A re-assessment of metal pollution in the Dexing mining area in Jiangxi province, China: current status, hydro-geochemical controls, and effectiveness of remediation practices

This study re-assess the environmental impacts of the Dexing copper mine (the largest open-pit copper mine in Asia) on the Lean river and its two tributaries (the Dawu river and Jishui river) in the Jiangxi province, China, with particular focus on metal pollution as well as the effectiveness and side-effects of remediation activities. Results show that the Dawu river and its mixing zone with the Lean river were still heavily influenced by acid mine drainage (AMD) and loaded with elevated levels of metals, in particular Mn, Ni, and Al whose concentrations were frequently above the health-based guideline values. Manganese and Ni in the AMD-impacted waters were predicted to occur as free ions or sulfate and carbonate complexes, and thus highly-toxic to living organisms. Although Al in the AMD-impacted waters was predicted to exist largely as colloidal hydroxides with low bioavailability, abundant formation of such nano-sized particles could impair the respiratory and circulatory systems of aquatic macro-invertebrates. The integration and comparison of the results from the current and previous studies show that the concentrations of several metals (Cu, Zn, and Cd) in the Dawu river decreased significantly after 2011–2012, during which several remediation practices were implemented (e.g., AMD neutralization, excavation of contaminated sediments in impounded rivers, and rehabilitation of mine tailings and open-pit slopes). This provides evidence that these remediation practices have effectively limited the dispersion of metals from the mining area. However, AMD neutralization greatly enhanced the release of sulfate, making the mining area an even more important sulfate source.