Journal of Nuclear and Radiochemical Sciences, Vol. 23, pp. 14-19, 2023

ArticlesArsenic and iron speciation and binding in the surface soils in Ningyo-toge mill tailings
pond using X-ray absorption fine spectroscopy
Kohei Tokunagaa,b,*, Yoshio Takahashic and Naofumi Kozaia,ba

Ningyo-toge Environmental Engineering Center, Japan Atomic Energy Agency, Tomata, Okayama 708-0698,
Japanb
Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japanc
Department of Earth and Planetary Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
Received May 12, 2023, Accepted July 11, 2023; Published online July 26, 2023
The mobility of arsenic (As) in the environment is generally controlled by its association with iron minerals
through adsorption, coprecipitation, or surface precipitation. In this study, the host phases of As in the surface
soil of a mill tailings pond in Ningyo-toge center (Okayama, Japan) were determined using X-ray absorption finestructure (XAFS) spectroscopy. The XAFS analyses showed that (i) Fe is mainly present as Fe(III) (hydr)oxides
such as ferrihydrite and goethite, (ii) As occurs as As(V) and may be retained on such (hydr)oxides via adsorption, and (iii) ferrihydrite and goethite are the host phases of As in the surface soil. Although As(V) retention by
ferrihydrite in this mill tailings pond has already been reported, this is the first study to demonstrate As(V) retention by goethite in the field.
Keywords: arsenic, ferrihydrite, goethite, adsorption, XAFS

1. Introduction
The Ningyo-toge uranium (U) mine area, located at theboundary between Okayama and Tottori prefectures in Japan,
houses the first U mines to be established in Japan1. After theter mination of mining activit y in 2001, Ning yo-toge
Environmental Engineering Center of the Japan Atomic
Energy Agency (hereafter, Ningyo-toge center) has managed
and maintained the mine sites to prevent environmental contamination. At Ningyo-toge center, groundwater is in contact
with U ore-forming minerals (uraninite, ningyoite, coffinite,
and autunite) and contaminated with toxic and/or radioactive
elements, such as U, radium (Ra), and arsenic (As), via contact
with the U ore-forming minerals f lows into a mill tailings
pond. Since groundwater contains iron (Fe) and manganese(Mn) in the form of Fe(II) and Mn(II) ions, Fe(III) andMn(IV) (hydr)oxides are formed over the mill tailings pond
after the exposure of groundwater to the atmosphere. The
concentrations of the aqueous contaminants in the mill tailings
pond water are lower than those in the contaminated groundwater and the maximum acceptable concentrations. It is
assumed that the (hydr)oxides precipitated in the mill tailings
pond remove the contaminants from the contaminated groundwater2,3. However, the detailed mechanism of heavy metals
retention in the soils in Ningyo-toge mill tailings pond has notbeen fully understood.
Arsenic, as well as U and Ra, are problematic elements in
the Ningyo-toge center. Arsenic is a ubiquitous element foundin the atmosphere, soils and rocks, natural and industrial
waters, and living organisms 4. It exists in various oxidation
states (-III, 0, III, V) and mostly dissolves in water as arsenite(AsO2−) and arsenate (AsO 43−). The migration of As in theenvironment has been extensively studied4-10. Arsenic often
occurs with sulfide and Fe(III) minerals in mill tailings as
scorodite (FeAsO 4·2H 2O) and arsenopyrite (FeAsS), respectively, and is enriched in sediments by adsorption, coprecipita*Corresponding author. E-mail: tokunaga.kohei@jaea.go.jp

