Insights on uranium removal by ion exchange columns: The deactivation mechanisms, and an overlooked biological pathway

Ion exchange (IX) is an attractive approach to extract uranium from wastewater, simultaneously reducing the negative environmental impact of uranium mining and recovering uranium resources. However, the IX process is limited by the deactivation of the resin, and the role played by microorganisms attached to the resin remains unknown. Here, we characterized the chemical and mineralogical compositions, microbial community structure, and network-related molecular mechanism of the uranium-bearing deposit on SBA exchange resin from a fullscale U mine seepage water treatment system. The uranium removal by the resin was attributed to the formation of binary anionic UO2(SO4)(2)(2-) or UO2(SO4)(3)(4-) complexes and their subsequent association with the resin. The deactivation of the resins might mainly result from the presence of deposits on the resin surface rather than the saturation of functional groups. Microbial reduction of U(VI) to U(IV) was confirmed in the deposit. The long-term operation acclimated functional microbial communities on the resin, such as Curvibacter sp., Acidovorax sp., and Herminiimonas sp. for uranium bioremediation, Methylotenera sp. for biofilm formation, and Polaromonas sp. and Hydrogenophaga sp. for autotrophic metabolism. Molecular ecological network analysis indicated the synthetic metabolisms among metal remediation bacteria and autotrophs might play major roles in microbial-mediated uranium removal. This study offers new insights into the application of the IX system for uranium-containing wastewater treatment.