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Dzinomwa G, Mapani B, Nghipulile T, Maweja K, Kurasha JT, Amwaama M, Chigayo K. Mineralogical Characterization of Historic Copper Slag to Guide the Recovery of Valuable Metals: A Namibian Case Study. Materials (Basel) 2023; 16:6126. [PMID: 37763403 PMCID: PMC10532964 DOI: 10.3390/ma16186126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Revised: 08/25/2023] [Accepted: 08/26/2023] [Indexed: 09/29/2023]
Abstract
The depletion of the ore reserves in the world necessitates the search for secondary sources such as waste products (tailings and slag). The treatment and cleaning up of such secondary sources also has a positive impact on the environment. A smelter in Namibia we examined had historic slag which accumulated over decades of its operating life, thus posing the challenge of how best to collect representative samples to evaluate and propose viable methods of recovering contained metals. In this study, analytical and mineralogical characterization of the slag was performed using X-ray fluorescence (XRF) analysis, atomic absorption spectrometer (AAS), ICP-OES, scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) analysis, and optical microscopy analysis. The chemical analyses showed that the metal values contained in the slag were mainly copper, lead, and zinc whose average contents were approximately 0.35% Cu, 3% Pb, and 5.5% Zn. About 10.5% Fe was also contained in the slag. Germanium was detected by scanning electron microscopy, but was however below detection limits of the chemical analysis equipment used. Based on the results, approximate conditions under which the different slag phases were formed were estimated and the recovery routes for the various metals were proposed. Analysis by both optical and scanning electron microscopy revealed that Zn and Fe occurred mainly in association with O as oxides, while Cu and Pb were mainly associated with S as sulphides. The slag consisted of three different phases, namely the silicate phase (slag), metallic phase and the sulphide phases. The phases in the slag were mainly silicate phases as well as metallic and sulphide phases. It was observed that the metallic and sulphide phases were dominant in the finer size fractions (-75 µm) whereas the sulphide phase was also present in the coarser size fractions (+300 µm). An important finding from the microscopy examination was that the sulphide phases were interstitial and could be liberated from the slag. This finding meant that liberation and subsequent concentration of the sulphide phases was feasible using conventional processing techniques.
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Affiliation(s)
- Godfrey Dzinomwa
- Department of Civil, Mining, and Process Engineering, Faculty of Engineering and the Built Environment, Namibia University of Science and Technology, Private Bag, Windhoek 13388, Namibia; (B.M.); (K.M.); (J.T.K.); (M.A.); (K.C.)
| | - Benjamin Mapani
- Department of Civil, Mining, and Process Engineering, Faculty of Engineering and the Built Environment, Namibia University of Science and Technology, Private Bag, Windhoek 13388, Namibia; (B.M.); (K.M.); (J.T.K.); (M.A.); (K.C.)
| | - Titus Nghipulile
- Minerals Processing Division, Mintek, Private Bag X3015, Randburg 2125, South Africa;
| | - Kasonde Maweja
- Department of Civil, Mining, and Process Engineering, Faculty of Engineering and the Built Environment, Namibia University of Science and Technology, Private Bag, Windhoek 13388, Namibia; (B.M.); (K.M.); (J.T.K.); (M.A.); (K.C.)
| | - Jaquiline Tatenda Kurasha
- Department of Civil, Mining, and Process Engineering, Faculty of Engineering and the Built Environment, Namibia University of Science and Technology, Private Bag, Windhoek 13388, Namibia; (B.M.); (K.M.); (J.T.K.); (M.A.); (K.C.)
| | - Martha Amwaama
- Department of Civil, Mining, and Process Engineering, Faculty of Engineering and the Built Environment, Namibia University of Science and Technology, Private Bag, Windhoek 13388, Namibia; (B.M.); (K.M.); (J.T.K.); (M.A.); (K.C.)
| | - Kayini Chigayo
- Department of Civil, Mining, and Process Engineering, Faculty of Engineering and the Built Environment, Namibia University of Science and Technology, Private Bag, Windhoek 13388, Namibia; (B.M.); (K.M.); (J.T.K.); (M.A.); (K.C.)