tion, or surface precipitation on iron (hydr)oxides 4,7,9.
Arsenic-bearing iron (hydr)oxides, such as ferrihydrite (HFO),
goethite (α-FeOOH), and hematite (α-Fe2O3), which play animportant role in the retention of As, are typically found inoxidized sediments4, 5, 10.
The purpose of this study is to elucidate the solid phases
responsible for As retention and thus, establishes a measure forthe safe closure of U mining-related facilities, including themill tailings pond in Ningyo-toge center. Kawamoto et al.
(2021) 2 investigated the speciation of As and Fe in surface soil
samples in the field by X-ray absorption near-edge structure(XANES) analysis and found the presence of As and Fe in
soils as As(V) and Fe(III), respectively, and that As(V) is preferentially adsorbed on ferrihydrite. However, the previous
study lacked information on the local structure of As and Fe in
the soils, and the detailed mechanism of As retention is still
unknown in term of whether As is adsorbed on ferrihydrite orother iron (hydr)oxides. Therefore, we investigated the local
structure of As and Fe in the soil and compared it with synthetic As-adsorbed iron minerals to identify the host phases of
As in the natural soils collected in Ningyo-toge mill tailings
pond. The extended X-ray absorption fine structure (EXAFS)
method was used to determine the binding sites of Fe and As
in soils at the field site.
2. Materials and methods
2.1. Ningyo-toge soil samples. Natural soil and water samples were collected from the mill tailings pond at Ningyo-togecenter in Okayama, Japan (Fig. 1a). The sampling site wasflooded soil located about 150 m downward from the mine pit(Fig. 1b). Surface soil (0–10 cm) and water were collectedusing a plastic spatula in November 2022. The pH and redox
potential (E h) were measured in situ using a glass electrode(9615S-10D; Horiba, Kyoto, Japan) and an ORP electrode(9300-10D; Horiba), respectively. The measured pH and Ehvalues of the surface soil were 5.2 and 482 mV, respectively.

© 2023 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 07/26/2023

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J. Nucl. Radiochem. Sci., Vol. 23, 2023

Tottori

Okayama

(a)
(c)
Fe3+

1

Former open-pit
mine site

1

E /V

0.5
Fe2+

HAsO42-h

Fe(OH)3

h

E /V

0.5

H2AsO4-0

0

AsO43---- Water path
〇 Sampling site

H3AsO4

Toge tunnel No.2
water collecting pit

H3AsO3

Fe(CH3COO)3-0.5

Mill tailings pond

(b)

-0.5

Siderite

FeCH3COO+

Magnetite

0

2

4

6

pH

8

H2AsO3-

FeO

10

12

0

14

2

4

6

pH

8

HAsO32-

10

12

14

Figure 1. (a) Location of U mines around the Ningyo-toge area near the boundary of the Tottori and Okayama prefectures in Japan. (b)Schematic diagram of the Ningyo-toge Environmental Engineering Center of Japan Atomic Energy Agency showing the location of the samplingsite. (c) Eh-pH diagrams of the Fe-CO2-H2O (Fe = 1 × 10 –3 mol L –1, pCO2 10 –3.5 atoms at 25 ℃) and As-H 2O (As = 1 × 10 –3 mol L –1 at 25 ℃) systems showing the equilibrium stability fields for iron phases and arsenic species, plotted with Geochemist’s Workbench 12.0 based on the thermodynamic data from GWB, Aqueous Solutions LLC.

2.2. Water and soil analysis. The As and Fe concentrations in the water samples were measured by inductively coupled plasma mass spectrometry (ICPMS, 7800cs; Agilent,Tokyo, Japan). Concentrations of major elements in the soil
were measured by X-ray f luorescence spectrometry (EDX8100; Shimadzu Corp., Japan). The As concentrations in thesoil samples were determined by digesting the samples with
HNO3/HF fluids under heat treatments, and the filtered solution was analyzed using ICPMS. The mineralogy and morphologies of the samples were studied by X-ray diffraction(XRD, MiniFlex; Rigaku Corp., Japan). The XAFS analysis
was also conducted to investigate the speciation and bindingsites of As and Fe in the soil.
2.3 Preparation of the As adsorbed samples. Two-line
ferrihydrite, goethite, hematite, and siderite (FeCO3) wereselected as iron minerals for XAFS analysis. As shown in
Fig. 2, ferrihydrite and goethite were detected in the soil.
Hematite was selected as the most common Fe(III) minerals.
Siderite was also selected because it was detected by XRD in

