1356 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Adsorption Experiments for Individual Rare
Earth Elements
Adsorption experiments for individual REEs were per-
formed in batch mode. Six rare earth elements (lanthanum,
neodymium, dysprosium, holmium, praseodymium, and
terbium) stock solutions were prepared from their chloride
salts. Stock solutions of each of these REEs with concen-
trations of 200 ppm, 400 ppm, 600 ppm, 800 ppm, and
1000 ppm were prepared by dissolving known amount of
each rare earth chloride salts in deionized distilled water
based on the required concentrations. According to the
experimental design described earlier, 5 mg, 20 mg, and
35 mg of the biochar sample was measured and transferred
into WHEATON clear polystyrene plastic vials containing
10 ml of the five concentrations for each of the six rare
earth element aqueous solutions. The vials containing both
the biochar adsorbents and rare earth aqueous solutions
were inserted into a reactor and loaded into the Resonant
vibratory Mixer (RVM). The adsorption experiments were
conducted for three different mixing times of 1 minute,
13 minutes, and 25 minutes. Adsorption experiments were
also performed by intensification with stirring as a con-
ventional method. Although, no experimental design was
developed for the stirring method, the same procedure was
repeated for 25 minutes stirring time and mixing speed of
350 rpm was set with a magnetic stirrer. The purpose of the
stirring intensification adsorption experiments was to com-
pare the results with the resonant acoustic mixing experi-
ments and to validate the efficiency of resonant acoustic
mixing as a better intensification method.
Column Leaching and Adsorption Experiments for
Bear Lodge Ore Samples
A batch column leaching experiment was conducted on the
bear lodge REEs ore sample obtained from Rare Elements
Resources Limited, based on method described by Wu,
Xiaoyan, et al, (2019). The experiment was carried out by
weighing 300g of the ore and transferred into a cylindrical
leaching column made of glass which is 75 mm in inner
diameter and 432 mm in length. Two “602H” Whatman
filter paper circles with diameters of 125 mm were reduced
into smaller circular size of 75.3 mm to fit into the cylindri-
cal leaching column. One of the filter papers was inserted
to the bottom of the glass column before transferring the
rare earth ore sample, while the second filter paper was care-
fully placed on the packed ore sample to prevent smaller ore
particles from getting into the leachate and to provide for
balanced lixiviant contact. A 250 ml amount of 0.3M con-
centration of oxalic acid was prepared by dissolving known
amount of oxalic acid crystals in deionized water. The bea-
ker containing the oxalic acid was then placed on a Cole-
Parmer IKA RETcontrol-visc stirring hot plate and heated
for 1 hour at a constant temperature of 100°C while being
stirred at 400 rpm speed. A Cole-Parmer MasterFlex L/S
peristaltic pump was used was used to pass the oxalic acid
into the leaching column from the top with a flexible pipe
at a constant flow rate of 6.5 ml/minute. The experiments
were conducted three times to produce rare earth leachates
with pH 1, 4, and 7 respectively.
RESULTS AND DISCUSSION
Adsorbent Characterization
Surface Structure and Morphology
The surface morphology of the biochar before and after
adsorption were displayed in Figures 5(a), (b), (c), (d)
and 6(e), (f), (g), (h) respectively. The SEM images before
adsorption in Figure 4(a), (b), and (c) reveals well-struc-
tured honeycomb features with orderly arranged pore sizes.
One end of the biochar particle structure shows a smooth
surface while the other end reveals partially rough surface.
Figure 3(d) is a higher magnification of the biochar’s pore
structure displaying a mesopore size and some ultra-micro-
pores along the walls.
The surface of the biochar sample after adsorption
shows rough facets exposing more of the spongy form
containing a lot of smaller pores (ultra-micropores) in
Figure 6(e), (f). This is assumed to be as a result of the
low shear vibratory action of the resonant acoustic mixer
disintegrating the biochar particles into fragments. Figures
6(g), (h) reveals more of the work done by the resonant
acoustic mixer as the structures show the split ends of the
biochar particle.
