ABSTRACT Efficient manganese (Mn) removal from acidic mine drainage (AMD) is challenging due to its high solubility and slow oxidation kinetics. We investigate a mechanism that enables the efficient removal of Mn in a sand filter at an operational AMD treatment facility, with particular emphasis on naturally formed Mn oxides on sand grain surfaces (Mn‐precipitated sand; MPS). Characterization of the filter media using x‐ray fluorescence, x‐ray diffraction, scanning electron microscopy, and transmission electron microscopy identified a coating of poorly crystalline birnessite (δ‐MnO 2 ) that formed in situ on the MPS and is absent on unprecipitated sand (UNS). X‐ray absorption near‐edge structure spectroscopy confirmed that this coating is composed mainly of tetravalent Mn(IV). Batch experiments simulating filtration conditions were performed to compare Mn removal kinetics using MPS, UNS, and commercial Mn oxide powder from thickener mine water and pure water with 2 mg/L dissolved Mn 2+ . The MPS removed > 99% of the dissolved Mn within 3 h from both mine and pure water, whereas UNS only removed some Mn ( 96% removal. These findings reveal that Mn removal is driven by abiotic autocatalysis on a naturally formed, Mn(IV)‐rich birnessite coating. The high efficiency of this process at a neutral pH presents a significant opportunity to optimize AMD treatment by lowering operational pH and reducing chemical consumption and sludge production for a more sustainable remediation strategy.
Godirilwe et al. (Thu,) studied this question.