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Tabares X, Zimmermann H, Dietze E, Ratzmann G, Belz L, Vieth‐Hillebrand A, Dupont L, Wilkes H, Mapani B, Herzschuh U. Vegetation state changes in the course of shrub encroachment in an African savanna since about 1850 CE and their potential drivers. Ecol Evol 2020; 10:962-979. [PMID: 32015858 PMCID: PMC6988543 DOI: 10.1002/ece3.5955] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2019] [Revised: 11/10/2019] [Accepted: 12/05/2019] [Indexed: 11/30/2022] Open
Abstract
Shrub encroachment has far-reaching ecological and economic consequences in many ecosystems worldwide. Yet, compositional changes associated with shrub encroachment are often overlooked despite having important effects on ecosystem functioning.We document the compositional change and potential drivers for a northern Namibian Combretum woodland transitioning into a Terminalia shrubland. We use a multiproxy record (pollen, sedimentary ancient DNA, biomarkers, compound-specific carbon (δ13C) and deuterium (δD) isotopes, bulk carbon isotopes (δ13Corg), grain size, geochemical properties) from Lake Otjikoto at high taxonomical and temporal resolution.We provide evidence that state changes in semiarid environments may occur on a scale of one century and that transitions between stable states can span around 80 years and are characterized by a unique vegetation composition. We demonstrate that the current grass/woody ratio is exceptional for the last 170 years, as supported by n-alkane distributions and the δ13C and δ13Corg records. Comparing vegetation records to environmental proxy data and census data, we infer a complex network of global and local drivers of vegetation change. While our δD record suggests physiological adaptations of woody species to higher atmospheric pCO2 concentration and drought, our vegetation records reflect the impact of broad-scale logging for the mining industry, and the macrocharcoal record suggests a decrease in fire activity associated with the intensification of farming. Impact of selective grazing is reflected by changes in abundance and taxonomical composition of grasses and by an increase of nonpalatable and trampling-resistant taxa. In addition, grain-size and spore records suggest changes in the erodibility of soils because of reduced grass cover. Synthesis. We conclude that transitions to an encroached savanna state are supported by gradual environmental changes induced by management strategies, which affected the resilience of savanna ecosystems. In addition, feedback mechanisms that reflect the interplay between management legacies and climate change maintain the encroached state.
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Affiliation(s)
- Ximena Tabares
- Alfred Wegener InstituteHelmholtz Centre for Polar and Marine ResearchPotsdamGermany
- Institute of Biochemistry and BiologyPotsdam UniversityPotsdamGermany
| | - Heike Zimmermann
- Alfred Wegener InstituteHelmholtz Centre for Polar and Marine ResearchPotsdamGermany
| | - Elisabeth Dietze
- Alfred Wegener InstituteHelmholtz Centre for Polar and Marine ResearchPotsdamGermany
| | | | - Lukas Belz
- Institute for Chemistry and Biology of the Marine EnvironmentCarl von Ossietzky University of OldenburgOldenburgGermany
| | | | - Lydie Dupont
- MARUM – Centre for Marine Environmental SciencesUniversity of BremenBremenGermany
| | - Heinz Wilkes
- Institute for Chemistry and Biology of the Marine EnvironmentCarl von Ossietzky University of OldenburgOldenburgGermany
| | | | - Ulrike Herzschuh
- Alfred Wegener InstituteHelmholtz Centre for Polar and Marine ResearchPotsdamGermany
- Institute of Biochemistry and BiologyPotsdam UniversityPotsdamGermany
- Institute of Environmental Science and GeographyPotsdam UniversityPotsdamGermany
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Grösslová Z, Vaněk A, Oborná V, Mihaljevič M, Ettler V, Trubač J, Drahota P, Penížek V, Pavlů L, Sracek O, Kříbek B, Voegelin A, Göttlicher J, Drábek O, Tejnecký V, Houška J, Mapani B, Zádorová T. Thallium contamination of desert soil in Namibia: Chemical, mineralogical and isotopic insights. Environ Pollut 2018; 239:272-280. [PMID: 29656251 DOI: 10.1016/j.envpol.2018.04.006] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2018] [Revised: 03/29/2018] [Accepted: 04/01/2018] [Indexed: 06/08/2023]
Abstract