Table 2. Experimental Design showing number of runs
Std Runs Time (X1)
Intensity
(X2)
Biochar Mass
(X3)
9 1 13 40 20
4 2 25 70 5
1 3 1 10 5
11 4 13 40 20
2 5 25 10 5
5 6 1 10 35
6 7 25 10 35
3 8 1 70 5
7 9 1 70 35
8 10 25 70 35
10 11 13 40 20
Adsorption Experiments for Individual Rare
Earth Elements
Adsorption experiments for individual REEs were per-
formed in batch mode. Six rare earth elements (lanthanum,
neodymium, dysprosium, holmium, praseodymium, and
terbium) stock solutions were prepared from their chloride
salts. Stock solutions of each of these REEs with concen-
trations of 200 ppm, 400 ppm, 600 ppm, 800 ppm, and
1000 ppm were prepared by dissolving known amount of
each rare earth chloride salts in deionized distilled water
based on the required concentrations. According to the
experimental design described earlier, 5 mg, 20 mg, and
35 mg of the biochar sample was measured and transferred
into WHEATON clear polystyrene plastic vials containing
10 ml of the five concentrations for each of the six rare
earth element aqueous solutions. The vials containing both
the biochar adsorbents and rare earth aqueous solutions
were inserted into a reactor and loaded into the Resonant
vibratory Mixer (RVM). The adsorption experiments were
conducted for three different mixing times of 1 minute,
13 minutes, and 25 minutes. Adsorption experiments were
also performed by intensification with stirring as a con-
ventional method. Although, no experimental design was
developed for the stirring method, the same procedure was
repeated for 25 minutes stirring time and mixing speed of
350 rpm was set with a magnetic stirrer. The purpose of the
stirring intensification adsorption experiments was to com-
pare the results with the resonant acoustic mixing experi-
ments and to validate the efficiency of resonant acoustic
mixing as a better intensification method.
Column Leaching and Adsorption Experiments for
Bear Lodge Ore Samples
A batch column leaching experiment was conducted on the
bear lodge REEs ore sample obtained from Rare Elements
Resources Limited, based on method described by Wu,
Xiaoyan, et al, (2019). The experiment was carried out by
weighing 300g of the ore and transferred into a cylindrical
leaching column made of glass which is 75 mm in inner
diameter and 432 mm in length. Two “602H” Whatman
filter paper circles with diameters of 125 mm were reduced
into smaller circular size of 75.3 mm to fit into the cylindri-
cal leaching column. One of the filter papers was inserted
to the bottom of the glass column before transferring the
rare earth ore sample, while the second filter paper was care-
fully placed on the packed ore sample to prevent smaller ore
particles from getting into the leachate and to provide for
balanced lixiviant contact. A 250 ml amount of 0.3M con-
centration of oxalic acid was prepared by dissolving known
amount of oxalic acid crystals in deionized water. The bea-
ker containing the oxalic acid was then placed on a Cole-
Parmer IKA RETcontrol-visc stirring hot plate and heated
for 1 hour at a constant temperature of 100°C while being
stirred at 400 rpm speed. A Cole-Parmer MasterFlex L/S
peristaltic pump was used was used to pass the oxalic acid
into the leaching column from the top with a flexible pipe
at a constant flow rate of 6.5 ml/minute. The experiments
were conducted three times to produce rare earth leachates
with pH 1, 4, and 7 respectively.
RESULTS AND DISCUSSION
Adsorbent Characterization
Surface Structure and Morphology
The surface morphology of the biochar before and after
adsorption were displayed in Figures 5(a), (b), (c), (d)
and 6(e), (f), (g), (h) respectively. The SEM images before
adsorption in Figure 4(a), (b), and (c) reveals well-struc-
tured honeycomb features with orderly arranged pore sizes.
One end of the biochar particle structure shows a smooth
surface while the other end reveals partially rough surface.
Figure 3(d) is a higher magnification of the biochar’s pore
structure displaying a mesopore size and some ultra-micro-
pores along the walls.
The surface of the biochar sample after adsorption
shows rough facets exposing more of the spongy form
containing a lot of smaller pores (ultra-micropores) in
Figure 6(e), (f). This is assumed to be as a result of the
low shear vibratory action of the resonant acoustic mixer
disintegrating the biochar particles into fragments. Figures
6(g), (h) reveals more of the work done by the resonant
acoustic mixer as the structures show the split ends of the
biochar particle.
Table 2. Experimental Design showing number of runs
Std Runs Time (X1)
Intensity
(X2)
Biochar Mass
(X3)
9 1 13 40 20
4 2 25 70 5
1 3 1 10 5
11 4 13 40 20
2 5 25 10 5
5 6 1 10 35
6 7 25 10 35
3 8 1 70 5
7 9 1 70 35
8 10 25 70 35
10 11 13 40 20