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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
BRGM Orléans, FranceZdenek Johan, Patrice Piantone,…
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
Ongopolo Mines – Tsumeb smelter (Namibia)Hans Nolte
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.
• high-temperature Ca-Fe alumosilicates• spinel-family oxides• silicate glass• metallic fraction
melt enriched in metals(18 wt.% Pb, 12 wt.% Zn, 12 wt.% Cu, 8 wt.% As)
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
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
20 µm
20 µm
20 μm
• XRD – SEM – TEM• leached samples• geochemical modelling• natural weathering
cerussitePbCO3
cerussitePbCO3
HFO
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 Cu3Pb(AsO4)2(OH)2
• olivenite Cu2AsO4OH• lammerite Cu3(AsO4)2
• lavendulan NaCaCu5(AsO4)4Cl·5H2O• hydrocerussite Pb3(CO3)2(OH)• litharge PbO
Ettler et al. (2009): Appl. Geochem. 24, 1.
pH-static leaching experiments
• 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
• slag crushing and milling facilities generate highly reactive fine-grained dust
• high metal and metalloid release (mainly under low pH 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-derivedcontamination
in the environment
Soils in the vicinity of smelters are highlypolluted 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
FOREST SOIL(700 m of the smelter)
mobile Pb
• SEP and Pb isotopes: about 50% of Pb is very mobile• calculated vertical Pb migration velocity 0.3-0.36 cm/year
Pb concentration (mg/kg)
Dep
th (
cm)
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
pH-stat• pH-dependent release
• relevant for soil systems
Ettler et al. (2008) ES&T 42, 7878.Vítková et al. (2009) J. Hazard. Mater. 167, 427.
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% WHCpore 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 51x increase 250x increase 46x
• for a given pH range mostly independent Cd release
Soils and lead (Pb) distribution
increase 3x increase 16x
increase 1.4x
• strong pH-dependent release of Pb for given conditions
Chemical fractionation of metals
• shift towards more mobile forms after the fly ash exposure
Conclusions #2Fate 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 pH 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
