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Minerals 2018, 8(2), 64; https://doi.org/10.3390/min8020064

Mobility and Attenuation Dynamics of Potentially Toxic Chemical Species at an Abandoned Copper Mine Tailings Dump

1
Environmental Remediation and Water Pollution Chemistry Group, School of Environmental Sciences, University of Venda, Private Bag X5050, Thohoyandou, Limpopo 0950, South Africa
2
Department of Ecology and Resources Management, University of Venda, Private Bag X5050, Thohoyandou, Limpopo 0950, South Africa
3
Department of Geology and Applied Geophysics, Ekiti State University, Ado Ekiti P.M.B. 5363, Nigeria
*
Author to whom correspondence should be addressed.
Received: 18 December 2017 / Revised: 24 January 2018 / Accepted: 5 February 2018 / Published: 12 February 2018
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Abstract

Large volumes of disposed mine tailings abound in several regions of South Africa, as a consequence of unregulated, unsustainable long years of mining activities. Tailings dumps occupy a large volume of valuable land, and present a potential risk for aquatic systems, through leaching of potentially toxic chemical species. This paper reports on the evaluation of the geochemical processes controlling the mobility of potentially toxic chemical species within the tailings profile, and their potential risk with regard to surface and groundwater systems. Combination of X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) techniques, show that the tailing profiles are uniform, weakly altered, and vary slightly with depth in both physical and geochemical properties, as well as mineralogical composition. Mineralogical analysis showed the following order of abundance: quartz > epidote > chlorite > muscovite > calcite > hematite within the tailings profiles. The neutralization of the dominant alumino-silicate minerals and the absence of sulfidic minerals, have produced medium alkaline pH conditions (7.97–8.37) at all depths and low concentrations of dissolved Cu (20.21–47.9 µg/L), Zn (0.88–1.80 µg/L), Pb (0.27–0.34 µg/L), and SO42− (15.71–55.94 mg/L) in the tailings profile leachates. The relative percentage leach for the potentially toxic chemical species was low in the aqueous phase (Ni 0.081%, Cu 0.006%, and Zn 0.05%). This indicates that the transport load of potentially toxic chemical species from tailings to the aqueous phase is very low. The precipitation of secondary hematite has an important known ability to trap and attenuate the mobility of potentially toxic chemical species (Cu, Zn, and Pb) by adsorption on the surface area. Geochemical modelling MINTEQA2 showed that the tailings leachates were below saturation regarding oxyhydroxide minerals, but oversaturated with Cu bearing mineral (i.e., cuprite). Most of the potentially toxic chemical species occur as free ions in the tailings leachates. The precipitation of secondary hematite and cuprite, and geochemical condition such as pH of the tailings were the main solubility and mobility controls for the potentially toxic chemical species, and their potential transfer from tailings to the aqueous phase. View Full-Text
Keywords: copper tailings dump; leaching; pH; mobility; chemical species; attenuation mechanisms; aquatic systems copper tailings dump; leaching; pH; mobility; chemical species; attenuation mechanisms; aquatic systems
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Gitari, W.M.; Thobakgale, R.; Akinyemi, S.A. Mobility and Attenuation Dynamics of Potentially Toxic Chemical Species at an Abandoned Copper Mine Tailings Dump. Minerals 2018, 8, 64.

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