Zammit, and three co-authors, reported in mid-2014 that in situ recovery(ISR) has become an increasingly utilized technology world wide for the economical extraction of uranium (U). Microorganisms play a significant role in U mobilization/immobilization and have therefore been used for the bioremediation of U contaminated sites. In natural environments a wide range of microorganisms have the ability to oxidize or reduce U compounds as part of their metabolism. Hence, microbiota is very likely to play an important role at all stages of U ISR; however the effect of resident microbial communities subject to ISR has not been investigated.
The authors focused on the interactions between microorganisms and U and the possible effects this could have on ISR operations. Microorganisms may affect ISR in either a positive or negative way, e.g., assisting in U mobilization via the oxidation of U or immobilizing U by reducing it into an insoluble form. The use of native microbial communities to influence the mobilization/immobilization of U during ISR could help to increase U recovery rates or speed-up post-mining remediation.
The authors concluded that ISR is a mature technology for U mining, and may serve as a platform for the development of this method to other commodities as well. Not only does the potential for using microorganisms in ISR exist, microorganisms undoubtedly play a yet-undetermined role in current U ISR operations. In the case of sandstone-hosted deposits, the ISR process essentially involves reverse engineering the processes that led to the formation of these deposits. Acidophilic iron, sulfur and U oxidizing microorganisms contributed to the mobilization of U and other metals (Guay et al., 1977), a process common in many environments (Bondici et al., 2013; Kalinowski et al., 2004; Mohagheghi et al.,1985; Merroun and Selenska-Pobell, 2008; North et al., 2004). A detailed understanding of microbial community structures and their functions will lead not only to improved understanding of ore formation processes and controls on ore grade and mineralogy, but also has direct implications for the optimization of the ISR process. In terms of microorganism communities, ISR provides new opportunities and challenges, which will increase the rate and diversity of microbial activity, as has been observed in the case of U-contaminated aquifers (Castelle et al.,2013; Gihring et al., 2011; Wu et al., 2006a, 2006b).
Microorganisms can interact with U mobility in via a wide variety of pathways (e.g., direct oxidation and reduction of U; controlling oxido-reduction of species that interact with U(e.g., Fe2+/Fe3+);controlling release and speciation of solubility-controlling ligands such as PO42−), either assisting or hindering U extraction. Encouraging or retarding the growth of these microorganisms could improve U extraction rates. The opportunity exists here for researchers to frontier the development of microbially assisted ISR operations as well as further developing bioremediation strategies.
[Also see Rackley, R. I., (here)]
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