NMCC ANNUAL REPORT 20 (2013)

Accumulation of indium derived from acidic thermal water in the sediment at
Tamagawa Dam, Akita prefecture, Japan

Quyen Pham Minh1, Daizo Ishiyama2, Yasumasa Ogawa2, Hinako Sato 2,
Yumi Sato2 and Koichiro Sera 3
1 Graduate School of Engineering and Resource Science, Akita University
2Faculty of International Resource Science, Akita University

1-1 Gakuen-Machi, Tegata, Akita 010-8502, Japan
3 Cyclotron Research Center, Iwate Medical University348-58 Tomegamori, Takizawa, Iwate 020-0603, Japan

Abstract
Variations in the concentrations of major elements (Fe, Al and Si) and trace elements (In andPb) in sediments in Tamagawa Dam, a man-made dam that receives acidic water from Tamagawa
Hot Spring, were investigated. Two sediment samples were collected at an upstream site (pH = 4.7)
and downstream site (pH=4.1) at Tamagawa Dam. The thickness of both sediments wasapproximately 12 cm. The sediments consist of alternation of many layers composed of fine-grained
particles. Indium content in the sediment ranges from 0.39 to 0.79 ppm and the content is7-14-times higher than the average In content in the continental crust. The In-rich layer ischaracterized by high concentrations of Fe and Pb and a low concentration of Al. Based on the
average In content and the amount of sediment at Tamagawa Dam, the estimated amount of In in thesediment is approximately 540 kg since Tamagawa Dam was built in 1990. On the other hand, theamount of In released from Obuki Hot Spring is estimated to be approximately 500 kg based on the
discharge rate (9,000L/min) and In content (0.57 ppb) of Obuki thermal water from 1990 to 2012.
Both estimations are consistent and this fact suggests that most of the In was precipitated in
Tamagawa Dam over the 22-year period.

1 Introduction
Tamagawa Hot Spring consists of many acidic hot springs welling up in a depression area on thewest flank of Yakeyama volcano. Obuki Spring is the main hot spring in Tamagawa Hot Spring. The
pH value of the thermal water is 1.2. The acidic thermal water is drained to Shibukuro River. River
water having an acidic signature flows into neutral river water of Tama River having a neutral pH andruns downstream through Tama River. The water is also harmful to crops in the downstream area.
Tamagawa Dam is located on Tama River 13 km downstream from Tamagawa Hot Spring. Tamagawa
Dam is a concrete gravity dam with a height of 100 m, volume of 1.15 x 106 m3 and area of 7 km2. The
dam was constructed in 1990. River water containing acid thermal water from Tamagawa Hot Springmight dissolve the concrete of Tamagawa Dam. Therefore, acidic thermal water from Obuki Hot Springis transported to a neutralization facility to reduce its acidity by means of neutralization reaction
between the thermal water and limestone. The thermal water after the reaction (pH: around 3) isdischarged into Shibukuro River. Recent studies on the thermal water of Obuki Hot Spring have shown76

NMCC ANNUAL REPORT 20 (2013)that the thermal water contains rare metals such as Ga and In (Satoh et al., 2010; Ogawa et al., 2012).
The In content of the thermal water is 0.57 ppb. The possibility that In is precipitated in the sediments
at Tamagawa Dam was pointed out by Ogawa et al. (2012). However, there have been few studies on
the mode of occurrence and concentration of In in the sediments. Therefore, the aim of this study was toclarify the mode of occurrence of sediments and distribution of In in the sediments and to estimate theamount of In at Tamagawa Dam.

