Rhizosphere Drives Biotite-Like Mineral Weathering and Secondary Fe–Si Mineral Formation in Fe Ore Tailings

Pioneer plants play an important role in eco-engineering Fe ore tailings into soil for sustainable mine site rehabilitation. However, root-driven mineral weathering and secondary mineral formation remain poorly understood in tailings, despite being prerequisites for aggregate formation and pedogenesis. The present study aimed at characterizing the direct role of plant roots in tailing mineral weathering and secondary mineral formation in a compartmented cultivation system. It was found that root activities accelerated the weathering of biotite-like minerals via Fe(II) oxidation coupled with Fe(III) and Si dissolution. Numerous nanosized Fe–Si short-range-ordered (SRO) minerals and vermiculite were neoformed in the tailings after root interactions, as revealed by various microspectroscopic analyses. The Fe–Si-SRO minerals may have resulted from co-precipitation of dissolved Fe(III) and Si on mineral surfaces under alkaline and circumneutral pH conditions. Among the three plant species, Sorghum spp. (Gramineae plant) root developed most extensively in the tailings, possibly leading to more efficient mineral weathering and secondary mineral formation than Atriplex amnicola (halophyte plant) and Acacia chisholmii (leguminous plant). Overall, the study has elucidated the rhizosphere effects on tailing mineral (biotite dominant) weathering and secondary Fe–Si mineral formation, justifying pioneer plant roles in eco-engineering Fe ore tailings into soil.