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Physica Scripta. Vol. T115, 933–935, 2005

Monitoring Trace Amounts of Lead and Arsenic Adsorption by X-ray
Absorption Fine Structure Combined with Fluorescence Spectrometry
Yasuo Izumi1,*, Fumitaka Kiyotaki1 , Taketoshi Minato1 , Dilshad Masih1 and Yoshimi Seida2
1 Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan
2 Institute of Research and Innovation, 1201 Takada, Kashiwa 277-0861, Japan

Received June 26, 2003; accepted in revised form November 25, 2003

pacs number: 61.10.HtAbstract
X-ray absorption ﬁne structure combined with ﬂuorescence spectrometry was used
for the speciation of trace amounts of lead and arsenic adsorbed. The Pb2+ species
were effectively adsorbed on a layered material Mg6 Fe2 (OH)16 (CO3 )·3H2 Ofrom 100 ppb–1.0 ppm test aqueous solutions. A eutectic mixture of PbCO3 andPb(OH)2 coagulated in the case of a 1.0 ppm Pb2+ solution, and in contrast,
the major species was ion-exchanged Pb2+ in the case of the adsorption fromthe 100 ppb aqueous solution. The arsenic species were effectively adsorbed onintercalated Fe-montmorillonite from 50 ppb–16 ppm test aqueous solutions. In
this concentration range, As3+ in the solution was oxidized upon adsorption. Theadsorbed structure was suggested to be [AsV (OH)2 (-OFe)2 ] both in the cases ofadsorption of As3+ and As5+ .

1. Introduction
Speciation of toxic elements, such as Cr6+ , Cu2+ , Zn2+ , As3+ ,Cd2+ , Hg2+ , and Pb2+ in the environment is important to theunderstanding of their effects to human health and to investigate
the removal and reuse methods. XAFS gives direct information forthe speciation of non-crystalline site. Higher-energy-resolution
XAFS spectra are desirable for precise speciation. To improveenergy resolution, the ﬂuorescence X-rays emitted from a toxic
element in the sample were analyzed by a high-energy-resolution
Rowland-type spectrometer. This method is free from the problems associated with photon-counting losses (SSD) or spectral
broadening effects at higher photon energies (Pb K-edge) [1].
Basic polyhydroxide compound of layered structure
Mg6 Fe2 (OH)16 (CO3 )·3H2 O (1) was found to be effective forlead(II) adsorption, especially when the ﬂow rate of lead test
solution was high [1]. Layered material was also good for arsenic(arsenite, arsenate) adsorption, especially in the case that ironmaterial was intercalated between the layers of montmorillonite.
2. Experimental Section
2.1. Samples
Standard lead(II) compounds were used as received anddiluted to 5.0 wt% of Pb by mixing with boron nitride. An
ion-exchanged standard sample was prepared from lead(II)nitrate aqueous solutions on NaY zeolite (JRC-Z-Y4.8,
Na58Al58 Si134 O384 ·240H2 O). The cation exchange ratio was85.5%. An adsorbent 1 was synthesized by adding NaOH tothe aqueous solution of MgCl2 and FeCl3 [1]. The speciﬁc BET
surface area was 110 m2 g−1 . The interlayer spacing was 7.79 Å
based on X-ray diffraction (XRD) measurements. A 1.0 ppm or100 ppb lead(II) nitrate solution was adsorbed at a ﬂow rate (spacevelocity) of 50 min−1 on adsorbent 1.
* e-mail: yizumi@chemenv.titech.ac.jp