Q

Q

Intensity

To maintain the original chemical composition of the samples before measurements, collected soil samples were dried ina glove box (Coy Laboratory Products Inc., USA) under anaerobic nitrogen conditions (< 10 ppm of O2) at room temperature
where little transformation of iron minerals, such as ferrihydrite to goethite and hematite or siderite to goethite, occurs.
The dried soil samples were then passed through a 500 μm
stainless steel sieve to remove large organic particles andgravel fractions, prior to measurements. The homogenizedsoil samples were packed into polyethylene bags under anaerobic conditions and stored at 4 °C until X-ray absorption finestructure (XAFS) analysis. The water samples were filteredthrough a mixed cellulose ester membrane filter with a poresize of 0.20 μm (Advantec, Tokyo, Japan). The filtrate wasacidified to 2 wt % HNO3 by adding concentrated HNO3.

F

M

F

G

F

20

Q

Q

G
F
G
F

10

F

G

F
F

Q

F
F

30

G F

Q
Q

40

2 / degree

Q
Q
G

F G

50

G
G

60

Figure 2. X-ray diffraction patterns of the surface soil sample (M,mica; F, feldspar; Q, quartz; G, goethite).

the soil sample collected several meters below the surface(data not shown). Two-line ferrihydrite, goethite, and siderite
were synthesized following the method described in previous
studies11,12 . The hematite was purchased from STREM
Chemicals Inc. As-adsorbed ferrihydrite, goethite, and hematite samples were prepared by exposing 100 mg of the minerals
to KH 2AsO 4 (Wako, Japan) solution (1 mmol L−1, pH 5.0, 50mL) for 48 h at 25°C under ambient atmospheric conditions.
The solids were collected using a 0.20 μm membrane filter,
washed three times with ultrapure water, and stored at 4 °C
until XAFS analysis. The mineral phases of the synthesized
samples were characterized by XRD with Cu Ka radiation at
40 kV voltage and 40 mA current. The solid samples were airdried under atmospheric and anaerobic conditions before each
XRD measurement.

J. Nucl. Radiochem. Sci., Vol. 23, 2023

Arsenic and iron speciation and binding in the surface soils in Ningyo-toge

The amount of As adsorbed on the solids (C s, mmol kg−1)
and the distribution coefficient (Kd , L kg−1) were calculatedusing the following equations:Cs = |Ci – Ce|•V/m,ters used for LCF are R-factor, which is defined by
R factor = Σ (data − fit)2 /Σ data2
where the low R-factor represents a better match between thestandard spectra and the sample spectrum.

