Environmental impact of ore smelting: the African & European experience Vojtěch ETTLER EGG – Environmental Geochemistry Group Institute of Geochemistry, Mineralogy and Mineral Resources Faculty of Science, Charles University in Prague Albertov 6, 128 43 Prague 2, Czech Republic
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Environmental impact of ore smelting: the African & European experience Vojtěch ETTLER EGG – Environmental Geochemistry Group Institute of Geochemistry,
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Environmental impactof ore smelting: the African & European experience
Vojtěch ETTLEREGG – Environmental Geochemistry GroupInstitute of Geochemistry, Mineralogy and Mineral ResourcesFaculty of Science, Charles University in PragueAlbertov 6, 128 43 Prague 2, Czech Republic
Number of colleagues and students:
Charles University in PragueMartin Mihaljevič, Ondřej Šebek, Ladislav Strnad, Jan Jehlička, Martina Vítková & many students
Czech Geological SurveyBohdan Kříbek, František Veselovský, Vladimír Majer
Université d´Orléans, FranceJean-Claude Touray, Patrick Baillif,…
People from Zambian & Namibian universities / geological surveys:B. Mapani, F. Kamona, I. Nyambe, G. Schneider,…
Number of companies:
Funding:• Czech Science Foundation (GAČR 210/12/1413)• Ministry of Education, Youth and Sports of the Czech Rep.• Granting Agency of the AS CR and Charles University• IGCP project No. 594 („Assessment of impact of mining and mineral processing on the environment and human health in Africa“)
Kovohutě Příbram CZ (Pb smelter)Zdeněk Kunický, Karel Vurm
Chambishi and Mufulira smelters (Zambia)Tony Gonzáles and technical staff
Background information
• non-ferrous metal smelting • large amounts of smelting waste
• silicate slag• fly ash – air polution control (APC) residues
• high concentrations of inorganic contaminants• high leachability of metals and metalloids• in EU classified as hazardous materials• soil pollution by smelter emissions (fly ash)
Outline of the presentation
• Examples from Czech and African smelting sites
• Long-term environmental stability of waste materials from the smelting activities (slags) – insights from mineralogy/geochemistry
• Fate of smelter-derived contamination in the environment (soils affected by smelter emissions)
Environmental stability of smelting slags
Slags are silicate waste products resulting from extraction of metals from ores by reducing
fusion. Slags contain high levels of contaminants.
Pb smelter(Příbram, CZ)
• operating 200 years • Pb-Ag production • processing of ores (1786-1974)• processing of car batteries since 1974
• 1.8 Mt of slags on the dumps
Slag melttipped off >>>
Reducing fusion in shaft furnace• temperature ~ 1350°C• charge: Pb source (ore, Pb scrap), Fe scrap, calcite, Si source• fuel (coal, coke)
Slag melt cooling
• 150-kg cone-shaped pots• gravity separation during cooling
0.85-3.0 wt.% PbO0.26-8.2 wt.% ZnO
up to hundreds ppmAs, Sb, Cu, Sn
slag
matte
metallic residue
Tsumeb smelting site (Namibia)
Tsumeb smelter (2007)
• ore mining/processing since 1907 (2 Mt Pb, 1 Mt Cu, 0.5 Mt Zn)• 200 kt slags on the dumps
Ettler et al. (2009): Appl. Geochem. 24, 1.Ettler et al. (2010): Comm. Geol. Survey Namibia 14, 3.
Nkana smelter (Kitwe, Zambia)• in operation 1930-2009
Nkana old slag dumps
• 20 Mt of Cu slag • 1.8 wt.% Cu, 2.4 wt.% Co• crushing to 15 mm• reprocessing and Co recovery
Chambishi smelter(Zambia)• electric arc furnace • Co recovery (alloy 14% Co) • 60-t glassy slag pots• evacuated to dumps
<<< Pb slag dumps
Slag exposure to weathering>>>
Příbram, Czech Republic
slag is milled and reused as a cover layer on mine tailing disposal site
Tsumeb, Namibia
Fine slag particle wind dispersal
• slag crushers• fine-grained slag particle dispersion in the environment (soils)
Kříbek et al. (2010): J. Geochem. Explor. 104, 69.
20 μm
Slag mineralogy - solid speciation
Ettler et al. (2001): Can. Mineral. 39, 873.Ettler et al. (2009): Appl. Geochem. 24, 1.
Vítková, Ettler et al. (2010): Mineral. Mag 74, 581.
Zn, Cu, Co enter into the structures of silicates, oxides and glassPb enters into the glass
Mel
Spl
Ol+Glass
Alteration products
Vítková, Ettler et al. (2010): Mineral. Mag. 74, 581.
Leaching experiments
• identification of dissolution and attenuation processes • long-term simulations of waste/water interactions• coupled to thermodynamic speciation-solubility modelling• coupled to investigation of newly-formed phases
• paralel extractions at different pH values• metal/metalloid leachability under various disposal scenarios (dumping, stabilization, reuse)
pH-static leaching test
Leaching behaviour
Vítková, Ettler et al. (2011): J. Hazard. Mater. 197, 417.
• not hazardous material according to EU limits• potentially high release of Cu and Co in acidic environments• dissolution of slag particles in soils (pH 4-5)
Conclusions #1Environmental stability of slags
• understanding of metal-/metalloid-hosting phases in slags is essential for subsequent determination of possible environmental impacts
• natural alteration products are indicators of long- term weathering processes
• leaching experiments – accelerated weathering >>> understanding and prediction of the chemical processes