Fig. 1 Location of the study area and sampling points

2 Study area and methods of study
2.1. Characteristics of hot springs in the Tamagawa Hot Spring area
Tamagawa Hot Spring consists of Cl-SO4-type (Obuki) thermal water and SO4-type thermal water.
The thermal water of Obuki Hot Spring is Cl-SO4-type thermal water. The discharge rate, pH and77

NMCC ANNUAL REPORT 20 (2013)

temperature of the thermal water from Obuki Hot Spring are 9000 L/min, 1.2 and 98°C, respectively(Yoshike, 1993). Other hot springs in the Tamagawa Hot Spring area consist of SO4-type thermal watercontaining a small amount of Cl, although the pH of the thermal water is acidic (1.8 to 3.5). The
thermal water of Tamagawa Hot Spring is the main cause of acidification of the Shibukuro-Tama Riversystem.
The SO4-type thermal water is transported to Shibukuro River through Hiyamizu and Yukawa
Streams. The thermal water reduces the pH value of the water of Shibukuro River from 4.3 to 2.8 whenit drains into Shibukuro River (Fig. 1). On the other hand, the Cl-SO4-type thermal water from Obuki
Hot Spring is transported directly to the neutralization plant. The pH value of the thermal waterchanges from 1.2 to 3.5 after neutralization. The thermal water with a pH value of 3.5 is drained into
Shibukuro River and is mixed with water of Shibukuro River having a pH value of 2.8. The water (pH =3.4) of Shibukuro River at Tm 430 joins the water of Tama River (pH = 6.2 at Tm 431) at the confluenceof Shibukuro River and Tama River, and then the pH value of the water of Tama River changes to 3.8 at
Tm 448 (Fig. 1).
The river water flows into Tamagawa Dam located 13 km downstream from Tamagawa Hot Spring.
The pH values of river water at Tamagawa Dam were 4.7 in the middle part (under Ogami Bridge) and
4.1 downstream of the dam (near Taihei Bridge) in October 2012. Samples of sediment at Tamagawa
Dam were obtained in October 2012. The water level of Tamagawa Dam was decreased greatly insummer and fall in 2012 because of the small amount of precipitation. Two sediment samples werecollected from the bottom of Tamagawa Dam at points under Ogami Bridge (Ogami sample, upstreamsite at Tm 450) and near Taihei Bridge (Taihei sample, downstream site at Tm 452) (Fig. 1). Thesesamples were samples of sediment that had been deposited on gravel of the river bed. The bottom of thesediment corresponds to the start of deposition of sediment in 1990 and the top of the sedimentcorresponds to deposition of sediment in 2012. The sediments were formed over the past 22 years.
The sediments consist of alternation of layers composed of fine-grained particles. Both samples
consist of alternation of light gray layers and dark-brownish layers. The thicknesses of Ogami and
Taihei sediment samples were 12 cm and 10 cm, respectively. The Ogami sample consisted of distinctly
banded and poorly banded portions in ascending order. The distinctly and poorly banded portions of thesample consisted 8 layers with a thickness of 3.5 cm and 10 layers with a thickness of 8.5 cm, respectively.
The boundary between these portions of the Ogami sample corresponds to a plane showing cross-bedding(Fig. 2a). On the other hand, the Taihei sample consisted of 20 layers with distinctly banded layers.
The banded layers in the lower parts had a lighter color than those in the upper part of the Taihei sample(Fig. 2b).
2.2. Methods for analysis of sediment samples
Ten Ogami samples and 10 Taihei samples were prepared for examination of mineral assemblage
and chemical composition (Fig. 2). The samples were air-dried and then grained to obtain fine-grained
powder samples. X-Ray diffraction was used to determine the mineral assemblage. The bulk chemicalcompositions of layers of sediment samples were determined by proton-induced X-ray emission (PIXE) at
Nishina Memorial Cyclotron Center and by atomic absorption spectroscopy (AAS) and inductively
coupled plasma mass spectrometry (ICP-MS) at Akita University. Analytical procedures for PIXE and
ICP-MS were described by Sera and Yanagisawa (1992) and Satoh et al. (1999), respectively.