Kd / L kg−1 = Cs/Ce,
where Ci and Ce are the As concentrations in solution before
and after the adsorption (mmol L−1), respectively, V is the volume of liquid (L), and m is the weight of solid (kg).
2.4. XAFS measurement. Bulk Fe and As K-edge XAFS
spectra of the samples were measured at the BL12C of
KEK-PF (Ibaraki, Japan) with a Si(111) double-crystal monochromator and two mirrors. The XANES and EXAFS wereobtained using the XAFS analyses. The monochromator wascalibrated using reference samples, i.e., synthetic goethite andKAsO2 (Wako, Japan), which was prepared as a pellet after
dilution with boron nitride powder. The energy values of 7.111
and 11.865 keV were assigned to the pre-edge and main-edge
peaks in the XANES region of the compounds of Fe and As,
respectively. XAFS spectra of the reference samples were collected in transmission mode, while those of the experimental
samples were obtained in the f luorescence mode using a19-element germanium semiconductor detector placed at 90°
to the incident beam.
The EXAFS spectra were analyzed by normal procedures
using REX2000 software (Rigaku Co. Ltd.) with the parameters generated by the FEFF 7.0 code. Following backgroundsubtraction and normalization, EXAFS oscillations k 3 χ(k)were extracted from the raw data. After extracting EXAFS
oscillations and their Fourier transformations, the inversely
Fourier filtered data were analyzed using a conventional curve
fitting method.
XANES linear combination fitting (LCF) was performed toquantify the relative abundance of Fe and As species in thesoils. Solid-phase Fe and As speciation was further evaluatedby fitting of k 3 weighted EXAFS spectra of soil samples
against corresponding spectra from references using theAthena interface to IFEFFIT13. The goodness of fit parame-(a)3. Results and discussion
3.1. Soil and water characterization. The properties ofthe soil samples were summarized in Table 1. The soil contained high levels of Si (57.1 wt.%), Fe (17.7 wt.%), and Al(15.7 wt.%). The As concentration of the soil (1.1 × 10 3
mg kg−1) was about five orders of magnitude higher than thatof the water (2.3 × 10 −2 mg L−1), indicating that the As in thewater flowing into the mill tailings pond was enriched in thesurface soil. Arsenic-bearing minerals, such as scorodite and
TABLE 1: Chemical composition of the surface soil andwater in Ningyo-toge mill tailings pond.
Element

Soil / %Pond water

Si
Fe
Al
Ca
Ti
Na
S
P
Cu
Sr
Mn
Total

57.1
17.7
15.7
4.0
2.7
1.5
0.31
0.24
0.22
0.20
0.10
99.8
mg kg-1
1.1×103
1.6×105

mg L-1
2.3×10 -2
1.7×100AsFe

78% Fh. + 22 % Gt.

(b)・SampleFit

Soil sample

Fh.

Gt.

Soil sample

(k) k3

Normalized Absorption

16

Fh.
Gt.

Hm.

Hm.

Sid.
Sid.

7.10 7.11 7.12 7.13 7.14 7.15 7.16

Energy / eV246k / Å-1

8

10

Figure 3. (a) Fe K-edge XANES spectra of the soil sample and references. Two Line-ferrihydrite, goethite, hematite, and siderite are present asFh., Gt., Hm., and Sid., respectively. The black broken lines indicate the binding energy of the main peak of two-line-ferrihydrite. (b) Fe K-edge
EXAFS spectra of the soil sample and references.

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J. Nucl. Radiochem. Sci., Vol. 23, 2023

arsenopyrite, were not observed in the XRD spectrum of thesoil (Fig. 2). The major crystalline minerals in the soil werequartz, albite, mica, and goethite. Although Fe was enrichedin the soil, goethite was a minor component, and other ironminerals were not observed in the XRD patterns. Such Fe
enrichment may have been due to the presence of ferrihydritein the soil, which is not detected by XRD analysis because of
its amorphous structure.
The formation of iron phases and aqueous As species can be
estimated from pH‑Eh diagrams. Considering the pH (5.2) andE h (482 mV) values recorded at the site (Fig. 1), iron (hydr)oxides such as ferrihydrite, goethite, and hematite are the predicted stable phase and As occurs as As(V) (H 2 AsO 4 −) inaqueous solution.

