Th O d SThe Occurrence and SThe Occurrence and S

Serpentinites in NoSerpentinites in NoSerpentinites in NoLijie NIU1 Keiko HATTORI1* YLijie NIU1, Keiko HATTORI1 , Yj , ,

1- Dept of Earth Sciences University of Ottawa Ottaw1 Dept. of Earth Sciences, University of Ottawa, Ottaw2- Dept of Earth and Planetary Systems Science HiroDept. of Earth and Planetary Systems Science, Hiro33- Dept of Geology Middlebury College Middlebury VDept. of Geology, Middlebury College, Middlebury, V

ABSTABSTHigh concentrations of As are reported in ground waters and bedrocks in many parts of New England (AHigh concentrations of As are reported in ground waters and bedrocks in many parts of New England (A

(up to 449 ppm in serpentinites and 1 100 ppm in talc magnesite rocks) in northern Vermont Altered u(up to 449 ppm in serpentinites and 1,100 ppm in talc-magnesite rocks) in northern Vermont. Altered ut ti ti it f th V t (103 450 A i b lk k ) Thi t d i l d trepresentative serpentinites from northern Vermont (103-450 ppm As in bulk rocks). This study includes t

mineral separates, as well as X-ray absorption fine structure (XAFS) study of As in the mineral separates.p y p ( ) y pexperiments, 20 to 30% of As is dissolved, suggesting that this fraction is probably adsorbed on antigorite. Itexperiments, 20 to 30% of As is dissolved, suggesting that this fraction is probably adsorbed on antigorite. ItK-edge showed that the As is predominantly As(III) in our serpentinite samples EXAFS spectra shows thaK-edge showed that the As is predominantly As(III) in our serpentinite samples. EXAFS spectra shows thapositive correlation between Fe and As abundances which can be explained by the charge compensation epositive correlation between Fe and As abundances, which can be explained by the charge compensation eHi l h th t A (V) i fi d i ti it b l i Si(IV) i ti it (H tt i t l 2005) ThHimalayas show that As (V) is fixed in serpentinites by replacing Si(IV) in antigorite (Hattori,et al. 2005). Thserpentine crystal structure, and the speciation of As in serpentinites is controlled by the oxidation state of Asse pe e c ys a s uc u e, a d e spec a o o s se pe es s co o ed by e o da o s a e o s

BACKGROUNDBACKGROUNDArsenic is well known for its potent toxicity and has caused health problems in many regions in the worlArsenic is well known for its potent toxicity and has caused health problems in many regions in the worl

as well as fruits and vegetables that are grown on As rich soil Ryan et al (2009) showed that ground water inas well as fruits and vegetables that are grown on As-rich soil. Ryan et al. (2009) showed that ground water in

phase of As, oxidation state of As, and local atomic structure of As in serpentinites in order to understand incop p

METMETSerpentinite samples were collected from the

Study Site: ~ 44.75 N and 72.5 W)Serpentinite samples were collected from the

th V t USA h A i hi h i d tnorthern Vermont, USA, where As is high in ground water.

Concentration of As reached as high as 300 ppb inConcentration of As reached as high as 300 ppb in

groundwater and over 1000 ppm in some rocksgroundwater, and over 1000 ppm in some rocks.

Ott CAN Vermont U S AOttawa, CAN. Vermont, U.S.A.

( Dolan,1996)

RESULTS dRESULTS andRESULTS andAntigorite

EPMA analysis shows that the c

g

EPMA analysis shows that the c

id b l th d t ti liXANESNo 2 oxides are below the detection li

(24 9)

No. 2

did not show a AsK! peak, where(24,9)

BH-4, XANESN 1

p ,(13,15)

BH 4,SpotB

No. 1

MagnetiteMagnetite

a. b.FeAs b.

A ti itAntigorite

(24 9)(24,9)

BH-4,

BH5 Grain E

SpotF Cr-spinel

BH-4: major antigorite (white)

BH5, Grain E

BH-4: major antigorite (white)

contain magnetite ( black)XANESNo 3contain magnetite ( black)

As(8,28) FeAs

No. 3

AsX41 X 40d.c.

