XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3257
content, the behavior of the particles difference depends on
the pH of solution. At pH 4, the amount of attached par-
ticle is almost the same with 20 %of Nafion. The bubble
coverage angle decreases to 90° representing less hydro-
phobic characteristics. However, as explained in previous
study, as carbon black aggregates, its weight increases and
it cannot be attached on the air bubble surface, so the angle
tends to be measured small despite its low wettability (Ahn
&Rudolph, 2024). At pH 10, with increasing amounts of
ionomer, the amount of particles attached to the bubbles
decreases and then increases again. However, the confidence
interval (90 %)also shows a relatively large value, so it is
difficult to see this as a significant difference. Obviously,
for both pH conditions, the coverage angles of the particles
with ionomers are smaller than those without.
Samples of TiO2 have smaller coverage angles com-
pared to those of carbon black. At pH 4, TiO2 is positively
charged but shows low coverage angles except for the sam-
ple containing 20 %Nafion. This behavior can be inter-
preted by weaker Van der Waals attractive force between
oppositely charged particles than hydrophobic interac-
tion. Inherently TiO2 is hydrophilic, fewer particles can be
attached on the air droplet. The sample with 20 %Nafion
shows the largest coverage angle, which is greater than
200°. As described in the previous section, the structural
alignment of the ionomer may influence to the hydropho-
bicity of the particle. Since the hydrophobic ionomer back-
bone is oriented to the outer side of the particle resulting
lower wettability of TiO2. An excessive amount of ionomer
will lead to ionomer bilayer formation. Hence, on the outer
side of the TiO2 particle surface the hydrophilic sulfonic
acid groups interacts more strongly with the surrounding
water molecules. However, particle suspension at pH 10 is
extremely stable for a long-term thereby settling down of
the particle is almost impossible because the images can be
taken only when all particles have settled and the suspen-
sion is transparent. Measuring a bubble coverage angle is
not possible except with the sample of 40 %Nafion con-
tent. The result shows a relatively small coverage angle, not
much different from that at pH 4 conditions. Likewise,
dominant TiO2 particles failed to be attracted to the hydro-
phobic air bubbles.
Liquid-Liquid Phase Separation
Fine particle mixtures with contrast in their wettability
characteristics can be separated by two immiscible liquids.
Carbon black is inherently hydrophobic and most of the
particles can be found as stabilized droplets, which are
called Pickering emulsions, accumulated at the water and
the oil interface. The emulsion phase belongs to the organic
phase by our definition but it is also separately depicted in
Figure 5. Approximately 98 %of samples without ionomer
transferred to the organic phases. With increasing Nafion
content, the amount of particles remaining in the aque-
ous phase increases from 1.3 %to 4 %but still dominant
particles can be found in the organic phase. Except for the
mass loss during the experiment, the negligible distinction
of mass percentage for each phase is observed. With the
highest Nafion content, more particles overcome the sur-
face tension and they are able to pass the interface. The
interfacial tension between the ionomer containing sam-
ple particle and cyclohexane is greater than the sum of the
interfacial tension between water and both particle and oil
phase. A study from Andersen and Grahl-Madsen (2016)
introduced the correlation between the ionomer loading
and electrode performance of PEM fuel cell. The inves-
tigated catalysts contained Pt black supported on carbon
black with different ratios of ionomer and they confirmed
that the samples containing below 30 %of the ionomer
were not able to be fully covered by the ionomer layer.
Furthermore, high ionomer content (40 %and 50 %by
weight) could lead formation of ionomer aggregations. The
degree of ionomer coverage may influence the interactions
between the organic phase and catalyst particles.
Samples of TiO2 particles without ionomer mostly can
be found in the aqueous phase 80.8 ± 0.2 %.The particle
behavior is influenced by the Nafion content because fewer
particles are able to remain in the aqueous phase, 37.3 ±
0.9 %and 42.7 ± 0.1 %respectively. Consistent with the
air bubble coverage angle measurements, particles contain-
ing 20 %Nafion appear to be more hydrophobic. Almost
50 %percentage of the particles transferred to the inter-
face of oil and water. Increasing the ionomer content to
40 %,more particles are transferred to the organic phase.
The excessive amount of ionomer could lead the compos-
ites to adopt the bulk-like behavior which brings about the
overcome of interface resistance. Compared to the previous
bubble coverage angle measurement results, this could be
explained by the hypothesis that it was more difficult to
attach to the air bubbles because of the larger particle size.