hematite, and siderite samples were investigated by EXAFS.
The Kd values of As for these iron minerals determined by theadsorption experiments are summarized in Table 2. The
Fourier transformation of EXAFS spectra (figure not shown)is consistent with previous EXAFS studies for As(V) on ferrihydrite14,15, goethite14-16, hematite14, and siderite14,15. The As
K-edge k3 weighted EXAFS spectra of the soil sample and references are shown in Fig. 4b.
According to the LCF of the k3 weighted EXAFS spectra (inthe 2.8−11.5 Å–1 range), the As fractions of each binding site in
the sample are estimated to be As(V)-adsorbed ferrihydrite(70%) and As(V)-adsorbed goethite (30%), in accordance with
the LCF results of Fe K-edge XAFS spectra. Figure 4(c)shows the comparison of LCF results obtained from (i) As(V)adsorbed ferrihydrite (70%) and As(V)-adsorbed goethite(30%) (R=0.08), (ii) As(V)-adsorbed goethite (R=0.20), and(iii) As(V)-adsorbed ferrihydrite (R=0.12). The best fits of thesample are obtained from (i), as indicated by the low R factor,
due to the specific features of EXAFS oscillations of the sample at k around 4.8 and 7.2 Å–1. These results indicate that both
ferrihydrite and goethite are the host phase of As in the surface soil and that the As flowing into the Ningyo-toge milltailings pond is removed from the water mainly by adsorption.
This is the first study to demonstrate the occurrence of As(V)adsorbed goethite in Ningyo-Toge mill tailings pond.

3.2. XAFS Analyses for Fe and As. The Fe species in thesoil samples were characterized by XAFS at the Fe K-edge.
The features around the absorption edge of the sample aresimilar to those of ferrihydrite and differ from those of theother Fe minerals (Fig. 3a). The fraction of the Fe phases wasdetermined by the LCF analysis of the k 3 weighted EXAFS
oscillations (in the 2.5−8.8 Å–1 range) of the samples against
corresponding spectra from references including ferrihydrite,
goethite, hematite, and siderite (Fig. 3b). The amplitude of thek3 χ(k) function at k around 5–6 Å–1 clearly differs in all references, and the Fe fractions of the soil sample are estimated to
be ferrihydrite (78%) and goethite (22%) (R=0.09). These
results indicate that the major oxidation state of Fe is Fe(III),and Fe is mainly present as Fe(III) (hydr)oxides such as ferrihydrite and goethite in the surface soil.
Figure 4a shows the As K-edge XANES spectra for references and the soil sample. The XANES spectrum of the sample was very similar to that of KH 2AsO4, suggesting that As
exists as As(V) in the soil. This is in agreement with the mainchemical species of As in water (H 2AsO4−, As(V)) estimatedfrom the pH and Eh values at the site (Fig. 1c).
The local structure of As was examined by EXAFS to
obtain information on the host phases of As(V) in the soil. As
reference samples, the As(V)-adsorbed ferrihydrite, goethite,

3.3. As mobility in Ningyo-toge mill tailings pond. This
study showed that the soil As(V) samples are associated withiron (hydr)oxides that have high adsorption capacity and affinity for heavy metals, including As. However, the cause foradsorption of As(V) on both ferrihydrite and goethite remains
unclear. Previous studies have shown that goethite has a low
adsorption capacity for As(V) compared with ferrihydrite4,17,18.
This study also revealed that the Kd value for goethite wasapproximately three orders of magnitude lower than that for
ferrihydrite (Table 2). However, the XAFS results showed theoccurrence of As(V)-adsorbed ferrihydrite (70%) and As(V)adsorbed goethite (30%) in the mill tailings pond, which is inconsistent with the adsorption capacity of the iron (hydr)

As(V)-Fh. (70%)+ As(V)-Gt. (30%)(R = 0.08)

・Sample
Fit

(b)

(c)

Soil sample

(i)

(i)

(k) k3

Normalized Absorption(a)As(V)-Fh. (R = 0.13)

KH2AsO4
Soil sample

(ii)

(ii)
(iii)

(iii)

(iv)

KAsO2

11.85

As(V)-Gt. (R = 0.20)

