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



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)



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



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



Lava Cap Mine Superfund Site, Nevada Cty, CA



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



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



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



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)



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)



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



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



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



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



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



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



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



Lava Cap Mine Superfund Site, Nevada Cty, CA



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.



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.



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.



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



Ultra-high As gold mines in Nova Scotia, Canada

Walker et al (2009) Canadian Mineralogist v 47



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



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)



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)



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



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



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



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)



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



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



As Speciation in Pteris vittata Hyperaccumulating

Fern

Webb et al (2003) ES&T

Pickering et al. Environ. Sci. Technol., 40 (2006) 5010-5014.



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



The End

Leptothrix ochracea from the Lava Cap Mine

Arsenic Exposure

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