Characteristics and adaptability of iron- and sulfur-oxidizing microorganisms used for the recovery of metals from minerals and their concentrates |
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Authors: | Email author" target="_blank">Douglas?E?RawlingsEmail author |
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Institution: | (1) Department of Microbiology, University of Stellenbosch, Private BagX1, 7602 Matieland, South Africa |
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Abstract: | Microorganisms are used in large-scale heap or tank aeration processes for the commercial extraction of a variety of metals
from their ores or concentrates. These include copper, cobalt, gold and, in the past, uranium. The metal solubilization processes
are considered to be largely chemical with the microorganisms providing the chemicals and the space (exopolysaccharide layer)
where the mineral dissolution reactions occur. Temperatures at which these processes are carried out can vary from ambient
to 80°C and the types of organisms present depends to a large extent on the process temperature used. Irrespective of the
operation temperature, biomining microbes have several characteristics in common. One shared characteristic is their ability
to produce the ferric iron and sulfuric acid required to degrade the mineral and facilitate metal recovery. Other characteristics
are their ability to grow autotrophically, their acid-tolerance and their inherent metal resistance or ability to acquire
metal resistance. Although the microorganisms that drive the process have the above properties in common, biomining microbes
usually occur in consortia in which cross-feeding may occur such that a combination of microbes including some with heterotrophic
tendencies may contribute to the efficiency of the process. The remarkable adaptability of these organisms is assisted by
several of the processes being continuous-flow systems that enable the continual selection of microorganisms that are more
efficient at mineral degradation. Adaptability is also assisted by the processes being open and non-sterile thereby permitting
new organisms to enter. This openness allows for the possibility of new genes that improve cell fitness to be selected from
the horizontal gene pool. Characteristics that biomining microorganisms have in common and examples of their remarkable adaptability
are described. |
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