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Local Coordination of Zn and Fe in Glasses Containing Electric Arc Furnace Dust:
a NEXAFS Study
F. Pinakidou, M. Katsikini, A. Mavromati, G. Kaimakamis, Th. Kehagias and E.C. Paloura *
Aristotle University of Thessaloniki, School of Physics, 54124 Thessaloniki, Greece.
*
paloura@auth.gr
1. Introduction
Electric arc furnace dust (EAFD), which is one of the largest solid waste streams produced by steel mills, contains
mainly heavy metals and thus is considered as a toxic waste. Recycling of the valuable metals (Fe, Zn and Pb), which
reduces the disposal problems and results in resource conservation, can recover only a portion of the heavy metals from the
EAFD. Vitrification, leading to the formation of vitreous or glass-ceramic materials, is a promising process to stabilize
metallic Zn and Fe and hence permits the safe disposal of the EAFD [1]. Therefore it is of great importance to study the
bonding geometry of both Fe and Zn in vitrified EAFD-rich industrial wastes, since the structural integrity of the glass matrix
depends strongly on the type of polyhedra that Fe and Zn form.
2. Experimental Details
The studied samples are vitrified products of EAFD (which mainly consists of ZnO
and ferric oxides (ZnFe 2 O 4 )) and are produced by co-melting of the EAFD with SiO 2 ,
Na 2 O and CaO at 1400°C for 2h, followed by quenching. The EAFD concentration
ranges from 10 to 55 wt%, while the SiO 2 concentration is equal to 55 wt% in all
studied samples. The Fe-K and Zn-K-EXAFS measurements were conducted at the
synchrotron radiation facility BESSY in Berlin using the KMC2 beamline. The spectra
were recorded in the fluorescence yield mode using a Si-PIN photodiode. The spectra
from two reference samples, powder hematite (Fe 2 O 3 ) and magnetite (Fe 3 O 4 ), were
recorded in the transmission mode using ionization chambers.
3. Results and discussion
The Fe-K NEXAFS spectra of the studied samples are shown in Fig. 1(a). The
characteristic pre-edge peak is present in the spectra of all samples indicating that the
polyhedron around Fe is either a tetrahedron or an asymmetric octahedron. The preedge
absorption is attributed to 1s→3d transitions with an electric dipole or quadruple
character [2]. The quadruple character of the transition is pronounced in a
centrosymmetric environment while the dipole in non-centrosymmetric. However,
since quadrupole transitions are 20-100 times weaker than the dipole [2], the existence
of higher distortion leads to higher intensity of the pre-edge peak. Hence, the presence
of the pre-edge peak is a fingerprint of units lacking inversion center while its intensity
relates to the bonding environment of Fe. The Fe-K-NEXAFS spectra were fitted using
a sigmoidal (Boltzmann function) to simulate the absorption edge (E abs ) and Lorentz or
Voigt functions to simulate the pre-edge peak. In order to isolate the pre-edge region,
and thus reveal the characteristics of the pre-edge peak more clearly, the sigmoidal
function was subtracted from the Fe-K-NEXAFS spectra. The resulting pre-edge peaks
are shown in Fig. 2(a) while the results of the Fe-K-NEXAFS analysis are listed in
Table 1.
As mentioned above, the differences in the shape of the pre-edge peak indicate
changes in the bonding environment of Fe. The Fe-K-NEXAFS analysis reveals that
the differences in the pre-peak among the studied glasses and reference compounds are
quite significant and thus a different number of functions, centered at different energies,
is necessary to fit the pre-edge region. More specifically, as shown in Table 1, the preedge
peak of Fe 2 O 3 was fitted using functions positioned at 7113.1 and 7114.2 eV and
7116.5 eV. The first two correspond to Fe +3 in octahedral sites while the third one is
attributed to clustering of Fe [2] and its contribution will be ignored. In the spectra of
Fe 3 O 4 , the following three functions were used for the simulation of the pre-edge peak:
the one at 7111.1 eV corresponds to octahedrally coordinated Fe +2 , the second one at
7112.7 eV corr3esponds to tetrahedrally coordinated Fe +3 while the third one at 7114.6
eV is assigned to octahedrally coordinated Fe +3 . Furthermore, the total area under the
pre-edge peak is significantly different between the two reference samples. The larger
area in magnetite (0.63±0.03 a.u.) compared to hematite (0.43±0.02 a.u.) designates the
different environment of Fe: Fe ions in tetrahedral sites (non-symmetric) in Fe 3 O 4 leads
to an increase of the area while in Fe 2 O 3 , Fe occupies octahedral sites, leading to a
broader and of lower intensity (smaller area) pre-edge peak.
The differences in the shape of the pre-edge peak, which indicate coordination
changes of the Fe ion, are also detected in the spectra of the studied glasses. The
number of functions needed to fit the pre-edge peak is determined by the symmetry of
Intensity (arb. units)
Intensity (arb. units)
4
2
Fe-K edge
Fe 3
O 4
Fe 2
O 3
10 wt%
EAFD
15 wt%
EAFD
20 wt%
EAFD
25 wt%
EAFD
30 wt%
EAFD
(a)
0
7080 7100 7120 7140 7160
3
2
1
10 wt%
EAFD
15 wt%
EAFD
20 wt%
EAFD
25 wt%
EAFD
E (eV)
Zn-K edge
30 wt%
EAFD
(b)
0
9620 9640 9660 9680 9700
E (eV)
Figure 1: (a) The Fe-K NEXAFS
spectra of the studied glasses and
reference Fe 2 O 3 and Fe 3 O 4 and (b)
The respective Zn-K NEXAFS
spectra of all studied samples.
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