Geochemistry of mine tailings and behavior of arsenic at Kombat, northeastern Namibia
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The mine tailings at Kombat, in semiarid northeastern Namibia, were investigated by the combination of solid-phase analyses, mineralogical methods, leaching tests, and speciation modeling. Dissolution of the most abundant primary sulfides, chalcopyrite and galena, released copper and lead which were adsorbed onto ferric oxyhydroxides or precipitated in the form of malachite, Cu2CO3(OH)2, and cerussite, PbCO3, respectively. Arsenic released from arsenopyrite was incorporated into ferric oxyhydroxides. Based on sequential extraction and 57Fe Mössbauer spectroscopy, a large amount of ferric iron is present as low solubility hematite and goethite formed rapidly (<10 years) under warm semiarid climatic conditions, and arsenic in these phases is relatively tightly bound. It seems that Cu and especially Pb in carbonate minerals represent a more serious environmental risk. Immobilization of As in hematite has implications for other mining sites in regions with similar climatic conditions because this process results in long-term immobilization of As.
KeywordsMine tailings Namibia Neutralization Arsenic Hematite
Funding for this study was provided by the Czech Science Foundation (GAČR P210/12/1413), and Ministry of Education, Youth and Sports of the Czech Republic (MSM0021620855). The authors also acknowledge the support by the Operational Program Research and Development for Innovations—European Development Fund (CZ.1.05/2.1.00/03.0058) of the Ministry of Education, Youth and Sports of the Czech Republic. This study was carried out within the framework of the IGCP Project No. 594 (“Assessment of impact of mining and mineral processing on the environment and human health in Africa”). We thank two anonymous reviewers, whose comments helped to improve the manuscript.
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