Geochemical behavior and environmental implications of arsenic in roasted tailings from the Vatukoula Epithermal Gold Mine in Fiji.

The development of gold (Au) mines is expected to continue in the future due to increasing global demand for Au. However, arsenic (As), a problematic naturally occurring potentially toxic element, is often found associated with the gold deposits, which remains a critical concern. This study investigates the leaching dynamics of As, its adsorption mechanisms, and the risk of acidification at the Vatukoula Gold Mines in Fiji. Solid-phase partitioning, batch leaching, accelerated weathering tests, and thermodynamic modeling of leachates were employed to elucidate the As dynamics. The impact of roasting on mineral compositions and As adsorption dynamics in tailings were also assessed. Leaching tests showed that As concentrations in altered veins and tailings exceeded the WHO drinking water guideline of 10 µg/L but remained within Fiji's permissible limit of 50 µg/L. Sequential extraction demonstrated that As was primarily associated with sulfide and residual fractions in altered veins and tailings. Risks of acidification were identified in altered veins due to pyrite oxidation, whereas the host rocks and tailings showed no significant acidification potential. Roasting transformed pyrite into hematite and dolomite into calcite and periclase, influencing As mobility and maintaining weakly alkaline pH in the tailing dam. Iron oxides in tailings were found to adsorb As effectively, consistent with Henry adsorption isotherms. This was supported by thermodynamic modeling and electron probe microanalyzer (EPMA) observations, which confirmed the association of As with Fe oxides in tailings. This study provides critical insights into geochemical dynamics of As and environmental management of As-bearing epithermal gold mines.