Enhanced Removal of Heavy Metals from Acid Mine Drainage Using Alkali-Leached Fly Ash as a Modified Adsorbent

Abstract

Acid mine drainage (AMD) is a major environmental concern characterized by low pH and elevated concentrations of heavy metals such as iron and manganese, requiring effective and sustainable treatment methods. This study investigates the use of industrial fly ash waste as a low-cost adsorbent, enhanced through alkali-leaching modification to produce a zeolite-like material with improved adsorption performance. The novelty of this work lies in the application of alkali-leached fly ash to simultaneously enhance adsorption capacity and neutralization ability for AMD treatment. Adsorbent characterization was conducted using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) analyses. BET results showed that modification significantly increased the specific surface area (14 m²/g) and pore volume (0.025 cm³/g). SEM-EDX results revealed a predominantly spherical morphology and changes in elemental composition following modification. XRD analysis showed partial dissolution of minor phases during alkali leaching, resulting in increased dominance of the quartz (SiO₂) phase with a main peak at 2θ = 26.59°. Batch adsorption experiments were performed under varying adsorbent dosages (10–100 g) to evaluate metal removal and pH improvement. The results demonstrated that modified fly ash increased AMD pH from 3.45 to 7.21 and achieved high removal efficiency of Mn, reducing its concentration to 0.05 mg/L (removal efficiency > 95%). Compared to untreated fly ash, the modified adsorbent exhibited significantly enhanced performance. The treated AMD met Indonesian Class I water quality standards. These findings highlight the potential of alkali-leached fly ash as an effective and sustainable adsorbent for AMD remediation.