11.86

11.87

Energy / eV

11.88 24

68

k / Å-1

10

12 2

4

6

8

10

12

Figure 4. (a) As K-edge XANES spectra of soil sample and references. The red broken lines indicate the binding energy of main peak of
KH2AsO4, respectively. The blue broken line indicates the binding energy of the main peak of KAsO2. (b) As K-edge EXAFS spectra of the soil
sample and As(V)-adsorbed samples. As(V)-adsorbed samples of (i) As(V)-adsorbed Fh., (ii) As(V)-adsorbed Gt., (iii) As(V)-adsorbed Hm.,and (iv) As(V)-adsorbed Sid. (c) Experimental spectra of the soil sample and calculated fits using linear combination fitting (LCF) obtained
from (i) As(V)-adsorbed ferrihydrite (70%) and As(V)-adsorbed goethite (30%) (R=0.08), (ii) As(V)-adsorbed ferrihydrite (R = 0.13), and (iii)
As(V)-adsorbed goethite (R = 0.20).

J. Nucl. Radiochem. Sci., Vol. 23, 2023

Arsenic and iron speciation and binding in the surface soils in Ningyo-toge

18

TABLE 2: Adsorption capacity of As(V) for iron minerals.
SamplesCi/ mmol L-1

Ce/ mmol L-1

Qs/ mmol kg-1

Kd/ L kg-1

2 Line ferrihydrite (oxic)

1.3×100

2.0(±0.2)×10 -2

6.2(±0.0)×102

3.2(±0.2)×104

Goethite (oxic)

1.3×1008.9(±0.2)×10-11.9(±0.1)×102

2.1(±0.1)×102

Hematite (oxic)

1.1×100

1.0(±0.2)×100

3.5(±1.0)×101

3.5(±1.0)×101

Siderite (anoxic)

1.3×100

1.2(±0.0)×10 -2

5.9(±0.0)×102

4.9(±0.0)×104

oxides under experimental conditions. Previous studies havealso shown that As(V)-adsorbed ferrihydrite transforms togoethite and hematite with time10,19,20, and a large amount ofAs(V) is believed to be released into solution and doesn’t
remain adsorbed on the goethite surface during the transformation5,19,21-23. Therefore, it is considered that As(V)-adsorbed
goethite in the field site is not formed by the simple adsorptionof As(V) on goethite and transformation of As(V)-adsorbed
ferrihydrite to goethite.
The enrichment of As(V) in goethite may be due to several
factors, such as abiotic and biotic features of the environment.
We considered (i) the interaction of organic matter with mineral surfaces24 and (ii) the transformation of other iron minerals (e.g., siderite12,25,26 and schwertmannite27,28) to goethite. For
example, one hypothesis is based on the transformation of siderite, which is detected in the several meters below the surface(data not shown), to goethite. Previous studies have shownthat the transformation of siderite to goethite from anoxic tooxic conditions increases the adsorption capacity of As(V) on
goethite by an order of magnitude12,25. Thus, it is consideredthat siderite precipitated in deep soils under anoxic conditionstransforms to goethite in surface soils under oxic conditions,and then the enrichment of As(V) in goethite occurs during
the transformation. This is a hypothesis and the details of the
As retention behavior in the field remain unknown, and will
be a topic of our future research.
4. Conclusions
This study revealed that both ferrihydrite and goethite are
the host phases of As in the surface soils in Ningyo-toge milltailings pond. To the best of our knowledge, this is the firststudy to investigate the local structure of Fe and As in soils
collected in the mill tailings pond by EXAFS analysis. The
novelty of this study is that some of the As can be stabilized byadsorption on goethite and occurs as As(V)-adsorbed goethite
in the surface soils. These results indicate that As flowing
into the Ningyo-toge mill tailings pond is removed from water
mainly by adsorption on ferrihydrite and goethite in the field.
These findings would help remediate contaminated soils andpredict the long-term behavior of As in the natural environment.
Acknowledgements
This work was carried out under the approval of the Photon
Factory (nos. 2021G076 and 2022G512). Financial support
was partly provided by JSPS KAKENHI Grant Number JP
23K13693 and by ERAN Y-23-04. This study was also partly
p e r fo r m e d u n d e r t h e s u b sid y p r og r a m “ P r oje c t of
Decommissioning, Contaminated Water and Treated Water
Management (Research and Development of Processing andDisposal of Solid Waste)” conducted by the Ministry of
Economy, Trade and Industry of Japan.
References[1]	Muto T, Meyrowitz R, Pommer AM, Murano T (1959)

