Sustainable development and
the environment
Mobility and Bioavailability of metals
Exposure to environment
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Overall metal bioavailability studies must take in to consideration following
Metals can be dispersed in soil and sediment, dissolved in ground and surface water, suspended as
particles in surface water, and in pore fluid in sediment .
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Most adverse effects can result form bioaccumulation of metals by biota in surface water and by plants
and animals in terrestrial environments.
Bioavailability is a complex function of
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total concentration and speciation (physical-chemical forms) of metals,
Mineralogy of soil, rock air particles,
pH, redox potential, temperature, total organic content (both particulate and dissolved fractions),
suspended particulate content, as well as volume of water, water velocity, and duration of water availability,
particularly in arid and semi-arid environments.
In addition, wind transport and removal from the atmosphere by rainfall
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In addition, metals can be dispersed into the atmosphere, by natural geochemical cycling and by other anthropogenic
processes (such as smelting and burning leaded gasoline and coal) and by microbial activities;
(frequency is more important than amount)
Many of these factors vary seasonally and temporally, and most factors are interrelated.
Consequently, changing one factor may affect several others.
Poorly understood biological factors seem to strongly influence bioaccumulation of metals and severely
inhibit prediction of metal bioavailability
Geochemical exploration data
• Geochemical exploration searches for anomalies in the
concentrations of chemical substances in a region.
• In site-specific investigations, geochemistry is a routine
procedure (in cold-temperate regions)
• the sampling density varies from a couple of meters to
several hundred.
• In glaciated areas the most common sample material is till,
– Contains ground bedrock material
– indirectly reflects the composition of bedrock.
• In addition to the sampling of soil (till,) a percussion drill may
be used to collect samples of drilling mud and crushed rock
from the bedrock surface.
Selective/sequential leaching
• Geochemical exploration uses as a routine so called selective
leaching techniques
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Aqua regia: pseudo total analysis (not most resistant minerals)
Nitric acid (or other strong acid): most silicates and all ore minerals
Ammonium oxalate: iron hydroxides
Weak (organic) acids: clay minerals, absorbed metals,
exchangeable cations, calcite
– Diluted salt; Water: soluble minerals salts, sulfates
• Extremely useful data for environmental assessments
– Speciation of metals
– Background and base line
– Exposure and risk analysis
• Mandatory for design of post-operational activities at sulfideore mines
– Treatment of tailings/remediation of soil contamination
Example: metal mining wastes with
arsenic
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Speciation of Fe and S in tailings
Solubility (sulphates)
Oxyhydroxides
– solubility varies with redoxconditions
– Desorption of metals (e.g. As)
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Distinction of requires
sequential/selective leaching
tests besides other analyses
Negligence of mineralogical
studies has lead to “remediation
and closure measures” that have
just worsened the situation
(mobilized As)
Environmental information from
sequential leaching
– Aqua regia: pseudo-total analysis (dissolves almost all, but not
all minerals): considered to provide conservative estimates of
metal pollution
• Does not differentiate mobile or stable speciation
– Ammonium oxalate: provides the contents of metals that can be
released if oxidized conditions change reduced
– Weak (organic) acids: estimates of bioavailable concentrations
in soils
– Water: soluble minerals salts, sulfates
Karabash – soil analysis
Metal contents in some tailings
and processing wastes are close
to economic ore deposits!
Using modern methods to
mineralogical reprocessing of the
mining tailings and wastes could
be used to reduce the pollution
• Soil sample mineralogy was analysed using XRD, and their chemistry by
selective leaching. (blue=bound by adsorption or soluble sulfates,
orange=bound by iron(III)hydroxides, yellow=bound by sulphides)
Exposure analysis and dose
assessment
Input to risk based
action planning:
– Distinguishes the
chemicals of
concerns
– Sets priorities to
remediation work
– Reflects the present
knowledge on health
risks
Geochemical modelling
Physical data
Hydrological data
Areal extent
Volume of
waste rock
Mean annual
temperature
Porosity
3.49e+6 m2
8.99e+7 m3
Precipitation
Evaporationx
+10 oC
Bulk density
1695 kg
/m3
Water flow
rates
-to Kazretula
river
-to Poladauri
riverx
- discharge to
groundwaterx
39 %
700 mm /y
50 %
300 m3 /d
Mineralogical
composition vol-% #
quartz
78
sericite
7
Drainage water
chemistry in mg/L *
pH
2.65
SO4214794
pyrite
3.1
Fetot
1630
chalcopyrite
