Nitrogen-Rich Organic Matter Formation and Stabilization in Iron Ore Tailings: A Submicrometer Investigation

Organicmatter (OM) formation and stabilization are critical processesin the eco-engineered pedogenesis of Fe ore tailings, but the underlyingmechanisms are unclear. The present 12 month microcosm study has adoptednanoscale secondary ion mass spectrometry (NanoSIMS) and synchrotron-basedscanning transmission X-ray microscopy (STXM) techniques to investigateOM formation, molecular signature, and stabilization in tailings atmicro- and nanometer scales. In this system, microbial processingof exogenous isotopically labeled OM demonstrated that C-13 labeled glucose and C-13/N-15 labeled plantbiomass were decomposed, regenerated, and associated with Fe-richminerals in a heterogeneous pattern in tailings. Particularly, whentailings were amended with plant biomass, the N-15-richmicrobially derived OM was generated and bound to minerals to forman internal organo-mineral association, facilitating further OM stabilization.The organo-mineral associations were primarily underpinned by interactionsof carboxyl, amide, aromatic, and/or aliphatic groups with weatheredmineral products derived from biotite-like minerals in fresh tailings(i.e., with Fe2+ and Fe3+) or with Fe3+ oxyhydroxides in aged tailings. The study revealed microbial OMgeneration and subsequent organo-mineral association in Fe ore tailingsat the submicrometer scale during early stages of eco-engineered pedogenesis,providing a basis for the development of microbial based technologiestoward tailings' ecological rehabilitation. Microbially derived organic matter wasformed and associatedwith weathered products of primary minerals in iron ore tailings undergoingeco-engineered pedogenesis.