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Transcript of Arsenic Exposure
7/29/2019 Arsenic Exposure
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Identification and Quantification of
Arsenic Species in Gold Mine WastesUsing Synchrotron-Based X-rayTechniques
Andrea L. Foster, PhD
U.S. Geological Survey GMEGMenlo Park, CA
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Arsenic is an element of concern in mined gold
deposits around the world
Don PedroHarvard/Jamestown
Kelly/Rand (Au/Ag)
Ruth Mine (Cu)
Spenceville (Cu-Au-Ag)Lava Cap (Nevada)
Empire Mine (Nevada) low-sulfide, qtz AuArgonaut Mine (Au)
Ketza River (Au)sulfide and oxide or
ebodies
Goldenville, Caribou,and Montague (Au)
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The common arsenic-rich particles in hard-rock gold mineshave long been known
Arsenopyrite FeAsS
PrimarySecondary
Scorodite FeAsO4 2H2OKankite : FeAsO4•3.5H2O
Jarosite KFe3(SO4)2(OH)6
Tooleite [Fe6(AsO3)4(SO4)(OH)4•4H2OPharmacosiderite KFe4(AsO4)3(OH)4•6–7H2O
Secondary/Tertiary
Iron oxyhydroxide (“rust”)containing arsenic up to 20 wt%
arsenide
n = 1-3
n-
Arseniosiderite Ca2Fe3(AsO4)3O2·3H2OYukonite Ca7Fe12(AsO4)10(OH)20•15H2O
“arsenian” pyriteAs-1 pyrite Fe(As,S)2
Reich and Becker (2006):maximum of 6% As-1
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But it is still difficult to predict with an acceptable
degree of uncertainty which forms will be present
• thermodynamic data lacking or
unreliable for many important phases
• kinetic barriers to equilibrium
• changing geochemical conditions
(tailings management)
Langmuir et al. (2006) GCA v70
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Lava Cap Mine Superfund Site, Nevada Cty, CA
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Typical exposure pathways at arsenic-contaminated sites are
linked to particles and their dissolution in aqueous fluids
ingestion of arsenic-bearing water
solid-phase arsenicnear-neutral, low dissolved organic carbon,low salinity waters
inhalation or ingestion of arsenic-rich particles
solid-phase arsenic
lung and gastic/intestinal tract fluids (saline,
aqueous solutions-high dissolved organiccarbon, enzymes, bile, some low pH, mostnear-neutral)
• critical to know the form(s) of arsenic in the solid phase
• only a subset of those forms may be reactive
dissolution
dissolution
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This talk will review the results of synchrotronX-ray studies of arsenic speciation, with focus on gold mine wastes
Brilliant, high flux radiation produced at points
tangent to
a circular orbit of electrons moving at near-
relativistic speeds
75 synchrotrons around the world
10 in US (4 suitable for environmental work)
Stanford
Berkeley
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Large ( 1-10 mm) or small (2 -150 μm) X-ray beams are
available for most techniquesBulk
Microbeam Precision stage
(micron)
CCD detector
(diffraction)
Solid-state
detector
Gas ionization
detector
• X-ray Fluorescence• X-ray AbsorptionSpectroscopy• X-ray Diffraction
X-ray PhotoelectronSpectroscopy• Vibrational Spectroscopies• Magnetic spectroscopy• Small Angle ScatteringCCD Detector
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Synchrotron X-ray Fluorescence (XRF) Spectrometry
Bulk Microbeam
One EDS spectrumPer point (> 1000)
Elemental IDElement CorrelationSpatial distribution
As
Ca
Fe
1800 microns
Elemental ID
One average Spectrum
CaFe As
Voltage (energy)
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Synchrotron-based X-ray Diffraction (SXRD)
2-D pattern
goethite/lepidocrocitemixture
Synchrotron XRD20 min
1-D patterns
Conventional XRD8 hours
• Mineral ID• Mineral Mapping
• Amorphous materials(scattering)
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X-ray Absorption Fine Structure Spectroscopy
X-ray Absorption NearEdge Structure (XANES)Oxidation state, species “fingerprinting”
A
b s o r b a n c e
Energy (eV)
> 1 mg/kg
E X A F S f u n c t i o n χ ( k )
Photoelectron Wave vector k (Å-1)