CONCLUSIONS
This study investigated the impact of ionomer with differ-
ent contents on the mechanical separation processes for
recycling PEM water electrolyzers. Based on the previous
study, the wettability of representing catalyst particles is
confirmed that anode materials are hydrophilic and cathode
materials are hydrophobic. Due to the complex structure of
the ionomer, it may influence to the surface properties of
the particle so that the investigated separation process may
content, the behavior of the particles difference depends on
the pH of solution. At pH 4, the amount of attached par-
ticle is almost the same with 20 %of Nafion. The bubble
coverage angle decreases to 90° representing less hydro-
phobic characteristics. However, as explained in previous
study, as carbon black aggregates, its weight increases and
it cannot be attached on the air bubble surface, so the angle
tends to be measured small despite its low wettability (Ahn
&Rudolph, 2024). At pH 10, with increasing amounts of
ionomer, the amount of particles attached to the bubbles
decreases and then increases again. However, the confidence
interval (90 %)also shows a relatively large value, so it is
difficult to see this as a significant difference. Obviously,
for both pH conditions, the coverage angles of the particles
with ionomers are smaller than those without.
Samples of TiO2 have smaller coverage angles com-
pared to those of carbon black. At pH 4, TiO2 is positively
charged but shows low coverage angles except for the sam-
ple containing 20 %Nafion. This behavior can be inter-
preted by weaker Van der Waals attractive force between
oppositely charged particles than hydrophobic interac-
tion. Inherently TiO2 is hydrophilic, fewer particles can be
attached on the air droplet. The sample with 20 %Nafion
shows the largest coverage angle, which is greater than
200°. As described in the previous section, the structural
alignment of the ionomer may influence to the hydropho-
bicity of the particle. Since the hydrophobic ionomer back-
bone is oriented to the outer side of the particle resulting
lower wettability of TiO2. An excessive amount of ionomer
will lead to ionomer bilayer formation. Hence, on the outer
side of the TiO2 particle surface the hydrophilic sulfonic
acid groups interacts more strongly with the surrounding
water molecules. However, particle suspension at pH 10 is
extremely stable for a long-term thereby settling down of
the particle is almost impossible because the images can be
taken only when all particles have settled and the suspen-
sion is transparent. Measuring a bubble coverage angle is
not possible except with the sample of 40 %Nafion con-
tent. The result shows a relatively small coverage angle, not
much different from that at pH 4 conditions. Likewise,
dominant TiO2 particles failed to be attracted to the hydro-
phobic air bubbles.
Liquid-Liquid Phase Separation
Fine particle mixtures with contrast in their wettability
characteristics can be separated by two immiscible liquids.
Carbon black is inherently hydrophobic and most of the
particles can be found as stabilized droplets, which are
called Pickering emulsions, accumulated at the water and
the oil interface. The emulsion phase belongs to the organic
phase by our definition but it is also separately depicted in
Figure 5. Approximately 98 %of samples without ionomer
transferred to the organic phases. With increasing Nafion
content, the amount of particles remaining in the aque-
ous phase increases from 1.3 %to 4 %but still dominant
particles can be found in the organic phase. Except for the
mass loss during the experiment, the negligible distinction
of mass percentage for each phase is observed. With the
highest Nafion content, more particles overcome the sur-
face tension and they are able to pass the interface. The
interfacial tension between the ionomer containing sam-
ple particle and cyclohexane is greater than the sum of the
interfacial tension between water and both particle and oil
phase. A study from Andersen and Grahl-Madsen (2016)
introduced the correlation between the ionomer loading
and electrode performance of PEM fuel cell. The inves-
tigated catalysts contained Pt black supported on carbon
black with different ratios of ionomer and they confirmed
that the samples containing below 30 %of the ionomer
were not able to be fully covered by the ionomer layer.
Furthermore, high ionomer content (40 %and 50 %by
weight) could lead formation of ionomer aggregations. The
degree of ionomer coverage may influence the interactions
between the organic phase and catalyst particles.
Samples of TiO2 particles without ionomer mostly can
be found in the aqueous phase 80.8 ± 0.2 %.The particle
behavior is influenced by the Nafion content because fewer
particles are able to remain in the aqueous phase, 37.3 ±
0.9 %and 42.7 ± 0.1 %respectively. Consistent with the
air bubble coverage angle measurements, particles contain-
ing 20 %Nafion appear to be more hydrophobic. Almost
50 %percentage of the particles transferred to the inter-
face of oil and water. Increasing the ionomer content to
40 %,more particles are transferred to the organic phase.
The excessive amount of ionomer could lead the compos-
ites to adopt the bulk-like behavior which brings about the
overcome of interface resistance. Compared to the previous
bubble coverage angle measurement results, this could be
explained by the hypothesis that it was more difficult to
attach to the air bubbles because of the larger particle size.
CONCLUSIONS
This study investigated the impact of ionomer with differ-
ent contents on the mechanical separation processes for
recycling PEM water electrolyzers. Based on the previous
study, the wettability of representing catalyst particles is
confirmed that anode materials are hydrophilic and cathode
materials are hydrophobic. Due to the complex structure of
the ionomer, it may influence to the surface properties of
the particle so that the investigated separation process may