallosphaera sedula</em>,” Appl. Environ. Microbiol., vol. 76, no. 8, p. 2668, Apr. 2010, doi: 10.1128/AEM.02016-09.

[6] B. M. Zeldes et al., “Determinants of sulphur chemolithoautotrophy in the extremely thermoacidophilic Sulfolobales,” Environ. Microbiol., vol. 21, no. 10, pp. 3696–3710, 2019.