Extended X-ray Absorption Fine Structure (EXAFS)Speciation = identity, #, distance of neighboring atoms
> 75 mg/kg
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Spectral Deconvolution by Least-Squares Fits
Orpiment (As3+-S)
As5+ on rust (iron oxyhydroxide)
As3+
in water (As3+
-O)
13.5 % As5+
86.5% As3+
Bangladesh Aquifer Sediment
10-10.4 meters depth
As3+
As5+
Unique spectral shape
Energy increases with
oxidation state
Arsenopyrite (As1-)
Energy, (electron volts)11860 11880 11900 11920
XANES spectra
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Principal Component Analysis of XANES or EXAFS
Spectra
Energy (eV)
C o m
p o n e n t I n t e n s i t y
1
2
3
4
5
6
7
n
Energy
Set of Unknown XANES Spectra
PCA
Principal Components
(= number of species)
Subset “best” model compounds
For LSA
P C 2 ( v 2
* w 2 , i )
2 2 % o
f v a r i a n c e
PC 1 (v1*w1,i)35% of variance
Variance Plot
N = 19
Energy (eV)
Set of Model Compound XANES Spectra
TargetTransformationUsing principalcomponents N = 30
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Synchrotron studies of As in Gold Mine WastesEarly Days: 1994-2002
individual field and lab projects at “targets of
opportunity, typically with limited connection
to regulators’ needs
Bulk XANES + EXAFS
2003- present
collaborative projects at high-profile
sites; research focused on
addressing needs
Microbeam studies: 2005 and later
Coupled XAFS, XRD XRF
Coupled bulk and microbeam
Multi-metal XAFS
Complimentary Lab-based
techniques
Micro Raman, XRD
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As Lα50 μm
Fe K α
3 4 5 6 7 8 9 10 11 12
k (Å-1)
0 1 2 3 4 5 6
Radial Distance (Å
datafit
As(V)-Gibbsite
As(V)-FeOOH
RM
a b As-O
As-Al/Fe
As-Fe
As-Al
Energy (eV)11850 1195011900
As5+
As-Fe = 3.25 Å
FeFe
As
As
AlAl
As-Al 3.16 Å
Ruth Mine: Ballarat District (Trona, CA)
Tailings (ca 1000 mg/kg As) used for residential
landscaping
Foster et al., (1998) American Mineralogist 83, 553-568
D
. L a w l e r , B L M
Ruth MineTrona, CA
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Mesa De Oro: Should be “Mesa de Arsenico”
http://www.pbs.org/newshour/bb/environment/superfund_4-16.html (transcript of 1996 show
called “Paying for the Past”)
• Gold tailings with 115 – 1320 mg/kg arsenic• 40 homes developed on Mesa between1975-1985• EPA emergency response
• halted new home construction• removed and replaced about 1 foot of soil• shored up sides of Mesa
George Wheeldon,“geologist”: arsenic fromthe mine is in a form thatis not dangerous
Time Magazine Sept 25, 2000
San Jose Mercury News
Residents won 2,000,000 for loss of property valuehttp://consumerlawpage.com/article/environmental_pollution_1.shtml
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XANES spectra of Mesa de Oro soil samplesdemonstrate that arsenic is not in arsenopyrite form
Arsenopyrite FeAsSAs5+ on rust (iron oxyhydroxide)
Arsenopyrite (As1-)
Energy (KeV)
11.86 11.88 11.90 11.92
Arsenic (V) on Rust
Range of Mesa de OroSamples (n =4)
Mr Wheeldon’s Error: assuming that arsenic
stays in original form A. Foster, R. Ashley, and J. Rytuba, USGS: unpublished data
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Lava Cap Mine Superfund Site, Nevada Cty, CA
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Arsenic species in mine-impacted sediment from
the Lava Cap Mine
Foster et al., (2010) Geochemical Transactions
pyrite arsenopyrite
pronounced
oxidation
minimal
oxidation
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0
P C 2 ( v
2 * w 2 , i )
2 2 % o f v a r i a n c e
PC 1 (v1*w1,i)35% of variance
subareal tailings
≈ 30% FeAsS
Pyrite-rich ore69% Fe(As,S)2
≈ 65% FeAsS
Arsenopyrite-rich ore
(FeAsS)
submerged tailings
typical ore
2 4 6 8 10 12 14
subareal tailings
photoelectron wave vector k (Å-1)
k 3 - w e i g h t e d E X A F S
Our first studies at Lava Cap showed that submerged tailings from the private lake containAs in its original forms. Tailings exposed to air after the burst of a log dam in 1998 haveoxidized considerably.
