Biomining is a term applied to designate the technical extraction of metals from ores, mineral concentrates and waste materials by microbial activity. Some bacteria are able to release metals from minerals through their action. Bacteria, like any other organism or “life form”, need sources of energy to grow and develop themselves. If you think about us, human beings need to eat and drink water to survive. That is the same with these tiny organisms. However, their energy source is a bit different from ours.
My name is Tamara, the SULTAN ESR number 8, and I am a microbiologist from Brazil. Currently, I am working at the Clausthal University of Technology in Clausthal-Zellerfeld, Germany. As part of the SULTAN team, my project involves the extraction of value metals (Cu, Zn and Pb) that remain in three mining tailings ponds in Europe through (Bio)-Hydrometallurgy processes.
You may be wondering, “What does microbiology have to do with metal extraction or mine wastes? How do they match?” No need to get confused, dear readers. I had these same questions in my mind when I started working at a Research Center in Brazil. However, there I found out a new field of knowledge in the Biotechnology area: the BIOMINING. Have you ever heard about this technology before? Not yet? Do not worry! I can explain to you what that means in my blog text. Perhaps, you will discover that microorganisms, such as the bacteria, do not only cause diseases and force you to take antibiotics, but they can also participate and contribute to innumerable processes in our planet. Curious? So, come with me!
A good thinking point: Before start talking about this amazing technology, if you have any questions about what a mineral is and why it is important to all of us, I would strongly recommend that you read the blogs of my colleagues Alexandra (ESR1) and Srećko (ESR2).
Getting to the heart of the matter
Biomining[1] is a term applied to designate the technical extraction of metals from ores, mineral concentrates and waste materials by microbial activity.
Yes! That is exactly what you just read. Some bacteria are able to release metals from minerals through their action. But, how do they do it? Let me try to explain.
Bacteria, like any other organism or “life form”, need sources of energy to grow and develop themselves. If you think about us, human beings need to eat and drink water to survive. That is the same with these tiny organisms. However, their energy source is a bit different from ours.
Some microorganisms are able to survive under extreme conditions, such as acids sites and under low or high temperature. Can you imagine any kind of life living on the Antarctic ice? Or, near a volcano where the temperature can reach 100°C? Spoiler alert – Some species of bacteria can be found there! Amazing, no!?
Bacteria can also be found in acid mine environments, especially in mines that extract sulfide minerals, that is, minerals containing sulfur (S) combined with a metal in their structure[2].
![Figure 1. Examples of “natural biomines” [3]: (a) the abandoned opencast operation and (b) the Afon Goch draining the former Mynydd Parys mine in north-west Wales; (c) the Rio Tintillo in south-west Spain, the catchment of waters percolating through a vast area of abandoned mine waste (shown in the back of the image).](https://i0.wp.com/news.sim2.be/assets/kcfinder/upload/images/natural-biomines.png?w=620&ssl=1)
Figure 1. Examples of “natural biomines” [3]: (a) the abandoned opencast operation and (b) the Afon Goch draining the former Mynydd Parys mine in north-west Wales; (c) the Rio Tintillo in south-west Spain, the catchment of waters percolating through a vast area of abandoned mine waste (shown in the back of the image).
The presence of some chemical elements such as sulfur (S) and iron (Fe) in those places are excellent energy sources for some species of bacteria, called acidophilic bacteria. They transform the Fe2 into Fe3 , through a process called oxidation, and also produce a strong acid from the sulfur element, the sulfuric acid or H2SO4. Both processes catalyzed by the acidophilic bacteria are responsible for improving the extraction of metals from these sulfide minerals.
Unfortunately, I am going to talk a little about chemistry now. However, there is no need to get desperate! I swear this is not so complicated.
Three major chemical reactions occur in the presence of a sulfide mineral, oxygen and water[1, 4]:
MS 2Fe3 -> M2 2Fe2 S0 (eq. 1 –natural occurrence)
2Fe2 0.5O2 2H -> 2Fe3 H2O (eq. 2 – catalyzed by the bacteria)
S0 1.5O2 H2O -> 2H SO4-2 (eq. 3 – catalyzed by the bacteria)
The letter M written in equation 1 means Metal and, as I explained before, Metal (M) Sulfur (S) = sulfide mineral or MS as depicted. Generally, a MS also contains iron (Fe) in its composition or, if not, they are finding associated with those containing this element. This reaction (eq. 1) may occur naturally in the environment where, for example, the oxygen (O2) from the air and the water (H2O) from rain are present. Consequently, there are release of the metal (M 2) and the sulfur (S0), with reduction of Fe3 to Fe2 . Reactions 2 and 3 can also be carried out naturally, however, this takes a long time to happen.
Bacteria use Fe2 and S0 as energy source. Fe2 is oxidized to Fe3 (eq. 2), regenerating this element to the environment and increasing the speed of the reaction. On the other hand, S0 is transformed into sulfuric acid (H2SO4) (eq. 3). This acid will attack the mineral structure facilitating the release of the metal (M 2) and, consequently accelerating the overall process. The figure below summarizes this route (Figure 2).
Figure 2: Scheme of Biomining: Bioleaching and Biooxidation reactions. Adapted from [4].
Note: The release of the metal is technically called leaching. Bioleaching and Biooxidation are the names of the processes that take place in a Biomining system and both methods occur together.
Indeed, these processes can also be developed chemically with the addition of synthetic acids and oxidizing agents, and that has already happened industrially. Nevertheless, Biomining is so much environment-friendly and interesting, do not you agree with me?!
Thanks for reading! I look forward to seeing you again!
Literature research:
[1] Johnson, D Barrie 2014. Biomining — biotechnologies for extracting and recovering metals from ores and waste materials. DOI: http://dx.doi.org/10.1016/j.copbio.2014.04.008
[2] Vaughan, D J & Corkhill C L 2017. Mineralogy of Sulfides. DOI: https://doi.org/10.2113/gselements.13.2.81.
[3] Johnson, D Barrie 2018. The Evolution, Current Status, and Future Prospects of Using Biotechnologies in the Mineral Extraction and Metal Recovery Sectors. DOI: https://doi.org/10.3390/min8080343
[4] Guezennec, A G. La biolixiviation: apport des biotechnologies pour la valorisation des minerais et des déchets. https://www.e4m.fsg.ulaval.ca/fileadmin/documents/Evenements/PPT_Guezennec.pdf