environmental impact of ore smelting: the african & european experience vojtěch ettler egg –...

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

Thanks for your attention!

ettler@natur.cuni.cz