XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3277
(SOC). SOC consist of microscopically thin layers that
can be simplified into three sections: the hydrogen side,
the oxygen side and the electrolyte in between. These sec-
tions have a high concentration of raw materials, including
various rare earth elements and nickel (Badgett et al. 2022,
Udomsilp et al. 2021), which are on the list of critical raw
materials in the EU (European Commission 2023) and the
US (U.S. Geological Survey 2022). O2–-conductors such
as yttrium- or scandium-stabilized zirconia (YSZ or ScSZ)
or gadolinium-doped ceria (GDC) are used as electrolytes,
cermets consisting of O2–-conductors and nickel are com-
mon on the hydrogen side, and perovskite-type materials
are typically used on the oxygen side (Udomsilp et al. 2021,
Wolf et al. 2023). For materials of the perovskite type,
LaxSr1-xCoyFe1-yO3-δ (LSCF) and LaSrxCo1-xO3-δ (LSC)
correspond to state of the art (Wolf et al. 2023).
Initial approaches to recovering these critical materials
from SOC have been proposed, with Sarner et al. (2022)
being the first to suggest a recycling strategy. In their
research, the first step is to separate the oxygen side from
the cell, as the specific elements are considered contami-
nants for further approaches. This also makes sense in terms
of material distribution, because the hydrogen side and the
electrolyte in the SOC often share materials, but the oxygen
side is different. Recycling approaches from other studies
also reflect the prioritization of the perovskite separation.
Sarner et al. (2023) used hydrometallurgical processes to
selectively separate the perovskite materials. The rest of
the cell was then comminuted and reused as a substrate
on the hydrogen side. Saffirio et al. (2022) and Yenesew et
al. (2023) removed oxygen-side perovskites by mechanical
scraping, followed by grinding and acid leaching to separate
nickel in the cells, leaving YSZ. The processes for separating
perovskites presented in these previously mentioned studies
achieve the required removal, but rely on expensive manual
labor or hydrometallurgical approaches that produce envi-
ronmentally hazardous residues.
To avoid these drawbacks, Kaiser et al. (2024) inves-
tigated ultrasonic decoating for the selective separation of
perovskites, which has already been successfully used in
battery recycling to separate the active material from the
metal foils in the electrodes (Lei et al. 2021). In their study,
Kaiser et al. (2024) used three different types of cells and
investigated decoating at different spacings between the cell
and the sonotrode and at different sonication times. They
used a magnet to fix the cell pieces oxygen side up under
the sonotrode in water. Two of the cell types showed com-
plete and selective decoating. The third cell type broke sev-
eral times due to the small thickness of the cells and could
therefore not be investigated further. The fractures did not
have a negative impact on the decoating result due to the
use of magnetic fixation, but did result in a much higher
evaluation effort. In fact, cells with a high number of breaks
appeared to have better decoating results than cells with
no or a low number of breaks under otherwise identical
conditions for the third cell type. The additional frictional
stress between the particles was seen as a possible reason for
this. One of the other cell types was also slightly broken in
some cases, but there was no difference compared to other
measurement points under the same conditions.
In order to recycle SOC, the SOEL must first be
destacked and the cells separated from the other compo-
nents, e.g., by disassembly (Al Assadi et al. 2023, Sarner et
al. 2022). Due to the very thin thickness of the cells and
sometimes being joint with other components obtained
with glass sealant (Harboe et al. 2020), cell breakage is not
unlikely at this preliminary stage (Al Assadi et al. 2023,
Frey et al. 2018, Jang et al. 2018, Sarner et al. 2022). A
drawback of ultrasonic decoating, as presented in the study
by Kaiser et al. (2024), is that the decoating is dependent
on the orientation of the cell with respect to the sonotrode.
This orientation dependency could make handling for
ultrasonic decoating more difficult if the cell breaks before
decoating.
This study examined the potential of ultrasonic decoat-
ing of crushed cells to separate perovskite materials from
the oxygen side. Successful ultrasonic decoating of cell
particles would be advantageous for handling because it
would provide independence from the alignment between
the cell and the sonotrode, meaning that the application
of ultrasonic decoating would not rely on non-destructive
disassembly of the SOC. Moreover, an effective frictional
stress between the individual cell particles could favor the
decoating process, as previously proposed by Kaiser et al.
(2024). For the investigation, a cell was coarsely crushed
and sieved. After sieving, the coarse fractions were sub-
jected to ultrasound, and the removed mass, particle size
distribution, composition of the products were determined
and discussed.
MATERIAL AND METHODS
Material
The SOC examined in this study is 10 × 10 cm in size from
CeramTec, provided by the Forschungszentrum Jülich, and
has a thickness of approximately 330 µm. The hydrogen
side consists of NiO and YSZ with a thickness of 270 µm,
the oxygen side consists of La0.58Sr0.4Co0.2Fe0.8O3-δ with a
thickness of about 40 µm, and in between is the electrolyte
of YSZ and the reaction barrier of GDC with a combined
thickness of 20 µm.
