Microbial communities associated with uranium in-situ recovery mining process are related to acid mine drainage assemblages

Abstract

A large fraction (47%) of the world's uranium is mined by a technique called "In Situ Recovery" (ISR). This mining technique involves the injection of a leaching fluid (acidic or alkaline) into a uranium-bearing aquifer and the pumping of the resulting solution through cation exchange columns for the recovery of dissolved uranium. The present study reports the in-depth alterations brought to autochthonous microbial communities during acidic ISR activities. Water samples were collected from a uranium roll-front deposit that is part of an ISR mine in operation (Tortkuduk, Kazakhstan). Water samples were obtained at a depth of ca 500 m below ground level from several zones of the Uyuk aquifer following the natural redox zonation inherited from the roll front deposit, including the native mineralized orebody and both upstream and downstream adjacent locations. Samples were collected equally from both the entrance and the exit of the uranium concentration plant. Next-generation sequencing data showed that the redox gradient shaped the community structures, within the anaerobic, reduced, and oligotrophic habitats of the native aquifer zones. Acid injection induced drastic changes in the structures of these communities, with a large decrease in both cell numbers and diversity. Communities present in the acidified (pH values < 2) mining areas exhibited similarities to those present in acid mine drainage, with the dominance of Sulfobacillus sp., Leptospirillum sp. and Acidithiobacillus sp., as well as the archaean Ferroplasma sp. Communities located up- and downstream of the mineralized zone under ISR and affected by acidic fluids were blended with additional facultative anaerobic and acidophilic microorganisms. These mixed biomes may be suitable communities for the natural attenuation of ISR mining-affected subsurface through the reduction of metals and sulfate. Assessing the effect of acidification on the microbial community is critical to evaluating the potential for natural attenuation or active bioremediation strategies.

Resident bacterial populations mediating biogeochemical dynamics in a Uranium roll front deposit

“…The next important step in our investigations will be to determine the microbial metabolic activities associated with the distinct aquifer compartments. as was seen in a previous study performed in Kazakhstan ISR mine after acid injection [20]. Although, more acidophilic bacteria and other mixotrophs similar to those abundant in an acid mine drainage, and detected in these pristine waters with low abundance (e.g.…”

“…However, data on water chemistry and bacterial community composition in roll-front context is relatively rare in the literature [20,21].…”

Industrial Deployment of Reactive Transport Simulation: An Application to Uranium In situ Recovery

“…Taking into account the regional hydraulic gradient, mitigation of the residual solutions will occur mainly downstream, where reducing conditions are found. These conditions are confi rmed and explained by the presence of native sulfate-reducing and metal-reducing bacteria involved in the biogeochemical reactions regulating the water composition (Coral et al 2018). (Bio)reduction of sulfate into sulfi de is known to be favorable to the formation of insoluble metallic sulfi de minerals such as pyrite (FeS 2 (s)), therefore participating to the decrease of SO 4 concentration.…”

Pyrite oxidization accelerates bacterial carbon sequestration in copper mine tailings

“…4), indicating high consistency of dominant autotrophic bacterial genera in different mine tailings. It is possible that acidophilic and/or autotrophic bacteria might be stimulated under conditions of pyrite oxidization and the availability of organic carbon (Deng et al, 2016;Antonelli et al, 2018); moreover, the main carbon fixers in these two mine tailings may be derived from the same groups. In addition, levels of major ferrous and sulfur-oxidizing genera, autotrophic Leptospirillum and Acidiphilium in YM_ FeS 2 and autotrophic Thiobacillus in SM_FeS 2 , were enhanced, suggesting the synchronization of pyrite oxidization and carbon sequestration in mine tailings.…”

“…Soil ecosystems have great potential as carbon sinks to stabilize CO 2 and regulate climate change (White et al, 2000). Atmospheric CO 2 can be fixed in plants via photosynthesis and assimilated into soils via decomposition and microbial activity (Deng et al, 2016;Antonelli et al, 2018), and autotrophic bacteria play a significant role in carbon sequestration in soil ecosystems (Berg, 2011;Alfreider et al, 2017). Six autotrophic carbon sequestration mechanisms are widespread, including the Calvin-Benson-Bassham (CBB) cycle, the reductive tricarboxylic acid (rTCA) cycle, the reductive acetyl-CoA pathway, and the recently discovered 3-hydroxypropionate-4-hydroxybutyrate (HP-HB) cycles (Berg, 2011;Alfreider et al, 2017).…”