Photon Factory Activity Report 2014 #32 (2015) B

BL-9C/2014G066

Speciation of chromium in contaminated soil from dumped slag in Tokyo
Mayumi Hori,* Katsumi Shozugawa and Motoyuki Matsuo
Graduate School of Arts and Sciences, The University of Tokyo
3-8-1, Komaba, Meguro-ku, Tokyo 153-8902, Japan
1 Introduction
Chemical states of elements in sediment or soil haveoften been used as an index to evaluate redox condition.
In addition, the mobility of elements changes by its
oxidation states. For instance, Cr(VI) species have highmobility because of its presence in highly solubleoxyanion: CrO42-, HCrO4-, Cr2O72-. In contrast, Cr(III)rarely migrates in the environment because it precipitates
as Cr(OH)3.
Highly Cr(VI) contaminants have often found ingroundwater and soils around the chromium slag
dumpling site in Edogawa-ward and Koto-ward, Tokyo,
although the government applied a reduction to Cr(III) byFeSO4 treatment. We investigated Cr(VI) pollution inthese areas and found that heavy rain and snowfall cause
elution of Cr(VI) from the slag [1]. However, thechemical species of eluted Cr(VI) is not still understood.
Further, the valence of Cr should be measured directly
because liquid phase experiments such as extraction may
cause some chemical changes. Therefore, we directlyanalyzed the Cr(VI) contaminants by using XAFS toconfirm the chemical species of Cr(VI) contaminants
flowing out at present.

chromate and dichromate reference samples (Figure).
This result indicates that Cr(VI) is mainly present aschromate or dichromate compound which is an oxyanion(CrO42-, Cr2O72-). Furthermore, it is considered that theorigin of Cr(VI) contaminant is the chromium slag. In
case of heavy rain, Cr(VI) in the slag is eluted byrainwater because sodium chromate is soluble in water.
As a result, eluted Cr(VI) solution flows out and Cr(VI)pollution occurs around the Park. In addition, wemeasured Fe K-edge XANES spectrum of contaminatedsoil sample, confirming that Cr(III) in the sample ispresent as FexCr1-x(OH)3. It is considered that eluted
Cr(VI) is reduced to Cr(III) by Fe(II), and it precipitates
as FexCr1-x(OH)3. These findings would be helpful forunderstand how Cr(VI) is released from the slag in thisarea.

2 ExperimentContaminated soil sample was collected from catchbasin around Ojima-Komatsugawa Park, which lies in
Edogawa-ku and Koto-ku. After sampling, the collectedsoil sample was packed into polyethylene bag for XAFSanalysis.
Cr K-edge XANES spectra and Fe K-edge XANES
spectra were measured in the fluorescence mode using aLytle type detector at the BL-9C equipped with a double
crystal monochromator of Si(111). The measurements
were carried out at room temperature. The spectra weretreated by the REX2000 program (Rigaku Corporation).
3 Results and Discussion
Figure shows the normalized Cr K-edge XANES
spectra of the Cr(VI) reference materials and thecontaminated soil sample. As shown in Figure, pre-edge
peak at 5992 eV, which is characteristic of Cr(VI),appeared for all samples, indicating that the soil sample
present in the hexavalent oxidation states. The chromiumslag under the ground at Ojima-Komatsugawa Park
included sodium chromate [2]. In order to confirm thechemical species of Cr(VI) in contaminated soil, we
compared the spectrum of the sample with the referencematerials. The feature at 6000 eV around the pre-edge
peak of the sample was mostly similar to those ofFigure Cr K-edge XANES spectra of the Cr(VI)reference materials (CrO3, K2CrO4, K2Cr2O7, Na2CrO4,Na2Cr2O7) and the contaminated soil sample in catchbasin.
References[1] M. Hori et al., Journal of Material Cycles and Waste
Management, 17(1), 201 (2015).
[2] T Asami, J Sci Soil Manure Jpn, 44, 223 (1973).
* cmayumi@mail.ecc.u-tokyo.ac.jp