<p>This study investigated the acid rock drainage (ARD) potential of waste rocks (WR) in two abandoned mines in the Ekurhuleni region of the Gauteng Province, South Africa. ARD prediction characterization and techniques such as mineralogy, maximum potential acidity (MPA), net acid production potential (NAPP), acid neutralizing capacity (ANC), net acid generation (NAG) and biokinetic tests were performed to assess the ARD formation potential of the WR samples. WR-1 and 2 had sulphur contents of 0.34 and 2.3%, respectively, and WR-2 was observed to have the highest MPA, NAPP and NAG per H₂SO₄ per ton, showing that it has an increased potential to produce acid compared to WR-1. WR-1 had the highest quantity of inert and acid-consuming minerals at 59.5 and 38.23&#xa0;wt%, respectively. The NAG pH vs NAPP plot supported that WR-2 had the highest potential to produce acidic conditions greater than the acid neutralization capacity (ANC). The higher the MPA, NAPP and NAG with a single sample, the greater the potential of ARD formation. This observation was further confirmed by the biokinetic tests which demonstrated that WR-2 had greater potential to form ARD. Therefore, this study showed that the waste rocks from the abandoned mines have a potential of forming ARD.</p>