We studied arid desert soils from Namibia (Rosh Pinah) that were contaminated with up to 7 mg kg-1 of thallium (Tl) via dust emitted from a local flotation tailing dam. Chemical extractions of waste and soil materials indicated that most of the Tl is strongly bound, in accordance with X-ray diffraction and X-ray absorption spectroscopy data that point to the predominant association of Tl with metal sulfides and phyllosilicates. The isotope fractionation factor ε205Tl of the soil samples (from -0.4 to +3.8) shows a positive linear relationship (R2 = 0.62) with 1/Tl, indicative for the mixing of two major Tl pools, presumably anthropogenic Tl and geogenic Tl. The ε205Tl value for the topmost soil samples (∼+3) closely matches the ε205Tl value for post-flotation waste particles with a diameter of <0.05 mm, whereas the bulk flotation waste exhibits a significantly larger ε205Tl value (∼+6). These variations are in accordance with predominant atmospheric transfer of Tl from the tailings to the adjacent soils via fine (dust) particles. The identified minimal Tl alteration in soils indicates that only a small part of the Tl could be potentially released and passively enter the vegetation, local population and/or food chain in the long term. From this viewpoint, Tl does not represent such an important environmental concern as other (abundant) contaminants at the locality. Furthermore, there could be a relevance for other alkaline desert soils, including those where Tl pollution plays a major role.
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Affiliation(s)
- Zuzana Grösslová
- Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kamýcká 129, 165 00, Prague 6, Czech Republic
| | - Aleš Vaněk
- Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kamýcká 129, 165 00, Prague 6, Czech Republic.
| | - Vendula Oborná
- Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kamýcká 129, 165 00, Prague 6, Czech Republic
| | - Martin Mihaljevič
- Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, 128 43, Prague 2, Czech Republic
| | - Vojtěch Ettler
- Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, 128 43, Prague 2, Czech Republic
| | - Jakub Trubač
- Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, 128 43, Prague 2, Czech Republic
| | - Petr Drahota
- Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, 128 43, Prague 2, Czech Republic
| | - Vít Penížek
- Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kamýcká 129, 165 00, Prague 6, Czech Republic
| | - Lenka Pavlů
- Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kamýcká 129, 165 00, Prague 6, Czech Republic
| | - Ondra Sracek
- Department of Geology, Faculty of Science, Palacký University, 17. Listopadu 12, 771 46, Olomouc, Czech Republic
| | - Bohdan Kříbek
- Czech Geological Survey, Geologická 6, 152 00, Prague 5, Czech Republic
| | - Andreas Voegelin
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, CH-8600, Duebendorf, Switzerland
| | - Jörg Göttlicher
- Institute for Photon Science and Synchrotron Radiation, Karlsruhe Institute of Technology, KIT Campus North, Hermann-von-Helmholtz-Platz 1, D-76344, Eggenstein-Leopoldshafen, Germany
| | - Ondřej Drábek
- Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kamýcká 129, 165 00, Prague 6, Czech Republic
| | - Václav Tejnecký
- Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kamýcká 129, 165 00, Prague 6, Czech Republic
| | - Jakub Houška
- Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kamýcká 129, 165 00, Prague 6, Czech Republic
| | - Benjamin Mapani
- Department of Geology, Faculty of Science, University of Namibia, Private Bag, 13301, Windhoek, Namibia
| | - Tereza Zádorová
- Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kamýcká 129, 165 00, Prague 6, Czech Republic
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Sracek O, Mihaljevič M, Kříbek B, Majer V, Filip J, Vaněk A, Penížek V, Ettler V, Mapani B. Geochemistry of mine tailings and behavior of arsenic at Kombat, northeastern Namibia. Environ Monit Assess 2014; 186:4891-4903. [PMID: 24691736 DOI: 10.1007/s10661-014-3746-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Accepted: 03/18/2014] [Indexed: 06/03/2023]
Abstract
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 (57)Fe 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.
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Affiliation(s)
- O Sracek
- Department of Geology, Faculty of Science, Palacký University, Olomouc, Czech Republic,
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