Mechanistic Study on Organo-Mineral Complexes During Pedogenesis in Iron Tailings

Contemporary mine restoration faces challenges in achieving self-sustaining ecosystems. Accelerating pedogenesis within iron tailings offers a promising strategy by fostering organic carbon (OC) stabilization and soil structure development via organo-mineral complex formation. This study elucidated the microscale mechanisms governing exogenous OC fixation at mineral interfaces in iron tailings during simulated pedogenesis. Controlled microcosm experiments employed iron tailings of sandy and loam textures amended with farmyard manure (F), Mollisols (M), or their combination (FM), alongside original iron tailings as a control. Over 160 days, we tracked OC fractionation, Fe/Al oxide dynamics and mineralogical evolution. Key findings revealed that FM treatment induced the most significant OC accumulation, increasing total OC by 163% (loam) and 108% (sand), with MOC exhibiting the largest relative surge (455% loam, 217% sand). This coincided with pronounced increases in reactive Fe/Al oxides, particularly oxalate-extractable Fe (Feox; +230% loam, +212% sand) and pyrophosphate-extractable Al (Alp; +122% loam, +54% sand). Mineralogical characterization (XRD) demonstrated distinct phase transformations in amended tailings (e.g., formation of anorthite, grunerite, ankerite), indicative of accelerated weathering. XPS analysis confirmed the presence of surface Fe3+/Fe2+ species and suggested Al-O-C bonding. These reactive secondary phases, characterized by high specific surface area, facilitated robust OC sequestration primarily through MOC formation. The synergistic input of farmyard manure and Mollisols proved most effective in driving these processes, particularly in loam-textured tailings. Our results provide novel mechanistic insights into Fe/Al-OC association dynamics during tailings pedogenesis. This understanding underpins strategies for enhancing in situ soil formation in iron tailings, ultimately promoting sustainable ecological restoration of mine-degraded landscapes.