wcm.04.2025.653.665

Acid Mine Drainage (AMD) is a persistent environmental issue in coal mining regions, characterized by high acidity and elevated dissolved metal concentrations. Overburden materials play a key role in AMD generation, particularly in the coal-bearing Sawahlunto Formation of the Ombilin Basin, West Sumatra. This study aimed to evaluate the AMD potential of various overburden rock samples through column leaching tests and to assess the neutralization performance of a vertical passive fixed-bed system using different alkaline materials. Leaching tests classified the overburdens of Kandi, Batu Tanjung, and Sikalang as Non-Acid Forming (NAF) with Net Acid Producing Potential (NAPP) values of –0.49, –3.74, and –0.04 kg H₂SO₄/ton, respectively. In contrast, the overburdens of Salak 1, Salak 2, and Salak 3 were Potentially Acid Forming (PAF) with NAPP values of 8.87, 0.25, and 0.76 kg H₂SO₄/ton. Column leaching experiments using selected samples packed in a fixed bed and fed with water at pH 8.5 yielded average effluent pH values of 6.26 (Kandi), 3.54 (Salak 1), and 6.10 (Batu Tanjung), with corresponding total dissolved solids of 442 ppm, 731.4 ppm, and 149 ppm. Neutralization tests using CaO and Silungkang and Kubang limestones produced effluent pH values ranging from 5 to 12.4, with calcium conversions of 23.98%, 47.4%, and 27.77%, respectively. The results indicate that AMD generation is strongly influenced by the mineralogical composition of the overburden, while neutralization performance varies with the type and reactivity of the alkaline medium. System design optimization considering bed height, particle size, and flow rate is recommended to achieve effective AMD control. Further scaling-up studies are essential to ensure the sustainable application of passive neutralization systems in coal mining operations, particularly in sump water treatment.