Acid mine drainage (AMD) is characterized by high concentrations of Fe(II) and Fe(III), which can be harnessed for the in-situ formation of schwertmannite, enabling the efficient immobilization of toxic heavy metals. However, existing biological and chemical methods for schwertmannite synthesis face significant challenges, including low Fe(II) oxidation rates and particularly limited Fe(III) precipitation efficiency in acidic environments. In this study, we develop a visible light-assisted photo-electrochemical (PEC) system that effectively overcomes these barriers. By leveraging anodically evolved O