Ningyoite, a new uranous phosphate mineral fromJapan. American Mineralogist: Journal of Earth andPlanetary Materials, 44(5-6): 633–650.
[2]	Kawamoto K, Yokoo H, Ochiai A, Nakano Y, Takeda A,
Oki T, Takehara M, Uehara M, Fukuyama K, Ohara Y,
Ohnuki T, Hochella MF, Utsunomiya S (2021) The roleof nanoscale aggregation of ferrihydrite and amorphoussilica in the natural attenuation of contaminant metals at
mill tailings sites. Geochim Cosmochim Acta, 298: 207–226.
[3]	Takeda A, Oki T, Yokoo H, Kawamoto K, Nakano Y,
Ochiai A, Winarni ID, Kitahara M, Miyoshi K,
Fukuyama K, Ohara Y, Yamaji K, Ohnuki T, Hochella
MF, Utsunomiya S (2023) Direct observation of Mn distribution/speciation within and surrounding a basidiomycete fungus in the production of Mn-oxides important in
toxic element containment. Chemosphere, 313: 137526.
[4]	Smedley PL, Kinniburgh DG (2002) A review of thesource, behaviour and distribution of arsenic in natural
waters. Applied geochemistry, 17(5): 517–568.
[5]	Majzlan J, Lalinská B, Chovan M, Jurkovič LU,
Milovská S, Göttlicher J (2007) The formation, structure,
and ageing of As-rich hydrous ferric oxide at the abandoned Sb deposit Pezinok (Slovakia). Geochim
Cosmochim Acta, 71(17): 4206–4220.
[6]	Mitsunobu S, Harada T, Takahashi Y (2006) Comparisonof antimony behavior with that of arsenic under various
soil redox conditions. Environ Sci Technol, 40(23):7270–7276.
[7]	Yamaguchi N, Nakamura T, Dong D, Takahashi Y,
Amachi S, Makino T (2011) Arsenic release from flooded
paddy soils is influenced by speciation, Eh, pH, and irondissolution. Chemosphere, 83(7): 925–932.
[8]	Tokunaga, K, Uruga, T, Nitta, K, Terada, Y, Sekizawa, O,
Kawagucci, S, Takahashi, Y (2016) Application of arsenic in barite as a redox indicator for suboxic/anoxic redox
condition. Chem Geol, 447: 59–69.
[9]	Itabashi T, Li J, Hashimoto Y, Ueshima M, Sakanakura
H, Yasutaka T, Imoto Y, Hosomi, M (2019) Speciationand fractionation of soil arsenic from natural and anthropogenic sources: chemical extraction, scanning electron
microscopy, and micro-XRF/XAFS investigation.
Environ Sci Technol, 53(24): 14186–14193.
[10]	Shi M, Min X, Ke Y, Lin Z, Yang Z, Wang S, Wei Y(2021) Recent progress in understanding the mechanismof heavy metals retention by iron (oxyhydr) oxides. Sci
Total Environ, 752: 141930.
[11]	Cornell RM, Schwertmann U (2003) The iron oxides:
structure, properties, reactions, occurrences, and uses
(Vol. 664). Weinheim, Germany.
[12]	Guo H, Ren Y, Liu Q, Zhao K, Li Y (2013) Enhancementof arsenic adsorption during mineral transformation fromsiderite to goethite: mechanism and application. Environ
Sci Technol, 47(2): 1009–1016.
[13]	Newville M (2001) EXAFS analysis using FEFF andFEFFIT. Journal of synchrotron radiation, 8(2): 96–100.
[14]	Sherman D M, Randall S R (2003) Surface complexationof arsenic (V) to iron (III)(hydr) oxides: structural mech-