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Kelly/Rand Mines: Ultra-high arsenic in mine tailings
• gold-silver mines operated until 1947• approximate volume: 100,000 tons• breach of tailings levee; migration of tailings intoresidences in Randsburg• 3000->10,000 mg/kg As
• remote, Federal Land (BLM), popular with OHVersKim, C.S., Wilson, K.M., and Rytuba, J.J. (2011) Particle-size dependence on metal
distributions in mine wastes: implications for water contamination and human
exposure. Applied Geochemistry 26, 484-495.
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Secondary arsenates and As5+-rich sulfate phasespredominate in Kelly/Rand tailings
0
20
40
60
80
100
120
“background”soil
FeAsO4 2H2O
am-FeAsO4
Ca2Fe3(AsO4)3O2 3H2O
KFe3[(S,As)O4)](OH)6
As-FeOOH
Secondary crustsTailingsLow-gradeOre
L i n e a
r C o m b i n a t i o n f i t s t o E X A F S
• no evidence for primary sulfide phases (below detection? Oxidized?)
• solubility and kinetics of dissolution of precipitates is expected to be verydifferent than that of arsenic on ferric oxyhydroxide
Kim, C.S., Wilson, K.M., and Rytuba, J.J. (2011) Particle-size dependence on metal
distributions in mine wastes: implications for water contamination and humanexposure. Applied Geochemistry 26, 484-495.
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Lungs of tortoises collected near mines contain
particles similar to those found in mine tailings
687 lung tissue
11860 11880 11900 11920
scorodite
jarosite
Spot 2
Spot 1
4.6 mm
3 . 5 m
mAs
12
A. Foster, unpublished data
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Ultra-high As gold mines in Nova Scotia, Canada
Walker et al (2009) Canadian Mineralogist v 47
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Current and Future directions in synchrotron-based
arsenic research
• Validated method for As bioaccessibility test
– Coupled to geochemistry, As speciation• Bioreactors (anaerobic and aerobic)
– Aerobic: naturally-occurring microbial consortia?
– Anaerobic: relative bioaccessibility of As in neo-sulfides vs. organic compounds (biomass)
• Plants
– Finding more accumulators, maximizing uptake – Coupling genetics, protein expression, and location of metal (As) sequestration
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Arsenic Relative Bioavailability Project (EmpireMine State Historic Park)
N =2525
ChemistryX-ray diffractionElectron ProbeQEMSCAN
Particle size analysis“Bulk” Synchrotronstudies “Microfocused”
Synchrotron studies
In vitro
In vivo
Model of mineralogical control
on As bioaccessibility
Correlation with easily-
measured parameter
Helping to find a cost-effective means of evaluating the potential forre-development of mined lands contaminated with arsenic
% Bioaccessible
% B
i o a v a i l a b l e
This study is conducted through a proposal by CA Department of Toxic Substances Control and USGS that was funded
by US-EPA (Brownfields Program)
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Principal Component Analysis predicts
4-5 unique arsenic species
-0.2
0.3
0.8
1.3
-0.2 0.3 0.8
-0.8
-0.4
0
0.4
0.8
-0.8 -0.4 0 0.4
Component 1
C
o m p o n e n t 2
Component 1
C o m p o n e n t 2
N =19
N =18
Outlier removed