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Fig. 2 Sediment samples from Tamagawa Dam. (a) Sample under Ogami Bridge, (b) Sample near
Taihei Bridge

3 Results
3.1. Density of the sediment
Samples were cut into cubes to determine the density. The mass and volume of samples were
measured (Table 1). The density of the sediment was 1.08 g/cm3, which is approximately one third (1/3)
of the density of normal rocks.
3.2. Mineral assemblages
The sediments of Ogami and Taihei samples consist of clay

Table 1 Density of sedimentminerals: a large amount of montmorillonite and smaller amounts ofillite, kaolinite, chlorite, quartz, cristobalite and albite (Table 2). Thereis a possibility that amorphous materials (amorphous silica, ironhydroxide and others) are included in the sediments.

The mineral

assemblages of Ogami and Taihei samples are similar, though thestructures of these samples are different.
3.3. Geochemical characteristics of sediments
SiO2 contents of Ogami and Taihei samples range from 39.7 to 47.1 and 28.0 to 52.4 wt.%,
respectively. The SiO2 content of the distinctly banded portion of the Ogami sample decreases from thebottom part (45.8 wt. %, OA-1-1) to the middle part (41.8 wt. %, OA-1-5). One layer (OA-2) in the lower
part of the poorly banded portion of the Ogami sample shows the highest SiO2 content (47.1 wt. %), andthe SiO2 content gradually decreases from the OA-2 layer to the top (43.0 wt. %, OB-4) (Table 3, Fig. 3a).
SiO2 content in the Taihei sample is higher than that in the Ogami sample. The SiO2 content increases
from the bottom (39.7 wt.%, A-1) to the A-3-1 layer (52.4 wt. %) and then decreases to the middle part
(approximately 45 wt. %, A-4-1 and A-4-2). SiO2 content increases from the middle part (44.3 wt. %,A-4-2) to the lower part of the upper portion of the Taihei sample (50.2 wt. %, A-5-1) and then decreases
to the upper part of the upper portion (36.2 wt%, A-5-4) (Table 3, Fig. 3b). These variations of SiO2
content in the Taihei sample correspond to the variation in color of each layer in the sample. The layer
having a light brownish color corresponds to higher SiO2 content and the layer having a dark brownish
color shows a lower SiO2 content (Fig. 3b).

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NMCC ANNUAL REPORT 20 (2013)

The Al2O3 content in the Ogami

Table 2 Mineral assemblages determined by XRD analysis

sample ranges from 12.9 to 18.4 wt. %(Table 3, Fig. 3a).

The Al2O3 content

shows distinct variation in the distinctly
banded part of the Ogami sample, and thecontent slightly decreases towards the topof the sample. The variations of SiO2 andAl2O3 contents in the Ogami sample show
similartendencies

Al2O3-rich

layer

(Fig.

3a).

corresponds

The
to

light

brownish color. The layer is composed oflarge amounts of montmorillonite and illite.
The Al2O3 content of the Taihei sample
ranges from 10.6 to 18.3 wt. % (Table 3, Fig.
3b). The range is wider than that of theOgami

sample.

The

Al2O3

content

decreases from the bottom to middle partin the Taihei sample and then increases tothe top of the sample (Fig. 3b).
Fe2O3 contents of the Ogami and
Taihei samples increase from the bottom to
top.

The ranges of Fe2O3 contents arefrom 5.0 to 9.9 wt. % and from 4.8 to 12.7
wt. % in the Ogami and Taihei samples,
respectively. The range of Fe2O3 contents
in the Taihei sample is slightly larger thanthat in the Ogami sample (Table 3, Fig. 3a& 3b).