19

J. Nucl. Radiochem. Sci., Vol. 23, 2023

anism from ab initio molecular geometries and EXAFS
spectroscopy. Geochim Cosmochim Acta: 67(22), 4223–
4230.
[15]	Yang S, Uesugi S, Qin H, Tanaka M, Kurisu M,
Miyamoto C, Kashiwabara T, Usui A, Takahashi Y(2018) Comparison of arsenate and molybdate speciationin hydrogenetic ferromanganese nodules. ACS Earth andSpace Chemistry, 3(1): 29–38.
[16]	Jönsson J, Sherman DM (2008) Sorption of As (III) andAs (V) to siderite, green rust (fougerite) and magnetite:
Implications for arsenic release in anoxic groundwaters.
Chemical Geology, 255(1-2): 173–181.
[17]	Ona-Nguema G, Morin G, Juillot F, Calas G, Brown GE(2005) EXAFS analysis of arsenite adsorption onto twoline ferrihydrite, hematite, goethite, and lepidocrocite.
Environ Sci Technol, 39(23): 9147–9155.
[18]	Jiang X, Peng C, Fu D, Chen Z, Shen L, Li Q, Ouyang T,
Wang Y (2015) Removal of arsenate by ferrihydrite via
surface complexation and surface precipitation. Applied
Surface Science, 353: 1087–1094.
[19]	Waychunas GA, Rea BA, Fuller CC, Davis JA (1993)
Surface chemistry of ferrihydrite: Part 1. EXAFS studiesof the geometry of coprecipitated and adsorbed arsenate.
Geochim Cosmochim Acta, 57(10): 2251–2269.
[20]	Catalano JG, Luo Y, Otemuyiwa B (2011) Effect of aqueous Fe (II) on arsenate sorption on goethite and hematite.
Environ Sci Technol, 45(20): 8826–8833.
[21]	Ford RG (2002) Rates of hydrous ferric oxide crystallization and the influence on coprecipitated arsenate. Environ
Sci Technol, 36(11): 2459–2463.

Tokunaga[22]	Erbs JJ, Berquó TS, Reinsch BC, Lowry GV, Banerjee
SK, Penn RL (2010) Reductive dissolution of arsenicbearing ferrihydrite. Geochim. Cosmochim. Acta, 74(12):3382–3395.
[23]	Mitsunobu S, Muramatsu C, Watanabe K, Sakata M(2013) Behavior of antimony (V) during the transformation of ferrihydrite and its environmental implications.
Environ Sci Technol, 47(17): 9660–9667.
[24]	Shu Z, Pan Z, Wang X, He H, Yan S, Zhu X, Song W,
Wang, Z (2022) Sunlight-Induced Interfacial ElectronTransfer of Ferrihydrite under Oxic Conditions: Mineral
Transformation and Redox Active Species Production.
Environ Sci Technol, 56(19): 14188–14197.
[25]	Guo H, Li Y, Zhao K (2010) Arsenate removal from
aqueous solution using synthetic siderite. Journal of hazardous materials, 176(1–3): 174–180.
[26]	Stolze L, Zhang D, Guo H, Rolle M (2019) Model-based
interpretation of groundwater arsenic mobility during insitu reductive transformation of ferrihydrite. Environ Sci
Technol, 53(12): 6845–6854.
[27]	Burton ED, Bush RT, Sullivan LA, Mitchell DR (2008)
Schwertmannite transformation to goethite via the Fe (II)pathway: Reaction rates and implications for iron–sulfide
formation. Geochim Cosmochim Acta, 72(18): 4551–
4564.
[28]	Burton ED, Johnston SG, Kraal P, Bush RT, Claff S(2013) Sulfate availability drives divergent evolution ofarsenic speciation during microbially mediated reductive
transformation of schwertmannite. Environ Sci Technol,47(5): 2221–2229.