0.8
Cu2+
1100
AMD in Bolnisi Mining Area,
Georgia
Solute flows to Kazretula River
50 m3 /d
sphalerite
0.1
Zn2+
682
3000 m3 /d
chlorite
11
Mg2+
1100
Mol /s
Tonnes /y
Solute flows to the streams entering
the Poladauri River
Mol /s
Tonnes /y
SO4
0.532
1620
SO42-
0.089
270
SO42-
5.315
16200
Fetot
0.101
178
Fetot
0.017
30
Fetot
1.013
1784
120
2+
20
2+
0.601
1204
2+
0.362
746
1.571
1204
2-
Cu
Zn
2+
0.060
2+
0.036
2+
Mg
0.157
Cu
75
Zn
2+
120
Mg
Mineral contents
Mol
2+
0.010
0.006
Cu
13
0.026
Zn
2+
20
Mg
Mineral weathering rates
kg
Solute flows infiltrating to the
groundwater
Mol /s
Tonnes /y
Mineral lifetimes
Mol /s
Years
pyrite
3.94e +10
4.72e +9
pyrite
2.095
pyrite
596
chalcopyrite
6.64e +9
1.22e +9
chalcopyrite
0.671
chalcopyrite
314
sphalerite
1.56e +9
1.52e +8
sphalerite
0.404
sphalerite
123
chlorite
3.02e +10
1.68e +10
chlorite
0.351
chlorite
2724
Bolnisi-mining area
georgiamodel0905_Heads
689.842113
670.564793
651.287472
632.0101509
Irrigation
channels
612.73283
593.455509
574.178188
554.900867
Contaminated
streams from
tailings
Y
Z
X
Contaminated
river
Scope modelling
new species
0.99
0.92
0.85
0.78
0.71
0.64
0.57
0.5
0.43
0.36
0.29
0.22
0.15
0.08
0.01
new species
0.985
0.915
0.845
0.775
0.705
0.635
0.565
0.495
0.425
0.355
0.285
0.215
0.145
0.075
0.005
Y
Y
Z
X
Z
X
Toxic metals
• Subjects of particular concern include various metals,
– chromium, nickel, copper, manganese, mercury, cadmium, and
lead, (not forgetting uranium, thorium, radium)
• and metalloids, including
– arsenic, antimony, and selenium
• Near former mine sites, dumps, tailing piles, and
impoundments,
• In urban areas and industrial centers
• Higher than average abundances of these elements in soil,
sediment, water, and organic materials,
• In some cases due to past mining and (or) industrial activity,
may cause the formation of the more bioavailable forms of
toxic heavy metals.
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Bioavailability is a complex function of
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In addition, to aqueous transport, wind transport
and removal from the atmosphere by rainfall
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total concentration and speciation (physicalchemical forms) of metals,
Mineralogy of soil, rock air particles,
pH, redox potential, temperature, total organic
content (both particulate and dissolved fractions),
suspended particulate content, as well as volume
of water, water velocity, and duration of water
availability, particularly in arid and semi-arid
environments.
(frequency is more important than amount)
Many of these factors vary seasonally and
temporally, and most factors are interrelated.
Consequently, changing one factor may affect
several others.
Poorly understood biological factors seem to
strongly influence bioaccumulation of metals and
severely inhibit prediction of metal bioavailability
Isotopes as tools to assess exposure
Toxicity of Zn depends substantially on the hardness of
water!!
Partitioning of metals in surface waters
and sediments
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After discharge to an aquatic environment but before uptake by organisms, metals are partitioned between solid and
liquid phases.
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Within each phase, further partitioning occurs
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determined by ligand concentrations and metal-ligand bond strengths.
In solid phases, soil, sediment, and surface water particulates, metals may be partitioned into six fractions:
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(a) dissolved,
(b) exchangeable,
(c) carbonate,
(d) iron-manganese oxide,
(e) organic,
(f) crystalline
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Various metals partition differently among these fractions
Partitioning is affected strongly by variations in pH, redox state, organic content, and other environmental factors
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The relative mobility and bioavailability of trace metals associated with different fractions are shown in the next slide
The dissolved fraction consists of
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carbonate complexes, whose abundance increases with pH,
metals in solution, including metal cation and anion complexes and hydrated ions
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whose solubilities are affected strongly by pH and tend to increase with decreasing pH
Metal mobility and bioavailability
Metal species and association
Mobility
Exchangeable (dissolved) cations
High.Changes in major cationic composition may
cause a release due to ion exchange (estuarines,
mixing of saline groundwater with surface water)
Metals associated with Fe-Mn oxides
Medium. Changes in redox conditions may cause
a release but some metals precipitate if sulfide
mineral present is insoluble
Metals associated with organic matter
Medium/High Decomposition/oxidation of organic
matter occurs in time
Metals associated with sulfide minerals
Strongly dependent on environmental conditions.
Under oxygen-rich conditions, oxidation of sulfide
minerals leads to release of metals.