Variance can be visualized on additional
Component axes (3, 4, 5)
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Bioaccessibility and Bioavailability have similar
trends with key arsenic species
% r e l a t i v e
b i o a v a i l a b i l i t y
R² = 0.3028
0
5
10
15
20
25
30
35
0.0% 10.0% 20.0% 30.0% 40.0%
Ca-Fe-Arsenate
bioday 6/7
bioday 9/10
bioday 12/13
bioall days
R² = 0.9484
0
5
10
15
20
25
30
35
0 0.1 0.2 0.3 0.4 0.5 0.6
Pyrite/Arsenopy
R² = 0.28
0.0
2.0
4.0
6.0
8.0
10.0
12.0
0.0% 5.0% 10.0% 15.0% 20.0% 25.0% 30.0% 35.0% 40.0%
Ca-Fe arsenate
R² = 0.385
0.0
2.0
4.0
6.0
8.0
10.0
12.0
0 0.1 0.2 0.3 0.4 0.5 0.6
As-Sulfides
Ca-Fe-Arsenate
Pyrite/Arsenopyrite
SEE MORE AT ALPERS TALK TOMORROW SESSION 10
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Arsenic in roasted ore treated by an anerobic
biochemical reactorMaghemite-richMore As3+
Hematite-richLess As3+
Paktunc et al. (2008) Proceedings of the 9th Intl Conference for Appl. Mineralogy
Anerobic Reactor SamplesMostly As3+, but organicNOT SULFIDE (??) As3+
SCH
3 CH3
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New and improved pyrite: now with
As3+ Deditius et al (2008)Yanacocha , Peru
Should be present in other low-sulfidation epithermal deposits:Nevada Au?
(Fe,Au)(As,S)2
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Arsenic attenuation by naturally-occurringmicrobial consortia: Lava Cap Mine (NPL), CA
0
5000
10000
15000
20000
25000
30000
A r s e n i c ( m g / k g )
LL1
LL10
LL1adj
LL2sed
LL2 Fe flocalgae
LL2
LL1LL1adj
LL10
Foster et al, USGS Open File Report 2009-1268
LL1LL10
LL2 algae
LL2 fe floc
LL1 adj
LL2 sediment
Biogenic Fe-(hydroxide) accumulatesarsenic to levels several times to ordersof magnitude greater than the originalmine tailngs (yellow horizontal line)
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Monitoring the performance of a
natural passive bioreactor
LL1LL10
0
10
20
30
40
50
60
70
8090
100
Jun 06 Oct 06 Nov 06 Feb 07 Mar 07 Aug 07 Oct 07 Mar 08
AsFeMn
As: 12-30 μg/l 10 μg/l
Mn: 235-2000 μg/l 300 μg/l
EPA cleanup goal:
% r e m o v e d b e t w e e n
L L 1
a n d L L 1 0
Concentration range at LL10
A i i i d i h F O h d id h h
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Arsenic is associated with Fe Oxyhydroxides rather thanwith biological materials (contrast the anerobic treatment
of Paktunc)
-0.10
0.16
0.11 0.46
99AF-wLL5
00AF-LCD1a
post-rinse
00AF-LCD1a
v 2
* w 2 , i
v1*w1,i
As(V)-FeOOH
dominant
1000x
EPA region 9 Superfund has a pilotaerobic /anerobic treatment in place atthe adit, but is not supplanting it with thenative microorganisms
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As Speciation in Pteris vittata Hyperaccumulating
Fern
Webb et al (2003) ES&T
Pickering et al. Environ. Sci. Technol., 40 (2006) 5010-5014.
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Synchrotron techniques have had great utility in the study of arsenic speciation in gold mines..there is more to come!
Arsenopyrite
Primary (ore,concentrates)
Pyrite
n = -1, +3
n
3+
5+
O
S
Fe
As-poor
acidic
Near-neutralCa minerals
FeOOH
Ca-Fe arsenates
As-rich
Fe arsenatesFe sulfates
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The End
Leptothrix ochracea from the Lava Cap Mine