Assessment of heavy metal toxicity in soils contaminated by a former Pb–Zn mine and tailings management using flotation process, Jebel Ghozlane, Northern Tunisia

Abstract

The present work aims to investigate the toxicity of heavy metals in soil samples collected from the vicinity of the former Pb–Zn mine of Jebel Ghozlane and to evaluate reprocessing performances of mine tailings. The research was undertaken using two ecotoxicity tests: (1) MetPAD™ biotest Kit and (2) standardized germination test using wheat seeds (Triticum durum). Water extraction test was carried out to evaluate the potential availability of Pb, Zn and Cd in soil samples. Although their total levels in soil were found to be high, their water extracted values were relatively low (Pb 7–100 µg L−1, Zn 15–238 µg L−1 and Cd 1–5 µg L−1). The high germination percentages (GPs) of wheat seeds indicate that all soil samples tested are not toxic. However, the toxicity of soil–water extracts, as determined by MetPAD™ biotest which is specific for heavy metal toxicity, showed that two of six soil samples exhibited moderate toxicity. The toxicity was related to the relatively high concentrations of water-extractable Zn, Pb and Cd in these two samples. Laboratory flotation tests were used to evaluate the separation ability of Pb and Zn minerals from the mine tailings materials. Results showed that this method allows satisfactory reduction of Pb (95% recovery) and, to a less extent, of Zn (42% recovery) from mine tailings, that could be used as a mitigation strategy for heavy-metal contaminated soil.