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Standard AsIII and AsV compounds were used as received
and diluted to 2.0 wt% of As by mixing with boron nitride.
An adsorbent was prepared by the following procedure. 8.14 mlof a 0.43 M Fe(NO3 )3 solution and 9.33 ml of a 0.75 M
NaOH solution were mixed and left undisturbed in the dark
at 290 K for 24 h. 0.5 wt% of Na-montmorillonite (Kunipia F,Na1.5 Ca0.096Al5.1 Mg1.0 Fe0.33 Si12 O27.6 (OH)6.4 ) was suspended in
distilled water and the reaction mixture was added. The resultant
powder obtained was dried for 72 h at 313 K. The Fe loading was15.3 wt%. The sample is denoted as Fe-montmorillonite. 20 mlof 1–16 ppm solutions of AsIII 2 O3 or KH2AsV O4 was adsorbedon 50 mg of Fe-montmorillonite in a 30-ml tube at 290 K for
12 h. 500 mg of Fe-montmorillonite was packed and 50–200 ppb
solutions of AsIII 2 O3 were ﬂowed at a rate of between 1.4–2.1 ml min−1 . All the samples were pressed into 20 mm-diameterdisks for X-ray measurements.
2.2. X-ray Emission and Absorption Measurements
The X-ray measurements utilizing a ﬂuorescence spectrometer
were performed on the Undulator Beamline 10XU of SPring-8(Sayo). The storage ring energy was 8.0 GeV and the ring current
was 100–50 mA. A Si(111) double crystal monochromator and aRh-coated double mirror set were used. All the measurements
were performed at 290 K. The X-ray ﬂuorescence from thesample was analyzed by a Rowland-type spectrometer (R =220 mm) equipped with a Johansson-type Ge(555) crystal (50 ×50 mm2 , Crismatec) and a scintillation counter (Oken). The energy
resolution was 1.1 eV at the Cu K1 emission (8 keV) including thecontribution of the beamline [2] and 0.3 eV at the V K1 emission(5 keV) based on the peak width of emission and the pre-edge
absorption peaks [3].
The Pb L1 emission spectrum was measured for Pb2+adsorbed on compound 1 (Pb 0.12–1.0 wt%) and reference Pb
compounds with the excitation energy set at 13064.3 eV. Theﬂuorescence spectrometer was tuned to the center of the Pb L1peak and the Pb L3 -edge XAFS spectrum was measured. TheUndulator gap and the piezoelement were optimized to maximize
the X-ray beam ﬂux at each data point.
The As K1 emission spectrum was measured for arsenic
adsorbed on the Fe-montmorillonite (As 0.13–0.48 wt%) andreference As compounds with the excitation energy set at11885.0 eV. The ﬂuorescence spectrometer was tuned to thecenter of the As K1 peak and the As K-edge XAFS spectrum
was measured. Measurements for standard As samples and apart of As adsorbed onto Fe-montmorillonites were carriedout in transmission mode to evaluate the energy resolution
and signal-to-background ratio of the spectra obtained ineach mode.
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Yasuo Izumi, Fumitaka Kiyotaki, Taketoshi Minato, Dilshad Masih and Yoshimi Seida2.3. XAFS Data Analysis
Background subtraction of the raw XANES spectrum was performed by using a Victoreen parameter. The subtraction was notnecessary in the case of XANES utilizing the ﬂuorescence spectrometer. A smooth spline function was calculated in the postedge
region, and then the spectrum was normalized. An EXAFS curve
ﬁtting analysis was performed using empirical phase-shift andamplitude parameters for the Pb-O and As-O bonds extracted
from the EXAFS spectra of PbO2 and K[AsO2 (OH)2 ] andtheoretical phase-shift and amplitude parameters of the As• • •Febond generated using the ab-initio calculation code FEFF 8.2 [4]for the coordinates of AsFeO4 crystal [5].
3. Results and Discussion
3.1. Pb L1 Emission and L3 -edge Absorption Spectra
The Pb L1 emission peak appeared at 10551.5 eV for 0.12 wt%
Pb adsorbed on compound 1 from a 100 ppb Pb2+ solution. Thefull width at a half maximum (FWHM) obtained by the peak ﬁtusing a pseudo-Voigt function was 11.7 eV. The core-hole lifetime
width of Pb L3 is 5.81 eV and the energy resolution of spectrometer
was evaluated to be 10.1 eV, including the contribution of thebeamline.
Normalized Pb L3 -edge XANES spectra are depicted inFigure 1. The rising edge for standard PbII inorganic compounds
shifted by 2.8–4.3 eV toward higher energy compared to
13040.6 eV for Pb0 . The rising edge for lead (0.12–1.0 wt%)
adsorbed on compound 1 appeared within the range 13042.9–13044.2 eV (a–c), demonstrating that the adsorbed lead state
was II. The rising edge and maximum point energies forthe spectrum for 1.0 wt% Pb on compound 1 (13044.2 and
13056.3 eV, respectively; Figure 1a) prepared from 1.0 ppm test
solution resembled only that for 2PbCO3 ·Pb(OH)2 (13044.0 and
13055.5 eV, respectively; g).
The samples of 0.30 and 0.12 wt% Pb on compound 1 wereboth prepared from 100 ppb Pb2+ solution, and the two spectra(b) and (c) resembled each other. Based on the rising edge andthe maximum point energies, these two spectra (13043.0 ± 0.1 eV
and 13054.3 ± 0.7 eV, respectively) resembled only that for PbY(13043.4 and 13054.4 eV, respectively; d).