Fe2O3-rich layers correspond todark reddish brown layers in Ogami and
Taihei samples.
A comparison of the SiO2 and Al2O3 contents in Ogami and Taihei samples with SiO2 and Al2O3
contents of montmorillonite, kaolinite, illite, plagioclase, cristobalite and quartz is shown in Fig. 4. The
SiO2 and Al2O3 contents of the Ogami sample are plotted near the chemical composition of Fe-richmontmorillonite. The distribution suggests that the Ogami sample is composed of a large amount ofFe-rich montmorillonite (Fig. 4). The SiO2 and Al2O3 contents of the Taihei sample are distributed near
the chemical composition of illite and Fe-montmorillonite (Fig. 4). The SiO2 and Al2O3 contents of the
Taihei sample are divided into two groups. The first group is plotted along a line connecting the originof the diagram (Fig. 4) and chemical composition of montmorillonite. SiO2 and Al2O3 contents of thefirst group in the Taihei sample show chemical compositions similar to those of the Ogami sample. The
second group is plotted along a line connecting the origin of the diagram and chemical composition ofillite. The sediment of the Taihei sample does not contain a large amount of illite based on the mineral
assemblage determined by XRD, though the data of SiO2 and Al2O3 contents of the second group in the
Taihei sample are plotted near illite. The distribution of data of the second group does not depend on
the abundance of illite in the samples. These data suggest that the difference between the first and80

NMCC ANNUAL REPORT 20 (2013)

Table 3 Chemical composition of sediments in Tamagawa Damsecond groups in the Taihei sample iscaused by the difference in abundanceof quartz, cristobalite and amorphoussilica in the sample.
Fe-rich layers in the Ogami and
Taihei samples show relatively low
SiO2 and Al2O3 contents.

Data of

SiO2 and Al2O3 contents in theselayers tend are plotted close to theorigin of the diagram (Fig. 4). Fe2O3
and Al2O3 contents in the Ogami and
Taihei samples also show a negative
correlation. The negative correlationsuggests that the chemical property of
Fe in river water is different from thechemical properties of Si and Al.
The Ogami and Taihei samples
have high In contents. In content of
the Ogami sample increases from 0.2
ppm at the bottom (OA-1-1) to 1.9 ppm
at the top (OB-4), with a median valueof 0.71 ppm (Fig. 3a). In content of
the Taihei sample ranges from 0.6
ppm at the bottom (A-1) to 2.5 ppm inthe middle part (A-4-1) with a medianvalue of 0.96 ppm (Fig. 3b).

Theaverage In content of both samples is 0.8 ppm with a standard deviation is 0.2 ppm. The content is 4 to
14-times higher the than average In content in the continental crust (0.056 ppm, Rudnick and Gao,
2003).
In content of the Ogami sample shows positive correlations with Pb (r = 0.98, Fig. 5c) and Fe (r =0.91, Fig. 5a). The degrees of positive correlation between In and Fe contents are different in the
distinctly banded portion and poorly banded portion in the Ogami sample.

The distinctly banded

portion has a moderate correlation (r = 0.55, Fig. 5a) between In and Fe contents, while the poorly
banded portion has a strong correlation between the contents (r = 0.98, Fig. 5a). There is a negative
correlation between In and Al contents in the Ogami sample (r = -0.13, Fig. 5b). The Taihei sample
shows a weak positive correlation between In and Fe contents (r = 0.4, Fig. 5a) and a strong positive
correlation between In and Pb contents (r = 0.64, Fig. 5c).

The degree of the positive correlation

between In and Fe contents is similar to that of the positive correlation between In and Fe contents inthe distinctly banded part of the Ogami sample. The positive correlations suggest that In tends to be
sorbed onto ferric oxide. The In content in the Taihei sample also shows a negative correlation with Alcontent (r = -0.46, Fig. 5b). The In-rich layers are characterized by high Fe and Pb contents with low Al
content.

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Fig. 3 (a) SiO2, Al2O3, Fe2O3 and In contents in Ogami sample. (b) SiO2, Al2O3, Fe2O3 and In contents in
Taihei sample.

Fig. 4 Diagram showing SiO2 and Al2O3
contents in Ogami and Taihei samples;Qz: quartz, Cr: cristobalite, Pl:plagioclase, Mont: montmorillonite,
Kaol: kaolinite, Ill: illite

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NMCC ANNUAL REPORT 20 (2013)

Fig. 5 Diagram showing relations of In with major
and trace element contents in Ogami and
Taihei samples. (a) In and Fe2O3, (b) In
and Al2O3 and (c) In and Pb.

