Liquid waste containing heavy metals must be treated before being released into the environment. This study investigated the potential of coal-derived activated carbon as an adsorbent in AMD (Acid Mine Drainage) treatment. Coal was activated with H3PO4 with five weight ratios (10%, 20%, 30%, 40%, and 50%), carbonized for 120 min at 650 °C, and subjected to the proximate analysis of activated carbon. The results showed that the water content, ash content, volatile matter content, and fixed carbon were generally in accordance with Indonesian standards (SNI). The results of FT-IR and SEM on BET surface area and total pore volume of activated carbon were 296.4 m2/g and 0.1562 cc/g, respectively, indicative of sizeable pores, cracks, channels, and active groups. The iodine outnumbered the minimum limit in the SNI, and the activated carbon quantity consistently increased with H3PO4 ratios. The iodine produced with 10%, 20%, 30%, 40%, and 50% H3PO4 was 956.95 mg/g, 967.13 mg/g, 1,221.63 mg/g, 1,206.346 mg/g, and 865.32 mg/g., respectively.