X-ray fluorescence (XRF) images near the boundaries between antigorite andd

XX

3936Fe oxides of sample Large grains of Fe oxides have Cr-spinel cores rimmed

X

X 37

38

p g g p

by magnetite. Red color corresponds to higher concentration of elements. Theby magnetite. Red color corresponds to higher concentration of elements. The

locations for micro-XAFS with 5 "m beam are shown with open circles.locations for micro XAFS with 5 "m beam are shown with open circles.

The results show that antigorite has higher As concentration than Fe Left: Electron back scattered image of Cr-sThe results show that antigorite has higher As concentration than Fe

id EPMA l h hi h f A i ti it ( t 1300 )

g

within antigorite matrix (black).oxides. EPMA also shows high conc of As in antigorite (up to 1300 ppm). Right: K! peak of As on antigorite compare

As(III) on Fe(OH)3 AsO33-

BH-5BH-43

Table 1. Leaching experiment results. Two sources of As20

g p Two sources of As

leached by phosphate solution;Concentration (ppm)L hi leached by phosphate solution;

As adsorbed on antigorite andBH 4 BH 5

Concentration (ppm)Elements

Leaching

l i As adsorbed on antigorite and

A i t d i b tBH-4 BH-5solution

15As incorporated in carbonates

( i l it ) C idCa 1490 < D.L.

(mainly magnesite). Consider-Mg 45800 47000

ing high Mg/Si in the solutionAl 133 469

10(k)

and low (< 100 ppm) AsNaH2PO4 Si 13400 22700

3 #

(( pp )

concentration in magne-site(1.0 M) Mn 574 441

k3g

determined by EPMA (< 100 (1.0 M) Mn 574 441

Fe 368 14005

determined by EPMA ( 100

ppm) As in the phosphate

Fe 368 1400

As 108 135 5ppm), As in the phosphate

leaching solution is mainly from

As 108 135

HF/HNO3 leaching solution is mainly from

As adsorbed on antigorite

HF/HNO3

(Total)As 357 756

0As adsorbed on antigorite.(Total)

0

Arsenic fraction adsorbed on antigorite estimated from leachingArsenic fraction adsorbed on antigorite estimated from leaching

experiments by phosphate solution is 20 30% The fraction may regulate5

experiments by phosphate solution is 20-30%. The fraction may regulate

As concentration in groundwater through the adsorption desorption -5

2 4 6 8 10 12

As concentration in groundwater through the adsorption-desorption

ti i A i th h t h b i i l A th f ti 2 4 6 8 10 12k (angstrom-1)

reaction, since As in other host phase may be minimal. Another fraction

(70 80%) b i t d i th t t f ti it Th k (angstrom-1)

Fig 4 Extended XAFS spectra in k and R sp(70-80%) may be incorporated in the structure of antigorite. The average

Fig. 4 Extended XAFS spectra in k and R sp

As(III) solution and As(III) adsorbed on Fe(local structure of As in antigorite is estimated from EXAFS as shown in

As(III) solution, and As(III) adsorbed on Fe(

l h f BH 4 d BH 5Fig. 4 and Table 2.

were also shown for BH-4 and BH-5.g

CONCLUSIONSCONCLUSIONS Ayotte J D eAyotte, J.D. eet al (2005) GArsenic in serpentinites is mostly As (III) The coordination number of et al. (2005) Gand Kinniburg

Arsenic in serpentinites is mostly As (III). The coordination number ofand Kinniburg(1993) ChAs calculated from extended XAFS spectra is ~ 4 suggesting that (1993) ChemAs calculated from extended XAFS spectra is 4, suggesting that

S f 30 % fAs occupies the Si site of antigorite. Approximately ~ 30 % of As ins occup es t e S s te o a t go te pp o ate y 30 % o s

serpentinites is adsorbed on the surface of antigorite Highserpentinites is adsorbed on the surface of antigorite. HighThe study is

concentrations of As in groundwaters in the area are explained byThe study isCanada andconcentrations of As in groundwaters in the area are explained by

f f f f fCanada and

the resorption of As from the surface of antigorite and the release oft e eso pt o o s o t e su ace o a t go te a d t e e ease o

As during the alteration of serpentinites to talc carbonate rocksAs during the alteration of serpentinites to talc-carbonate rocks.