4 Estimation of the amounts of In precipitated in Tamagawa Dam and released from Obuki
Hot Spring
Based on the average In content (0.8 ± 0.2 ppm), the thickness of Ogami and Taihei samples (0.12m), density of the sediment (1.08 g/cm3) and the area of Tamagawa Dam (6.58 km2), the amount of In
precipitated in the dam after construction of Tamagawa Dam in 1990 was estimated by the following
equation:
M = S x H x x C = 512 kg,
where M is the amount of In in Tamagawa Dam, S is the area of Tamagawa Dam, H is thickness of thesample, C is In content in sediment samples and  is density of the sediment. The amount of In in
Tamagawa Dam is estimated to have been approximately 512 kg during the past 22 years.
The amount of In released from Obuki Hot Spring was also estimated. Based on the discharge
rate (9000 l/min) and In content (0.57 ppb) of Obuki thermal water (Ogawa et al., 2012), the amount of In
that was released from the hot spring in one year was estimated by the following equation:
m = R x T x C,

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NMCC ANNUAL REPORT 20 (2013)

where m is amount of In released from Obuki Hot Spring, R is flow rate, T is time and C is concentrationof In in the thermal water from Obuki Hot Spring. The amount of In that has been released from Obuki
Hot Spring in the past 22 years is estimated as follows:m = 9000 x 60 x 24 x 365 x 22 x 0.57x 10-9 = 528 kg.
The amount of In that has been released from Obuki Hot Spring during the past 22 years is estimated to
be 528 kg.

This estimation suggests that most of the In released from Obuki Hot Spring was

precipitated in Tamagawa Dam over the 22-year period.

5 Summary
The sediment of Tamagawa Dam consists of a succession of about 10 to 12-cm-thick layers ofmetal-rich sediments. The light brownish layers are characterized by higher contents of Al and Si,
while dark reddish-brown layers are characterized by higher contents of Fe, In and Pb with lower
content of Al. In derived from Obuki Hot Spring has been mainly precipitated in Tamagawa Dam, theamounts of which has been more than 500 kg over the past 22 years.
References
Ogawa Y., Ishiyama D., Shikazono N., Iwane K., Kajiwara M. and Tsuchiya N. (2012) The role of hydrous
ferric oxide precipitation in the fractionation of arsenic, gallium, and indium during theneutralization of acidic hot spring water by river water in the Tama River watershed, Japan.
Geochimica et Cosmochimica Acta, pp. 367-383. Elsevier, Oxford.
Rudnick R.L. and Gao S. (2003) Composition of the continental crust. In The Crust, Treatise on
Geochemistry (ed. R. L. Rudnick), pp. 1-64. vol. 3. Elsevier-Pergamon, Oxford.
Satoh H., Ishiyama D., Mizuta T., and Ishikawa Y. (1999) Rare earth element analysis of rock thermal
water samples by inductively coupled plasma mass spectrometry (ICPMS). Scientific andTechnical Reports Faculty of Engineering and Resource Geology, Akita University, Japan, 20, 8p.
Satoh H., Ishiyama D., Mizuta T., Matsubaya O., and Murakami F. (2010) Geochemical characteristics ofthermal waters and precipitates in Tamagawa Hot Spring area, Akita, Japan. Shigen Chisitsu
60(1), 15-24 (in Japanese with English abstract).
Sera K., and Yanagisawa T. (1992) Bio-PIXE at the Takizawa facility (Bio-PIXE with a baby cyclotron).
Jour. PIXE, 2, pp. 325-330.
Yoshike, Y. (1993) Variation in Chemical Composition of the Tamagawa Hot Spring, Akita Prefecture(1912-1991)-Obuki Spring. J. Hot Spring Sci., v. 43, 56-67 (in Japanese with English abstract).

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