Metals fixed in crystalline phase
Low. Only available after weathering or
decomposition
Spread of metals in surface water
• In mining areas soils have commonly high
concentrations of metals
• Sediments in streams and lakes in the catchments areas
of mineral deposits provide information about
– Transport and distribution and partitioning of metals in
sediments
• Eg. Some of the springs existing in Talvivaara catchment area
where discharging acid drainages (pH 3.5!) before the mine was
build providing (with black shales present in the region) “an natural
analog” for the mine pollution spread (of Ni and U)
Particle size effects and “mineral
liberation factor”
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Particulate size and resulting total surface area available for adsorption
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Small particles with large surface-area-to-mass ratios allow more adsorption
than an equivalent mass of large particles with small surface-area-to-mass
ratios.
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Reduced adsorption can increase metal bioavailability by increasing concentrations of
dissolved metals in associated water.
The size of particles released during mining depends on mining and
beneficiation methods. Finely milled ore may release much smaller particles
that can
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important factors in adsorption processes
affect metal bioavailability
both be more widely dispersed by water and wind,
serve as sites of enhanced adsorption.
Consequently, mine tailings released into fine-grained sediment such as silty
clays found in many playas can have much lower environmental impact than
those released into sand or coarse-grained sediment with lower surface area
and adsorption.
(Natural attenuation by sorption)
Sulfide Oxidation
(1)
FeS2 + 7/2 O2 + H2O  Fe2+ + 2 SO42- + 2 H+
Fe1-xS + (2-x/2) O2 + x H2O  (1-x) Fe2+ + SO42- + 2x H+ (2)
Fe2+ + 1/4 O2 + 5/2 H2O Fe(OH)3 + 2 H+
Complete oxidation of pyrite:
FeS2 + 15/4 O2 + 7/2H2O  Fe2+ + 2 SO42- + 4 H+
If oxygen is limited (maximum solubility to groundwater) incomplete
oxidation can take place according to (1)
If pH is > 3.5, Fe(OH)3 will precipitate
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Iron crust can stop neutralization by carbonates
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iron-oxy-hydroxides can absorb metal (and they stay there as long as
Fe(OH)3 (or other Fe-oxy-hydroxides) are stable: changes in conditions can
release them.
If however, pH is low (< 5) and oxygen is present the much more acid
generating reactions with FeIII can take place !
• In stead of ferric hydroxide
(metastable) more complex
reactions of ferric oxyhydroxides and hydroxysulfates
can take place
Secondary Minerals
Ferric hydroxides & hydroxysulfates
 Schwertmannite
Fe8O8 (SO4)(OH)6
 Jarosite KFe3 (SO4)2(OH)6
 Ferrihydrite Fe5OH8•4H2O
 Goethite a-FeO(OH)
Oxidation with Ferric Iron
FeS2 + 14 Fe3+ + 8 H2O 
15 Fe2+ + 2 SO42- + 16 H+
Fe1-xS + (8-2x) Fe3+ + 4 H2O 
(9-3x) Fe2+ + SO42- + 8 H+
Fe2+ + ¼ O2 + H+  Fe3+ + ½ H2O
These reactions are commonly cathalysed by microbes!
Acid generating and secondary
minerals producing reactions
Sorption of metals on hydrated ferric
oxides
Representative curves on
sorption of metals on ferrous
oxy-hydroxides
Modelled for 1g/L of ferric
oxide-sorbent
Representative curves on
sorption of oxyanions on
ferrous oxy-hydroxides.
Modelled for 1g/L of ferric
oxide-sorbent
Compositional fractioning
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Adsorption is pH-dependent taking place (only) in a certain range of pH
The adsorption edge, the pH range over which the rapid change in
sorption capacity occurs, varies among metals,
– precipitation of different metals over a large range of pH units.
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mixing metal-rich + acidic water with higher pH+ metal-poor water
results in fractionation and separation of metals as different metals are
adsorbed onto various media over a range of pH values.
Cadmium and zinc tend to have adsorption edges at higher pH than
iron and copper, and consequently they are likely to be more mobile
and more widely dispersed.
Adsorption edges also vary with concentration of the complexing agent;
thus, increasing concentrations of complexing agent increases pH of
the adsorption edge
Major cations such as Mg+2 and Ca+2 also compete for adsorption
sites with metals and can reduce the amount of metal adsorption
Metals in sulphides
• In reducing aquatic environments metals from mining
activities are commonly associated with sulfide minerals
• Either primary (in the ore deposit) or formed by bacterial
reduction of the (secondary) sulfates in oxidized tailings.
– These reactions are applied in remediation!