(SOC). SOC consist of microscopically thin layers that
can be simplified into three sections: the hydrogen side,
the oxygen side and the electrolyte in between. These sec-
tions have a high concentration of raw materials, including
various rare earth elements and nickel (Badgett et al. 2022,
Udomsilp et al. 2021), which are on the list of critical raw
materials in the EU (European Commission 2023) and the
US (U.S. Geological Survey 2022). O2–-conductors such
as yttrium- or scandium-stabilized zirconia (YSZ or ScSZ)
or gadolinium-doped ceria (GDC) are used as electrolytes,
cermets consisting of O2–-conductors and nickel are com-
mon on the hydrogen side, and perovskite-type materials
are typically used on the oxygen side (Udomsilp et al. 2021,
Wolf et al. 2023). For materials of the perovskite type,
LaxSr1-xCoyFe1-yO3-δ (LSCF) and LaSrxCo1-xO3-δ (LSC)
correspond to state of the art (Wolf et al. 2023).
Initial approaches to recovering these critical materials
from SOC have been proposed, with Sarner et al. (2022)
being the first to suggest a recycling strategy. In their
research, the first step is to separate the oxygen side from
the cell, as the specific elements are considered contami-
nants for further approaches. This also makes sense in terms
of material distribution, because the hydrogen side and the
electrolyte in the SOC often share materials, but the oxygen
side is different. Recycling approaches from other studies
also reflect the prioritization of the perovskite separation.
Sarner et al. (2023) used hydrometallurgical processes to
selectively separate the perovskite materials. The rest of
the cell was then comminuted and reused as a substrate
on the hydrogen side. Saffirio et al. (2022) and Yenesew et
al. (2023) removed oxygen-side perovskites by mechanical
scraping, followed by grinding and acid leaching to separate
nickel in the cells, leaving YSZ. The processes for separating
perovskites presented in these previously mentioned studies
achieve the required removal, but rely on expensive manual
labor or hydrometallurgical approaches that produce envi-
ronmentally hazardous residues.
To avoid these drawbacks, Kaiser et al. (2024) inves-
tigated ultrasonic decoating for the selective separation of
perovskites, which has already been successfully used in
battery recycling to separate the active material from the
metal foils in the electrodes (Lei et al. 2021). In their study,
Kaiser et al. (2024) used three different types of cells and
investigated decoating at different spacings between the cell
and the sonotrode and at different sonication times. They
used a magnet to fix the cell pieces oxygen side up under
the sonotrode in water. Two of the cell types showed com-
plete and selective decoating. The third cell type broke sev-
eral times due to the small thickness of the cells and could
therefore not be investigated further. The fractures did not
have a negative impact on the decoating result due to the
use of magnetic fixation, but did result in a much higher
evaluation effort. In fact, cells with a high number of breaks
appeared to have better decoating results than cells with
no or a low number of breaks under otherwise identical
conditions for the third cell type. The additional frictional
stress between the particles was seen as a possible reason for
this. One of the other cell types was also slightly broken in
some cases, but there was no difference compared to other
measurement points under the same conditions.
In order to recycle SOC, the SOEL must first be
destacked and the cells separated from the other compo-
nents, e.g., by disassembly (Al Assadi et al. 2023, Sarner et
al. 2022). Due to the very thin thickness of the cells and
sometimes being joint with other components obtained
with glass sealant (Harboe et al. 2020), cell breakage is not
unlikely at this preliminary stage (Al Assadi et al. 2023,
Frey et al. 2018, Jang et al. 2018, Sarner et al. 2022). A
drawback of ultrasonic decoating, as presented in the study
by Kaiser et al. (2024), is that the decoating is dependent
on the orientation of the cell with respect to the sonotrode.
This orientation dependency could make handling for
ultrasonic decoating more difficult if the cell breaks before
decoating.
This study examined the potential of ultrasonic decoat-
ing of crushed cells to separate perovskite materials from
the oxygen side. Successful ultrasonic decoating of cell
particles would be advantageous for handling because it
would provide independence from the alignment between
the cell and the sonotrode, meaning that the application
of ultrasonic decoating would not rely on non-destructive
disassembly of the SOC. Moreover, an effective frictional
stress between the individual cell particles could favor the
decoating process, as previously proposed by Kaiser et al.
(2024). For the investigation, a cell was coarsely crushed
and sieved. After sieving, the coarse fractions were sub-
jected to ultrasound, and the removed mass, particle size
distribution, composition of the products were determined
and discussed.
MATERIAL AND METHODS
Material
The SOC examined in this study is 10 × 10 cm in size from
CeramTec, provided by the Forschungszentrum Jülich, and
has a thickness of approximately 330 µm. The hydrogen
side consists of NiO and YSZ with a thickness of 270 µm,
the oxygen side consists of La0.58Sr0.4Co0.2Fe0.8O3-δ with a
thickness of about 40 µm, and in between is the electrolyte
of YSZ and the reaction barrier of GDC with a combined
thickness of 20 µm.