Ectopic application of zero-valent iron in microbial uranium extraction with concurrent electrical energy generation

Efficient removal and recovery of uranium (U(VI)) from mining wastewater are vital for environmental protection and resource sustainability. Zero-valent iron-assisted microbial U(VI) reduction shows great potential, yet is hindered by inefficient electron utilization, surface passivation, and operational complexity of hybrid systems. This study demonstrated a Fe(0)-based spontaneous microbial electrochemical (Fe(0)-SMEC) system capable of simultaneously removing U(VI) and generating electricity. By spatially separating anodic Fe(0) oxidation from microbial U(VI) reduction at the biocathode, the system significantly enhanced both electron utilization and uranium removal efficiency. Within 48 h, the Fe(0)-SMEC system removed 81.7 %-96.4 % of U(VI) from synthetic wastewater (5-25 mg/L) and 73.3 %-78.7 % from real uranium mine wastewater, achieving removal kinetics 2.8-5.5 times faster than those of Fe(0)-microbe mixed systems. At the same time, the system delivered power outputs of 0.136 W and 0.109 W for synthetic and real wastewater, respectively. Mechanistic analyses indicated that U immobilization was driven by microbial bioreduction and phosphate biomineralization, leading to the formation of uranyl phosphate and non-crystalline U(IV) precipitates. Biofilms enriched with electroactive and metal-reducing bacteria played a central role in U(VI) reduction, supported by functional genes associated with direct electron transfer (c-type cytochromes, e-pili), mediated electron transfer (flavins, phenazines), intracellular redox regulation (thioredoxin), and energy metabolism, indicating that U(VI) reduction proceeded through integrated extracellular, periplasmic, and cytoplasmic pathways. This work offers a promising and cost-effective strategy for sustainable uranium recovery from contaminated wastewater.