Fig. 1. Normalized Pb L3 -edge XANES spectra for Pb2+ on (1) measured
utilizing a secondary ﬂuorescence spectrometer (a–c). The Pb content was 1.0 wt%
adsorbed from 1.0 ppm Pb2+ solution (a) and Pb 0.30 (b) and 0.12 wt% (c)from 100 ppb solution. Reference XANES spectra for PbY zeolite (d), PbO (e),Pb(NO3 )2 (f), 2PbCO3 ·Pb(OH)2 (g), Pb6 O4 (OH)4 (h), and PbCO3 (i). (d)–(i) were
measured in the conventional transmission mode.
Physica Scripta T115

The comparison of post-edge peak at 13094–13097 eV andthe unresolved shoulder peak at 13049 eV supported above
assignments of lead species in Figure 1a–c. Most of the Pb2+
coagulated as a eutectic mixture of PbCO3 and Pb(OH)2 oncompound 1 in the case from a 1.0 ppm solution. The hydroxyl
groups should be derived from the buffering effect of basic surfaceof compound 1. The formation of pure PbCO3 by the reaction
with intercalated/dissolved carbonate or pure Pb6 O4 (OH)4 by thereaction with surface hydroxyl groups should be negligible. Incontrast, in the case of the 100 ppb solution, the major lead phase
was ion-exchanged Pb2+ via the surface reaction −OH + Pb2+ →−OPb+ + H+ . A shoulder peak at 13049 eV (Figure 1b and c)suggests a minor contribution from a coagulated eutectic mixtureof PbCO3 and Pb(OH)2 on compound 1. Pb L3 -edge EXAFS wasmeasured for the sample of Figure 1a. The Pb-O bond was foundat 2.4 Å and the coordination number (N) was ≈3 [6].
3.2. As K1 Emission and K-edge Absorption Spectra
The As K1 emission peak appeared at 10544.7 eV for 0.48 wt%
As adsorbed on Fe-montmorillonite from a 16 ppm test solutionof As5+ . The FWHM obtained by the peak ﬁt using a pseudoVoigt function was 5.72 eV. The total core-hole lifetime width for
As K1 is 3.08 eV and the energy resolution of the spectrometer
was evaluated to be 4.8 eV, including the contribution of beamline.
Note that this value will be an overestimation in the case that As5+and As3+ co-exist as adsorbed in the sample. The corresponding
value of energy resolution was estimated to be 1.3 eV for anarsenic metal sample.
Normalized arsenic K-edge XANES spectra are depicted inFigure 2. The maximum point energy above the edge shifts from11867.1 for the arsenic metal (a) to 11868.5 forAsIII 2 O3 (b) then to11872.1 eV for K[AsV O2 (OH)2 ] (c). The maximum point energyfor (d)–(g) was similar to the case of (c). The spectrum patternof the arsenic adsorbed from the 16 ppm arsenate solution (d)closely resembled that of K[AsO2 (OH)2 ]. Unexpectedly, spectra(e)–(g) for the samples prepared from the arsenite solution weremore similar to (c) than they were to (b). Hence, in the caseFig. 2. As K-edge XANES spectra measured at 290 K for As metal (a), As2 O3(b), KH2AsO4 (c), and As adsorbed (d–g) on Fe-montmorillonite (Fe 15.3 wt%)from test solutions of 16 ppm of KH2AsO4 (d), 16 ppm of As2 O3 (e), 200 ppb of
As2 O3 (f ), and 50 ppb of As2 O3 (g). Spectra (a)–(c) and (g) were measured intransmission mode and (d)–(f) were measured in ﬂuorescence mode utilizing asecondary ﬂuorescence spectrometer.
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Monitoring Trace Amounts of Lead and Arsenic Adsorptionof the arsenic adsorbed from arsenite solutions in the range of50 ppb–16 ppm, most of the As3+ was oxidized to As5+ uponadsorption.A minor peak for adsorbedAsIII appeared as a shoulder
feature at 11868.8–11869.8 eV in (e) and (f). Arsenic K-edge
EXAFS was measured for arsenic adsorbed from 200 ppb–16 ppm
on Fe-montmorillonite. The As-O and As• • •Fe distances were1.68 Å (N ≈ 3) and 3.22–3.25 Å (N ≈ 2), respectively. Also
based on the crystallographic structure of FeO(OH) where [FeO6 ]octahedral are connected at the edge, the mechanism of oxidative
adsorption of As may be formulated as equation 1. [AsO2 (OH)2 ]−was also suggested for spectrum d adsorbed from arsenate[9–11].

