Assessment of metals pollution in sediments and tailings of Klein Aub and Oamites mine sites, Namibia

Abstract

The environmental challenges posed by huge volumes of tailings and tailings dumps are often overshadowed by the economic benefits of mining. Tailings contain harmful quantities of toxic substances that can potentially pose serious health and environmental problems through air dispersion of air-dried tailings, leaching of potentially toxic chemical species, erosion and uptake by the aquatic system and bioaccumulation. The objective of this study was to determine the concentrations of investigated metals (Cr, Cu, Mn, Ni, Pb, Sr, V, Zn, Zr, Rb, Ba, Ca, Fe, K, S and Ti) and assess the pollution and contamination of sediments and tailings from Klein Aub and Oamites mine sites. Klein Aub was a copper mine (chalcocite) and Oamites mined chalcopyrite (Cu), bornite and gold as a byproduct of copper blisters. A total of 58 sediments and tailings samples were collected between January 2018 to January 2019 and analyzed using potable X-ray Fluorescence (XRF). Total concentrations showed high levels of crustal elements and heavy metals, particularly Cu, Zn, Ni and Pb in tailings. These toxic elements have a potential to cause serious human health and environmental impacts through leaching, erosion, air dispersion of tailings, etc. Pollution indices such as geo-accumulation, enrichment factor, contamination factor and PLI were used to assess the extent and degree of contamination. The Geo-accumulation index indicated that all tailings dams in both areas were moderately polluted with Cu, which recorded the highest Igeo values, above 1 but below 2. Sediments samples in both sites recorded Igeo values below 1, suggesting that the quality of sediments is unpolluted to moderately polluted. All tailings dams recorded an EF ≥ 40 for Cu, with the overall highest value in Klein Aub, all of which is indicative of an extremely high enrichment from non-crustal sources. This enrichment was attributed to the primary and secondary mineral ores. The pollution in Oamites tailings was minimal compared to the Klein Aub tailings, owing to the fact that the tailings dams at Oamites are capped. However, the enrichment factor of the sediments at Oamites suggests that the streams are polluted possibly through leaching, erosion and/or seepage. The HPI value for the Klein Aub tailings indicates that the tailings were considerably polluted. Therefore, precautionary measures should be considered for the Klein Aub tailings dam to prevent contamination or pollution of the surrounding environment.