Biostimulation as a sustainable solution for acid neutralization and uranium immobilization post acidic in-situ recovery

Rizlan Bernier-Latmani, Thomas Coral, Pierre Rossi
2022
Article

Résumé

Major uranium (U) deposits worldwide are exploited by acid leaching, known as 'in-situ recovery' (ISR). ISR involves the injection of an acid fluid into ore-bearing aquifers and the pumping of the resulting metal-containing solution through cation exchange columns for the recovery of dissolved U. Rehabilitation of ISR-impacted aquifers could be achieved through natural attenuation, or via biostimulation of autochthonous heterotrophic microorganisms due to the associated acid neutralization and trace metal immobilization. In this study, we analyzed the capacity of pristine aquifer sediments impacted by diluted ISR fluids to buffer pH and immobilize U. The experimental setup consisted of glass columns, filled with sediment from a U ore-bearing aquifer, through which diluted ISR fluids were flowed continuously. The ISR solution was obtained from ISR mining operations at the Muyunkum and Tortkuduk deposits in Kazakhstan. Following this initial phase, columns were biostimulated with a mix of molasses, yeast extract and glycerol to stimulate the growth of autochthonous heterotrophic communities. Experimental results showed that this amendment efficiently promoted the activity of acid-tolerant bacterial guilds, with pH values rising from 4.8 to 6.5 - 7.0 at the outlet of the stimulated columns. The reduction of sulfate, nitrate, and metals as well as dissimilatory nitrate reduction to ammonia induced the rise in pH values, in agreement with geochemical modeling results. Biostimulation efficiently promoted the complete immobilization of U, with the accumulation of up to 3,343 ppm in the first few centimeters of the columns. Synchrotron analysis and SEM-EDS revealed that up to 60% of the injected hexavalent U was immobilized as tetravalent non-crystalline U onto bacterial cell surfaces. 16S rDNA amplicon analysis and qPCR data suggested a predominant role played for members of the Phylum Firmicutes (from the genera Clostridium, Pelosinus and Desulfosporosinus) in biological U reduction and immobilization.

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https://infoscience.epfl.ch/record/291877?ln=fr

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Rizlan Bernier-Latmani, Thomas Coral, Pierre Rossi
2022
Article

Résumé

Official source

https://infoscience.epfl.ch/record/291877?ln=fr

À propos de ce résultat

Concepts associés (15)

Concepts associés

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Publications associées (12)

Publications associées

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Biostimulation as a remediation strategy post uranium acidic in situ recovery

Rizlan Bernier-Latmani, Thomas Coral, Brian Carl Reinsch, Pierre Rossi

A large fraction (47%) of the world’s uranium is mined by a technique called “In Situ Recovery”. This mining technique involves the injection of a leaching fluid (acid or alkaline) into a uranium-bearing aquifer and the pumping of the resulting solution through cation exchange columns for the recovery of the dissolved metal. A strategy of rehabilitation of the aquifer is based on the biostimulation of the autochthonous microbial community to remediate the acid plume and immobilize remaining trace metals. Assessment of the biostimulation was carried out using column tests filled with aquifer material. These columns were stimulated with a mixture of molasses, yeast extract and glycerol. Results showed that this mixture efficiently promoted the development of acid-resistant, sulfate-reducing bacterial guild members down to an inlet pH value ~ 4.7, with pH values at the outlet reaching up to 6.5 – 7. The rise of pH values along the columns were attributed to the predominant reduction of nitrate and sulfate. Biostimulation of the microbial community efficiently promoted the complete immobilization of U in the first centimeters of the columns. Synchrotron x-ray analysis and electron microscopy revealed that up to 60% of total U was precipitated as UIV onto bacterial cells. A detailed metagenomic analysis and qPCR data illustrated drastic changes occurring within the community with the reduction of the microbial diversity and the quantitative development of fermentative bacteria. The community was dominated by members of the Phylum Firmicutes (genus “Clostridium”, Pelosinus and Desulfosporosinus), representing up to 89 % of all cells.

2016

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Biogeochemical controls on the product of microbial U(VI) reduction

Daniel Scott Alessi, Rizlan Bernier-Latmani, Paul Pao-Yun Shao, Malgorzata Alicja Stylo

Biologically mediated immobilization of radio-nuclides in the subsurface is a promising strategy for the remediation of uranium-contaminated sites. During this process, soluble U(VI) is reduced by indigenous microorganisms to sparingly soluble U(TV). The crystalline U(IV) phase uraninite, or UO2, is the preferable end-product of bioremediation due to its relatively high stability and low solubility in comparison to biomass-associated nonuraninite U(IV) species that have been reported in laboratory and under field conditions. The goal of this study was to delineate the geochemical conditions that promote the formation of nonuraninite U(IV) versus uraninite and to decipher the mechanisms of its preferential formation. U(IV) products were prepared under varying geochemical conditions and characterized with X-ray absorption spectroscopy (XAS), scanning transmission X-ray microscopy (STXM), and various wet chemical methods. We report an increasing fraction of nonuraninite U(IV) species with decreasing initial U concentration. Additionally, the presence of several common groundwater solutes (sulfate, silicate, and phosphate) promote the formation of nonuraninite U(IV). Our experiments revealed that the presence of those solutes promotes the formation of bacterial extracellular polymeric substances (EPS) and increases bacterial viability, suggesting that the formation of nonuraninite U(IV) is due to a biological response to solute presence during U(VI) reduction. The results obtained from this laboratory-scale research provide insight into biogeochemical controls on the product(s) of uranium reduction during bioremediation of the subsurface.

Amer Chemical Soc2013

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Knowledge of paleo-redox conditions in the Earth's history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth's crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. Additionally, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.

Natl Acad Sciences2015

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