A Study on the Interaction Mechanisms between Uraninite and Microbe Leaching Solutions

Uranium (U) bioleaching represents a promising technology for U recovery; yet, the mechanisms of interaction between microorganisms and U minerals remain poorly constrained. In particular, whether microorganisms directly oxidize U minerals has yet to be fully elucidated. In this study, uraninite—the primary industrially relevant U-bearing mineral—was chosen as the research object, and two bioleaching systems of uraninite (Fe-free and Fe-supplemented) were constructed. In the Fe-free system, adsorbed bacteria cells adhered tightly to the uraninite surface via extracellular polymeric substances (EPS). During interaction with the bioleaching solution, uraninite exhibited the formation of corrosion pits, and the U leaching rate was markedly higher than that in the sulfuric acid system, supporting the operation of a direct microbial mechanism during U bioleaching. However, relying solely on this direct mechanism is insufficient to enhance leaching efficiency substantially in the Fe-free system. Limited energy substrates and the relatively high U concentration in the leachate triggered bacterial self-detoxification, promoting the formation of uniform rose-like uramphite ((NH4)(UO2)(PO4)•3H2O) crystals to mitigate uranium and heavy metal toxicity, as well as the accumulation of electron-dense particles mainly composed of Cu, Pb, and Fe. In the Fe-supplemented system, the indirect mechanism contributed approximately 72.22% to U extraction, whereas the direct mechanism accounted for only 20.97%. After 15 h, the aqueous conditions favored jarosite (KFe3(SO4)2(OH)6) formation, prompting massive amounts of Fe(III), K+, and SO42- to precipitate. Associated acid generation decreased pH sharply before stabilization, highlighting that precise pH control, favoring microbial growth while inhibiting jarosite formation, is key to optimizing U bioleaching efficiency. The findings provide a theoretical basis for the artificial regulation of microbial U-leaching processes and have significant implications for advancing technological development efficiently to develop U resources.
Keywords: U bioleaching, biohydrogeochemistry, mineral-solution interface reaction, direct mechanism, indirect mechanism.