Incurred environmental risks and potential contamination sources in an abandoned mine site

Abstract

The mineralogical characterization of Fedj Lahdoum mine wastes measured by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) showed the presence of the following sulfide minerals: galena (PbS), sphalerite (ZnS), pyrite (FeS₂), cerussite (PbCO₃) and smithsonite (ZnCO₃). The wastes were stored in tailing ponds. The results showed that the concentration of metals from tailings were up to 10 460 mg.kg^-1 for total Zn, 2 100 mg.kg^-1 for total Pb and 62.08 mg.kg^-1 for total Cd. The tailings have presented a fine unconsolidated texture that accelerated the dispersion of the particles rich in heavy metals. Geochemical analysis of soil has revealed high total contents of Pb, Zn and Cd, respectively: 3 646, 3 236 and 17 mg.kg^-1. Chemical analysis of cultivated and wild plants species inside the district contain high grades in heavy metals: 708.56 mg Zn. kg^-1; 16.24 mg Pb.kg^-1 (Thymus vulgaris (L)); 500.44 mg Zn. kg^-1, 12.44 mg Pb. kg^-1 (Laurus nobilis (L)); 128.33 mg Zn. kg^-1 and 22.53 mg Pb.kg^-1 (Ficus (L)) and 106.73 mgZn.kg^-1 (pimento). The high levels detected in soil and plants have exceeded the Tunisian and Canadian standards. These results showed that the abandoned site was contaminated by the presence of tailing dumps which were exposed to significant water and/or wind erosion. To solve this problem, we proposed an environmental desulphurization by froth flotation.

Keywords: Heavy metals, mine tailings, abandoned mining-district, plant contamination.