- Количество слайдов: 42
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
Number of colleagues and students: Charles University in Prague Martin Mihaljevič, Ondřej Šebek, Ladislav Strnad, Jan Jehlička, Martina Vítková & many students BRGM Orléans, France Zdenek Johan, Patrice Piantone, … Université d´Orléans, France Jean-Claude Touray, Patrick Baillif, … Czech Geological Survey Bohdan Kříbek, František Veselovský, Vladimír Majer People from Zambian & Namibian universities / geological surveys: B. Mapani, F. Kamona, I. Nyambe, G. Schneider, …
Number of companies: Kovohutě Příbram CZ (Pb smelter) Zdeněk Kunický, Karel Vurm Ongopolo Mines – Tsumeb smelter (Namibia) Hans Nolte Chambishi and Mufulira smelters (Zambia) Tony Gonzáles and technical staff 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“)
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
Reducing fusion in shaft furnace • temperature ~ 1350°C • charge: Pb source (ore, Pb scrap), Fe scrap, calcite, Si source • fuel (coal, coke) Slag melt tipped off >>>
Slag melt cooling 0. 85 -3. 0 wt. % Pb. O 0. 26 -8. 2 wt. % Zn. O up to hundreds ppm As, Sb, Cu, Sn slag • 150 -kg cone-shaped pots • gravity separation during cooling 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 • 20 Mt of Cu slag • 1. 8 wt. % Cu, 2. 4 wt. % Co • crushing to 15 mm • reprocessing and Co recovery Nkana old slag dumps
Chambishi smelter (Zambia) • electric arc furnace • Co recovery (alloy 14% Co) • 60 -t glassy slag pots • evacuated to dumps
<<< Pb slag dumps Příbram, Czech Republic Slag exposure to weathering >>>
Tsumeb, Namibia slag is milled and reused as a cover layer on mine tailing disposal site
Fine slag particle wind dispersal 20 μm • slag crushers • fine-grained slag particle dispersion in the environment (soils) Kříbek et al. (2010): J. Geochem. Explor. 104, 69.
Slag mineralogy - solid speciation • high-temperature Ca-Fe alumosilicates • spinel-family oxides • silicate glass • metallic fraction Ol+Glass Mel melt enriched in metals (18 wt. % Pb, 12 wt. % Zn, 12 wt. % Cu, 8 wt. % As) Spl Zn, Cu, Co enter into the structures of silicates, oxides and glass Pb enters into the glass 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.
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 batch test liquid-to-solid (L/S) ratio
Pb slag - long-term Pb leaching (batch) Ettler et al. (2003): Mineral. Mag. 67, 1269.
Mineralogical controls cerussite Pb. CO 3 20 µm cerussite Pb. CO 3 • XRD – SEM – TEM • leached samples • geochemical modelling • natural weathering HFO 20 μm Ettler et al. (2003): Mineral. Mag. 67, 1269.
Pb slag - long-term Zn leaching (batch) Ettler et al. (2003): Mineral. Mag. 67, 1269.
Tsumeb slag – batch leaching Ettler et al. (2009): Appl. Geochem. 24, 1.
Natural alteration products • bayldonite Cu 3 Pb(As. O 4)2(OH)2 • olivenite Cu 2 As. O 4 OH • lammerite Cu 3(As. O 4)2 • lavendulan Na. Cu 5(As. O 4)4 Cl· 5 H 2 O • hydrocerussite Pb 3(CO 3)2(OH) • litharge Pb. O Ettler et al. (2009): Appl. Geochem. 24, 1.
p. H-static leaching experiments p. H-static leaching test • paralel extractions at different p. H values • metal/metalloid leachability under various disposal scenarios (dumping, stabilization, reuse)
Leaching behaviour • not hazardous material according to EU limits • potentially high release of Cu and Co in acidic environments • dissolution of slag particles in soils (p. H 4 -5) Vítková, Ettler et al. (2011): J. Hazard. Mater. 197, 417.
Conclusions #1 Environmental 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 longterm weathering processes • leaching experiments – accelerated weathering >>> understanding and prediction of the chemical processes
• slag crushing and milling facilities generate highly reactive fine-grained dust • high metal and metalloid release (mainly under low p. H conditions) • formation of secondary alteration products can lead to attenuation of contaminants • highly soluble weathering products can be dissolved during thunderstorm rain events
Fate of smelter-derived contamination in the environment Soils in the vicinity of smelters are highly polluted with metals/metalloids originating from smelter stack emissions (fly ash).
• Pb emissions from the Příbram smelter, CZ 1969: 624 t Pb y-1 1999: 1. 2 t Pb y-1
Pb migration in soil profiles Depth (cm) mobile Pb FOREST SOIL (700 m of the smelter) Pb concentration (mg/kg) • SEP and Pb isotopes: about 50% of Pb is very mobile • calculated vertical Pb migration velocity 0. 3 -0. 36 cm/year Ettler et al. (2005): Chemosphere 58, 1449. , Ettler et al. (2004): ABC 378, 311.
Soil pollution in Copperbelt, Zambia • topsoils/subsurface • maximum values Cu 41900 ppm Co 606 ppm Pb 503 ppm Zn 450 ppm As 255 ppm Kříbek et al. (2010) J. Geochem. Explor. 104, 69 -86
Fly ash reactivity – leaching tests • fly ash sampled at bag-house filters in the smelter • rapid dissolution of primary phases • p. H-dependent release • relevant for soil systems Ettler et al. (2008) ES&T 42, 7878. Vítková et al. (2009) J. Hazard. Mater. 167, 427. p. H-stat
Incubation of fly ash in soils • 0. 5 g fly ash • sealed by welding • testing bags – polyamide fabric (NYTREL TI) • mesh size 1 μm • double bags
Laboratory pot experiments 60% WHC pore water sampling in time
Metal release into soil water • high and quick release of Cd into soil and soil water • lower release of Pb – efficient attenuation processes
In situ experiments • sampling of soil before experiment • testing bag insertion
Soils and cadmium (Cd) distribution increase 51 x increase 250 x increase 46 x • for a given p. H range mostly independent Cd release
Soils and lead (Pb) distribution increase 1. 4 x increase 3 x increase 16 x • strong p. H-dependent release of Pb for given conditions
Chemical fractionation of metals • shift towards more mobile forms after the fly ash exposure
Conclusions #2 Fate of smelter emissions in soils • laboratory and in situ experiments help to decipher the processes affecting fly ash reactivity in soils • direct comparisons with polluted soils • smelter emissions are often composed of soluble phases • low soil p. H is accelerating the dissolution and influences subsequent mobility of contaminants in soil profiles
General conclusions • smelter-affected environments are convenient natural laboratories for understanding the dynamics and fate of anthropogenic contaminants • multi-method approaches needed • knowledge of behaviour of smelter-derived contaminants can help to innovate smelting technologies to be more „environment-friendly“ • indications for possible ways for recycling of smelting waste products
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