pH-controlled mobility of heavy metals in bio-oxidation (BIOX) gold mine tailings from Obuasi, Ghana

Mining tailings represent long-term environmental liabilities because they can release toxic metals into surrounding ecosystems. This study investigated the concentration and mobility of selected heavy metals in bio-oxidation (BIOX→) gold mine tailings from the Sansu Sulphide Treatment Plant, Obuasi, Ghana. Total metal concentrations were determined using Atomic Absorption Spectrophotometry and leaching behaviour was evaluated under controlled pH conditions over a ten-week period. The tailings were strongly enriched in iron and arsenic relative to other metals. Leaching experiments showed pronounced pH-dependent behaviour: acidic conditions promoted progressive release of all analysed metals, whereas alkaline conditions significantly reduced dissolved concentrations through precipitation reactions. Detectable but low concentrations were also observed in neutral water, indicating potential long-term leaching even without strong acidification. The results demonstrate that heavy metal mobility in BIOX→ tailings is controlled primarily by pH and oxidation processes. Arsenic represents the greatest environmental concern due to its abundance and mobility under acidic conditions. Maintaining alkaline conditions in tailings storage facilities is therefore critical to minimize groundwater contamination risk in gold mining environments.