S i ti f A i i Speciation of Arsenic in Speciation of Arsenic in p

orthern Vermont USAorthern Vermont, USAorthern Vermont, USAYoshio TAKAHASHI2 & Peter C RYAN3Yoshio TAKAHASHI2 & Peter C RYAN3

wa Ontario Canada (*khattori@uottawa ca)wa, Ontario, Canada (*khattori@uottawa.ca)

oshima University Higashi-Hiroshima Japanoshima University, Higashi-Hiroshima, Japan

Vermont U S AVermont, U.S.A.

TRACTTRACTAyotte et al 2003) Ryan et al (2009) reported that hydrated ultramafic rocks contain high concentrations of AsAyotte, et al. 2003). Ryan et al. (2009) reported that hydrated ultramafic rocks contain high concentrations of Asltramafic rocks are common in the Appalachians in New England We investigated the occurrence of As inltramafic rocks are common in the Appalachians in New England. We investigated the occurrence of As inth i ti f li h d thi ti l t b i l i (EPMA) f i l id l hi fthe examination of polished thin sections, electron probe microanalysis (EPMA) of minerals, acid leaching of. EPMA and micro-XAFS analyses showed that antigorite is the major host of As. In the phosphate leachingy g j p p gt is suggested that As in the local ground water may be equilibrium with the adsorbed As . XANES spectra at Ast is suggested that As in the local ground water may be equilibrium with the adsorbed As . XANES spectra at Asat the As has a tetrahedral coordination indicating that As is in the Si-site of antigorite EPMA data indicate aat the As has a tetrahedral coordination, indicating that As is in the Si-site of antigorite. EPMA data indicate aeffect: Fe(III) as Fe(III) + As(III) = Mg(II) + Si(IV) in antigorite Our earlier study of serpentinites in north westerneffect: Fe(III) as Fe(III) + As(III) = Mg(II) + Si(IV) in antigorite. Our earlier study of serpentinites in north western

lt f th t di t th t h d ti lt fi k bl f fi i b th A (III) d A (V) ie results of these studies suggest that hydrating ultramafic rocks are capable of fixing both As(III) and As(V) ins in the hydrating fluids.s e yd a g u ds

and OBJECTIVESand OBJECTIVESld It is ubiquitously present in the earth crust and may enter human or live stocks’ diets through drinking waterld. It is ubiquitously present in the earth crust and may enter human or live stocks diets through drinking water,

n the areas underlain by ultramific rocks in Vermont contain high concentration of As We investigaged the hostn the areas underlain by ultramific rocks in Vermont contain high concentration of As. We investigaged the host

orporation process of As in the rock and the source of high concentration of As in groundwater.sp p g g

HODSHODS

Electron probe micro analysis (EPMA)Electron probe micro-analysis (EPMA)

Micro X-ray absorption analysisMicro X ray absorption analysis

Thin

section - Acid leaching followed by ICP-AES and - Acid leaching followed by ICP-AES and

ICP-MS analysisS l

ICP MS analysisSample

- X-ray diffraction (XRD) analysisM tit

- X-ray diffraction (XRD) analysisMagnetite

Serpentine S nchrotron based X ra absorptionSerpentine - Synchrotron-based X-ray absorptionCrushed rock sample

y y p

analysisCrushed rock sample analysis

d DISCUSSIONd DISCUSSIONd DISCUSSION

contents of As in Cr-spinel and Fecontents of As in Cr-spinel and Fe

it f 100 Th i lmits of ~ 100 ppm. These minerals

eas antigorite shows a positive peak.g p p

nti

on

Antigorite at

Point 41 in Grain E orp

tt go te at

Point 41 in Grain E

of BH5 bso

d a

bze

dm

aliz

orm

No

As standard

Fi 4 XAFS l i f b lk k l Th l t t f diff tFig. 4 XAFS analysis of bulk rock sample. The valence states of different

samples were compared to As(III) and As(V) standards. The vertical line

indicated the absorption peak of As(III).

