Acid mine drainage from mine tailings at Selebi Phikwe, eastern Botswana, has been investigated using a combination of total decomposition, sequential extraction, X-ray diffraction, Mössbauer spectroscopy, and SEM analyses of solid phase samples, water analyses, isotopic analyses, and geochemical modeling. The principal ferric phases in the seepage stream sediments are jarosite and goethite, which incorporate Ni and Cu. The Mössbauer spectroscopy (MS) indicated exclusively 3+ oxidation state of iron with typical features of ferric hydroxides/sulfates. A fraction of dissolved sulfate is also sequestered in gypsum which precipitates further downstream. Significant portions of Fe, Ni, and Cu are transported in suspension. Values of pH decreased downstream due to H+ generated by the precipitation of jarosite. Values of δ2H and δ18O indicate evaporation of pore water in the mine tailings before seepage. Values of δ34S(SO4) are consistent with the oxidation of sulfides, but sample from the seepage face is affected by dissolution of gypsum. No minerals of Ni and Cu were detected and the principal attenuation processes seem to be adsorption and co-precipitation with jarosite. Higher contents of Cu are sequestered in solid phases compared to Ni, in spite of much higher dissolved Ni concentrations. Based on the speciation calculations, seepage water is undersaturated with respect to all Ni and Cu phases and adsorption and co-precipitation with jarosite seems to be the principal attenuation processes. Direct geochemical modeling was able to reproduce downstream pH trends, thus confirming the precipitation of jarosite as the principal pH-controlling process.

• Keywords
• Attenuation, Cu, Jarosite, Mine tailings, Ni, Ochres, Seepage,
• MeSH
• Adsorption MeSH
• Water Pollutants, Chemical analysis   chemistry   MeSH
• Models, Chemical * MeSH
• X-Ray Diffraction MeSH
• Mining * MeSH
• Hydrogen-Ion Concentration MeSH
• Copper analysis   chemistry   MeSH
• Minerals MeSH
• Environmental Monitoring methods   MeSH
• Nickel analysis   chemistry   MeSH
• Industrial Waste analysis   MeSH
• Sulfates MeSH
• Iron Compounds MeSH
• Sulfides analysis   MeSH
• Ferric Compounds MeSH
• Iron analysis   MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Botswana MeSH
• Names of Substances
• Water Pollutants, Chemical MeSH
• ferric hydroxide MeSH Browser
• ferric sulfate MeSH Browser
• goethite MeSH Browser
• jarosite MeSH Browser
• Copper MeSH
• Minerals MeSH
• Nickel MeSH
• Industrial Waste MeSH
• Sulfates MeSH
• Iron Compounds MeSH
• Sulfides MeSH
• Ferric Compounds MeSH
• Iron MeSH