• Most metal sulfide minerals are quite immobile, as long
as they remain in a chemically reducing environment,
– may have little impact on biota despite of anomalous metal
concentrations
Oxidation with Dissolved O2
ZnS + 2 O2  Zn2+ + SO42PbS + 2 O2  PbSO4
Oxidation with Ferric Iron
ZnS + 8 Fe3+ + 4 H2O 
Zn2+ + 8 Fe2+ + SO42- + 8 H+
• In recent organic carbon-rich sediments, trapped interstitial
fluids can commonly form a strongly reducing (anoxic)
environment. Low redox potential in this environment can
promote sulfate reduction and sulfide mineral deposition.
– Much of the non-silicate-bound fraction of potentially toxic metals
such as arsenic, cadmium, copper, mercury, lead, and zinc, can be
co-precipitated with pyrite, form insoluble sulfides, and become
unavailable to biota
– Seasonal variation in flow rates or storms, floods that induce an
influx of oxygenated water can result in rapid reaction of this anoxic
sediment and thereby release significant proportions of these
metals.
• Also co-precipitation of As in oxic environments can be used
to bound it efficiently to non-bioavailable form (Ca-Fearsenate with Ca/Fe about 1/6)
Metal uptake by plants
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Plant species and relative abundance and availability of necessary elements
also control metal uptake rates.
Abundant bioavailable amounts of essential nutrients, including phosphorous
and calcium, can decrease plant uptake of non-essential but chemically similar
elements, including arsenic and cadmium, respectively.
More complex interactions are also observed: bioavailability may be related to
multi-element amounts or ratios. For example, copper toxicity is related to low
abundances of zinc, iron, molybdenum and (or) sulfate).
Widely studied in agricultural sciences
In the scientific literature, many studies describe anthropogenic (industrial or
mining) contributions to elemental abundances, and their bioavailability
controls, in the environment. E.g.
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occurrence of heavy metals in soil near and far from urban pollution;
formation of acid mine drainage; uptake of heavy metals by plants in lab experiments and
uptake of metals by vertebrates in the vicinity of zinc smelters
Arsenic in groundwater e.g. Finland, public health impacts of arsenic groundwater Hungary
Metal up take into aquatic organism
• Metal uptake by plants and partitioning in the soil are combined in
the aquatic environment.
• Two major pathways (uptake vectors) are available for metal
incorporation in deposit- and (or) 13 detritus-feeding aquatic
species:
• (1) ingestion of metal-enriched sediment and suspended particles
during feeding, and
• (2) uptake from solution
• Consequently, knowledge of geochemical reactions of metals in
both water and sediment is necessary to understand controls on
metal bioavailability in natural water.
• Many biological factors controlling metal bioaccumulation in a
aquatic organisms are not understood; this fact severely limits our
understanding of metal bioavailability
– Regulations can be expected to change
Acid Neutralization
CaCO3 + H+  Ca2+ + HCO32KAlSi3O8 + H+ + 7 H2O 
K+ + 3H4SiO4 + Al(OH)3
CaAl2Si2O8 + 2 H+ + H2O 
Ca2+ + Al2Si2O5(OH)4
Acid-Base Accounting
FeS2 + 2CaCO3 + 3.75O2 + 1.5H2O = Fe(OH)3 +
2SO42- + Ca2+ + CO2
AP: Acid-producing potential
NP: Acid-neutralizing potential
NNP: Net neutralizing potential
NNP = NP - AP
Secondary Minerals
Sulfates
 Highly
soluble
 Melanterite FeIISO4•7H2O
 Rozenite FeIISO4•4H2O
 Copiapite
FeIIFeIII4(SO4)6(OH)2•20H2O
 Halotrichite FeIIAl2(SO4)4•22H2O
 Goslarite ZnSO4•7H2O
 Moderately
 Gypsum
soluble
CaSO4•2H2O
Contrary
Creek,
Virginia
Climatic conditions effect
the solubility of secondary
minerals, particlularly
Vermont: peaks after
spring discharge
Virginia peaks during hot
summers
Secondary Minerals
Aluminum hydroxides &
hydroxysulfates
 Amorphous Al(OH)3
g-Al(OH)3
 Jurbanite Al(SO4)(OH)6•5H2O
 Basaluminite Al4 (SO4)(OH)10•5H2O
 Gibbsite
Secondary Minerals
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Metal-sulfate salts
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Highly soluble
Store acidity and metals
Cycle metals via evaporation and
dissolution
Ferric hydroxides
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pH-dependent sorption of metals
Classification of Seafloor
Massive Sulfide Deposits
Volcanic
Sediments>
Assemblage Volcanics
Volcanics=
Sediments
Volcanics>
Sediments
Bimodal
Felsic>Mafic
Bathurst
Kuroko
Bimodal
Sedimentary- Besshi
Mafic>Felsic Exhalative
Noranda
Mafic and
Ultramafic
Cyprus
Uses of Models
Mitigation and planning at future mines
 Remediation at abandoned mines
 Land-use planning