The major As specie presented in the samples is As (III) inThe major As specie presented in the samples is As (III) inti

spinel (dark gray) rimmed by magnetite (white)serpentine.

p ( g y) y g ( )

ed to that of As standard.

solution

Table 2. EXAFS parameters for BH-4 and BH-5.Shell R (Å) CN DW (Å) !E (eV)

Table 2. EXAFS parameters for BH 4 and BH 5.

25 OShell R (Å) CN DW (Å) !E (eV)

As-O 1 780 0 009 4 0 0 5 0 070 0 01625 As-O 1.780 0.009 4.0 0.5 0.070 0.016

8 9 2 0BH 4 As Si 3 204 0 070 0 6 0 1 0 075* 8.9 2.0BH-4 As-Si 3.204 0.070 0.6 0.1 0.075

As Mg 3 491 0 031 1 9 0 9 0 075*

20As-Mg 3.491 0.031 1.9 0.9 0.075*

As O 1 775 0 009 3 9 0 5 0 069 0 016

de

Fe

As-O 1.775 0.009 3.9 0.5 0.069 0.016

8 0 2 0BH 5 As Si 3 188 0 062 0 7 0 6 0 075*

tud Fe

A (III) F (OH)

8.0 2.0BH-5 As-Si 3.188 0.062 0.7 0.6 0.075*

As Mg 3 484 0 032 1 8 0 9 0 075*

15gn

i As(III) on Fe(OH)3 As-Mg 3.484 0.032 1.8 0.9 0.075*

mag Coordination number (CN) and the distances between As

FT

m

Si Mg

( )and O indicate that As(III) has a tetrahedral coordination in

10

F Sig

BH-5and O indicate that As(III) has a tetrahedral coordination inantigorite Peaks of second and third shells in R space in BH-antigorite. Peaks of second and third shells in R space in BH-4 and BH 5 are weaker than that that of As on Fe(OH)

SiMg

BH 4

4 and BH-5 are weaker than that that of As on Fe(OH)3,ti th t F i t i ifi t i th h ll Th5

Si BH-4 suggesting that Fe is not significant in the shells. Thecalculated distances for As-O, As-Si, and As-Mg are longer

AsO33- solution

, , g gthan Si-O (1 65-1 65 ) Si-Si (3 0-3 1 ) and Si-Mg (3 4 )

00 1 2 3 4 5

AsO3 solution than Si O (1.65 1.65 ), Si Si (3.0 3.1 ) and Si Mg (3.4 )of antigorite The As O bonding is distorted compared with Si0 1 2 3 4 5

R (angstrom)of antigorite. The As-O bonding is distorted compared with Si-O t t h d b t th d d thi d h ll i il tR (angstrom)

paces for As in bulk rock sample (BH 4 and BH 5)O tetrahedra, but the second and third shells are similar to

paces for As in bulk rock sample (BH-4 and BH-5),

(OH) Simulation results using FEFF parametersthose of As-free antigorite.

(OH)3. Simulation results using FEFF parametersg

REFERENCESREFERENCESet al (2003) Environ Sci Technol 37 2075-2083 Dolan B L (1996) Rocks & Minerals 71(4) Hattori Ket al. (2003) Environ. Sci. Technol., 37, 2075-2083. Dolan, B.L. (1996) Rocks & Minerals, 71(4). Hattori, K. Geochim Cosmochim Acta 69 5585 5596 Ryan P C et al (2009) Abst GSA Mtg 77 3 Smedley P LGeochim. Cosmochim. Acta, 69, 5585-5596. Ryan, P.C. et al. (2009) Abst. GSA Mtg., 77-3. Smedley, P.L. gh D G (2002) Appl Geochem 17 517 568 Takahashi et al (1987) Chinetsu 24 69 75 Yokoyama et algh, D.G., (2002) Appl. Geochem. 17, 517–568. Takahashi et al., (1987) Chinetsu, 24, 69-75. ,Yokoyama et al., i l G l 103 103 111mical Geology, 103,103-111.

ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS

s supported by a Discovery Grant to KH from the Natural Science and Engineering Research Council ofs supported by a Discovery Grant to KH from the Natural Science and Engineering Research Council of d a grant in aid for scientific research to YT from Japan Society for the Promotion of Scienced a grant-in-aid for scientific research to YT from Japan Society for the Promotion of Science.