This study investigated the synthesis and adsorption performance of activated carbon derived from coconut fronds for the removal of iron (Fe) and manganese (Mn) from acid mine drainage (AMD). The adsorbent was prepared by chemical activation with hydrochloric acid (HCl), followed by thermal activation at 923 K. Physicochemical characterization included proximate analysis, Brunauer–Emmett–Teller (BET) surface area, iodine value, pore structure analysis, and Fourier Transform Infrared (FTIR) spectroscopy. The activated carbon exhibited a high fixed carbon content (75.9%), a BET surface area of 394.78 m² g⁻¹, an average pore diameter of 6.91 nm, and an iodine value of 1130.26 mg g⁻¹, indicating a well-developed porous structure. FTIR analysis confirmed the presence of oxygen-containing functional groups, particularly C–O, which contribute to the adsorption of metal ions. The researcher experiments with batch adsorption using modified acid mine drainage with Fe and Mn concentrations of 300–600 mg L⁻¹ and contact times of 10–80 min. The equilibrium data were better described by the Freundlich isotherm model, with R² values of 0.937 for Fe and 0.955 for Mn, indicating multilayer adsorption on heterogeneous surfaces. The maximum adsorption capacities were 95.85 mg g⁻¹ for Fe and 9.31 mg g⁻¹ for Mn. The kinetic analysis followed a pseudo-second-order model. The researcher achieved removal efficiencies of 83.33% for Fe and 66.88% for Mn, demonstrating the strong potential of coconut frond-based activated carbon as a low-cost adsorbent for AMD treatment.