XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1359
adsorbate-adsorbate relationship (F. Ambroz et al 2018). As
shown in the figure, the curve rises slowly at relative pres-
sure between 0.0 to 0.8 without any inflection point due to
weak interaction between the adsorbent and the adsorbate.
At relative pressure range between 0.8 and 1.0, the curve
rises sharply as a result of capillary condensation process.
The high amount of nitrogen adsorbed indictaes that the
biochar sample before adsorption of rare earth elements has
lots of pore structure on its surface. At this level, adsorption
is taking place on mesopores through multilayer adsorp-
tion. As shown in the Table 3, the BET measurement of
the specific surface area of the sample was 5.96 m2/mg,
pore width was 3.51nm, and pore volume was 0.0088nm3
respectively.
Figure 8b shows the N2 adsorption-desorption BET
isotherm curves of the biochar sample after adsorption of
rare earth elements from aqueous solutions aided by reso-
nant vibratory mixing. From the figure, it is observed that
the pore structure is complex since the isotherm curve does
not follow any of the six adsorption isotherm curves based
on IUPAC’s classification. The hysteresis loop in the iso-
therm curve for this sample is highly separated signifying
that rare earth elements already adsorbed to the surfaces of
the sample remarkably changed the surface structure and
there are limited amount of pore spaces on the surfaces.
Since the the curves are not going all the way down as pres-
sure decreases, it is assumed that the rare earth elements
already adsorbed on the surfaces created polarity and allow-
ing bond-specific reactions between nitrogen gas and the
suface functional groups attached to rare earth elements.
For this sample, the specific surface area was 5.02 m2/g, pore
width was 2.94nm, and the pore volume was 0.0047nm3
respectively. These values are less than the values from the
previous sample before adsorption based on the data in
table 4. Adsorption of rare earth ions to the surface of the
biochar can be attributed to the reduction in surface area,
pore width, and pore volume.
Zeta Potential and Surface Charge Analysis
pH is the most important parameter for zeta potential and
the zeta potential values for the samples depend on their
pH. Figure 9 shows the variation of zeta potential values at
different pH for raw hemp hurds, hemp biochar after being
pyrolyzed, and the biochar after being used to adsorb rare
earth elements.
The point of zero charge (pHpzc) of the under-studied
hemp biochar are observable in Figure 9(a), indicating the
point where the biochar’s surface potential is equal to zero.
Based on the Figure 9(b), the pHpzc of hemp biochar after
being pyrolyzed was 3.25 which is significantly lower than
the raw hemp hurds sample (7.3), demonstrating that the
pyrolyzing of hemp biochar affects biochar surface chemis-
try and isoelectric point. In this sample, at pHs lower than
3.25 the zeta potential values decreased with decreasing pH
more significantly than the fresh sample, indicating that at
the pHs there is a high tendency to adsorb metal cations
Figure 8. (a) N2 Adsorption-Desorption BET Isotherm curves for biochar sample before adsorption of REEs (b) N2
Adsorption-Desorption BET Isotherm curves for biochar sample after adsorption of REEs
(a) (b)
Table 3. Results of BET analysis for all samples
Sample
Surface Area,
m2/mg
Average pore
width, nm
Pore Volume,
nm3
Biochar before
adsorption
5.96 3.51 0.0088
Biochar after
adsorption
5.02 2.94 0.0047
adsorbate-adsorbate relationship (F. Ambroz et al 2018). As
shown in the figure, the curve rises slowly at relative pres-
sure between 0.0 to 0.8 without any inflection point due to
weak interaction between the adsorbent and the adsorbate.
At relative pressure range between 0.8 and 1.0, the curve
rises sharply as a result of capillary condensation process.
The high amount of nitrogen adsorbed indictaes that the
biochar sample before adsorption of rare earth elements has
lots of pore structure on its surface. At this level, adsorption
is taking place on mesopores through multilayer adsorp-
tion. As shown in the Table 3, the BET measurement of
the specific surface area of the sample was 5.96 m2/mg,
pore width was 3.51nm, and pore volume was 0.0088nm3
respectively.
Figure 8b shows the N2 adsorption-desorption BET
isotherm curves of the biochar sample after adsorption of
rare earth elements from aqueous solutions aided by reso-
nant vibratory mixing. From the figure, it is observed that
the pore structure is complex since the isotherm curve does
not follow any of the six adsorption isotherm curves based
on IUPAC’s classification. The hysteresis loop in the iso-
therm curve for this sample is highly separated signifying
that rare earth elements already adsorbed to the surfaces of
the sample remarkably changed the surface structure and
there are limited amount of pore spaces on the surfaces.
Since the the curves are not going all the way down as pres-
sure decreases, it is assumed that the rare earth elements
already adsorbed on the surfaces created polarity and allow-
ing bond-specific reactions between nitrogen gas and the
suface functional groups attached to rare earth elements.
For this sample, the specific surface area was 5.02 m2/g, pore
width was 2.94nm, and the pore volume was 0.0047nm3
respectively. These values are less than the values from the
previous sample before adsorption based on the data in
table 4. Adsorption of rare earth ions to the surface of the
biochar can be attributed to the reduction in surface area,
pore width, and pore volume.
Zeta Potential and Surface Charge Analysis
pH is the most important parameter for zeta potential and
the zeta potential values for the samples depend on their
pH. Figure 9 shows the variation of zeta potential values at
different pH for raw hemp hurds, hemp biochar after being
pyrolyzed, and the biochar after being used to adsorb rare
earth elements.
The point of zero charge (pHpzc) of the under-studied
hemp biochar are observable in Figure 9(a), indicating the
point where the biochar’s surface potential is equal to zero.
Based on the Figure 9(b), the pHpzc of hemp biochar after
being pyrolyzed was 3.25 which is significantly lower than
the raw hemp hurds sample (7.3), demonstrating that the
pyrolyzing of hemp biochar affects biochar surface chemis-
try and isoelectric point. In this sample, at pHs lower than
3.25 the zeta potential values decreased with decreasing pH
more significantly than the fresh sample, indicating that at
the pHs there is a high tendency to adsorb metal cations
Figure 8. (a) N2 Adsorption-Desorption BET Isotherm curves for biochar sample before adsorption of REEs (b) N2
Adsorption-Desorption BET Isotherm curves for biochar sample after adsorption of REEs
(a) (b)
Table 3. Results of BET analysis for all samples
Sample
Surface Area,
m2/mg
Average pore
width, nm
Pore Volume,
nm3
Biochar before
adsorption
5.96 3.51 0.0088
Biochar after
adsorption
5.02 2.94 0.0047