As|||(OH)3+O O
O−Fe|||→AsHOO O + H2O(1)O--Fe||

4. Conclusions
X-ray absorption ﬁne structure combined with ﬂuorescence
spectrometry was successfully applied to trace amounts of leadand arsenic adsorbed from aqueous solutions containing 50 ppb–
16 ppm of lead or arsenic. Based on Pb L3 -edge XANES, it
was found that a eutectic mixture of PbCO3 and Pb(OH)2
coagulated in the case of the 1.0 ppm Pb2+ solution, whereasthe major species was ion-exchanged Pb2+ in the case ofadsorption from 100 ppb Pb2+ solution. Both arsenate and arsenite
species were adsorbed on Fe-montmorillonite (Fe 15.3 wt%) fromC Physica Scripta 2005

50 ppb– 16 ppm solutions containing of As. In this concentration
range, As3+ in solution was oxidized to As5+ upon adsorption.
Because the As3+ is more toxic [8, 9], Fe-montmorillonite
effectively trapped trace amounts of As3+ in solution anddetoxiﬁed it.

Acknowledgments
This work was supported by a grant from the Grant-in-Aid for Encouragement ofYoung Scientists from the Ministry of Education, Culture, Sports, Science, andTechnology (1474 0401) to proceed research and a grant from Tokuyama Science
Foundation for the travel and housing at Malmo.

O−Fe||HO

HO−Fe|||

935

References
1. Izumi, Y., Kiyotaki, F., Minato, T. and Seida, Y., Anal. Chem. 74, 3819
(2002).
2. Izumi, Y., Kiyotaki, F., Nagamori, H. and Minato, T., J. Electron Spectrosc.
Relat. Phenom. 119, 193 (2001).
3. Izumi, Y. et al., Chem. Lett. 31, 1154 (2002).
4. Ankudinov, A. L., Ravel, B., Rehr, J. J. and Conradson, S. D., Phys. Rev. B
58, 7565 (1998).
5. Cheetham, A. K. et al., Nature 320, 46 (1986).
6. Izumi, Y., Kiyotaki, F. and Seida, Y., J. Phys. Chem. B 106, 1518 (2002).
7. Oyanagi, H. et al., J. Synchrotron Rad. 7, 89 (2000).
8. Nordstrom, D. K., Science 296, 2143 (2002).
9. Farquhar, M. L., Charnock, J. M., Livens, F. R. and Vaughan, D. J., Environ.
Sci. Technol. 36, 1757 (2002).
10. Waychunas, G. A., Fuller, C. C., Rea, B. A. and Davis, J. A., Geochim.
Cosmochim. Acta 60, 1765 (1996).
11. Randall, S. R., Sherman, D. M. and Ragnarsdottir, K. V., Geochim.
Cosmochim. Acta 65, 1015 (2001).

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