4
SEM
To understand the morphology of ground particles of
Sm-Co, SEM was used. Since this process is a solid-liquid
separation, it was important to understand the structure
available as active sites on the surface of ground Sm-Co
for adsorption with different DESs. SEM analysis was
performed before the chemical leaching of Sm-Co with
DESs to inspect any physical changes. The analysis was
performed using SEM model (TESCAN TIMA) available
at CAMP laboratory, Montana Technological University,
Butte, Montana, USA.
XRD
It was important to determine the presence of different min-
eral/ crystal phases in the Sm-Co sample. For this purpose,
XRD instrument (Rigoku Ultima IV available at CAMP
laboratory was used. The fitted range of 20.0°–90.0° was
used for the diffraction angles.
EDS
After doing a SEM analysis, EDS was performed using the
instrument model (EDAX Z4-i7+ Analyzer) at CAMP lab-
oratory. It was useful in quantifying the grade composition
of Sm-Co magnet.
ICP-OES
ICP-OES analysis was achieved using the instrument
(ThermoScientific ICAP 6000 Series) at CAMP labora-
tory. For the feed sample digestion method (magnets (EPA
Method 3050B) were used for the Sm-Co After sample
digestion, 250 milliliters (mL) volume sample was diluted
to 1000 milligrams/litre concentration in the volume of
50ml using 5% HNO3. For the leachate samples with and
without RAM, 5% HNO3 was used, and samples were
diluted by a factor of 10x.
Experiments
Preparation of DESs and Its Properties
For the preparation of DESs, the method was followed.
DESs were prepared via the heating method. Hydrogen
Bond Donor (HBD) and hydrogen bond acceptor (HBA)
were weighed and placed in 20ml glass screw cap vials.
The molar ratio of HBD and HBA was taken as 1:1 for
ChCl: Oxalic Acid, 1:2 for ChCl: Urea and ChCl: Ethylene
Glycol and 1:2 for TBAC: Ethylene Glycol respectively
23,24. This combination was heated on a hot plate at a
temperature range of 60°C to 100°C while stirred at 400
revolutions per minute (RPM) for a duration in the range
of 1 to 4 hours until it became a homogenous and transpar-
ent solution. The DESs were stored in glass bottles in the
oven at 50 °C for leaching experiments. The combinations
of DESs in Table 2 were used as a lixiviant for the chemical
leaching of Sm-Co magnets.
Chemical Leaching of Sm-Co
Leaching with sulfuric acid (H2SO4) was performed to cre-
ate a baseline for the research study as H2SO4 is commonly
used as a leaching reagent in extracting REEs. 0.2 grams
(g) of Sm-Co with a size fraction of +250μm/–425μm
was taken in a glass vial containing 10mL of concentrated
H2SO4. The vial was placed on a hotplate and leaching was
carried out for 2 hours at 90°C with a stirring speed of
500 revolutions per meter (RPM). The solid residue was
retained on Whatman filter paper no. 42 and leachate was
preserved in a sample vial for concentration analysis by
ICP-OES.
Leaching of Sm-Co was carried out with the prepared
DESs combination. Based on a solid-to-liquid ratio of 1:5,
0.2 g of sample with a size fraction of +250μm/–425μm
was taken, and 10 ml of prepared DESs was added to it. 1
mL of 5% HNO3 was added as a catalyst. For each experi-
ment, the leaching temperature range of 60°C–100°C, and
a leaching time range of 1–3.41 hours was set as per the
experimental design shown in Table 3. The stirring speed of
the magnetic plate was set to 400 RPM. After the dissolu-
tion of Sm-Co in DESs, the solution was separated using
a 200μm filter using a syringe. Part of the filtered solution
was preserved for without RAM analysis by ICP-OES and
part of the unfiltered solution was used further with RAM
experiments.
Table 2. presents four different combinations of deep eutectic solvents (DESs) based on two hydrogen bond donors (HBD),
which are choline chloride, and tetra butyl ammonium chloride. Three organic compounds, which function as hydrogen bond
acceptors (HBA): urea, ethylene glycerol, and oxalic acid were used. Based on varied mixing ratios of 1:1 and 1:2 of HBD:
HBA, four unique combinations of DESs
Organic Acid (HBD) Salt (HBA) Combination Name
Oxalic Acid Choline Chloride Oxaline
Ethylene Glycol Choline Chloride Ethaline
Urea Choline Chloride Reline
Ethylene Glycol Tetra Butyl Ammonium Chloride EG-TBAC
SEM
To understand the morphology of ground particles of
Sm-Co, SEM was used. Since this process is a solid-liquid
separation, it was important to understand the structure
available as active sites on the surface of ground Sm-Co
for adsorption with different DESs. SEM analysis was
performed before the chemical leaching of Sm-Co with
DESs to inspect any physical changes. The analysis was
performed using SEM model (TESCAN TIMA) available
at CAMP laboratory, Montana Technological University,
Butte, Montana, USA.
XRD
It was important to determine the presence of different min-
eral/ crystal phases in the Sm-Co sample. For this purpose,
XRD instrument (Rigoku Ultima IV available at CAMP
laboratory was used. The fitted range of 20.0°–90.0° was
used for the diffraction angles.
EDS
After doing a SEM analysis, EDS was performed using the
instrument model (EDAX Z4-i7+ Analyzer) at CAMP lab-
oratory. It was useful in quantifying the grade composition
of Sm-Co magnet.
ICP-OES
ICP-OES analysis was achieved using the instrument
(ThermoScientific ICAP 6000 Series) at CAMP labora-
tory. For the feed sample digestion method (magnets (EPA
Method 3050B) were used for the Sm-Co After sample
digestion, 250 milliliters (mL) volume sample was diluted
to 1000 milligrams/litre concentration in the volume of
50ml using 5% HNO3. For the leachate samples with and
without RAM, 5% HNO3 was used, and samples were
diluted by a factor of 10x.
Experiments
Preparation of DESs and Its Properties
For the preparation of DESs, the method was followed.
DESs were prepared via the heating method. Hydrogen
Bond Donor (HBD) and hydrogen bond acceptor (HBA)
were weighed and placed in 20ml glass screw cap vials.
The molar ratio of HBD and HBA was taken as 1:1 for
ChCl: Oxalic Acid, 1:2 for ChCl: Urea and ChCl: Ethylene
Glycol and 1:2 for TBAC: Ethylene Glycol respectively
23,24. This combination was heated on a hot plate at a
temperature range of 60°C to 100°C while stirred at 400
revolutions per minute (RPM) for a duration in the range
of 1 to 4 hours until it became a homogenous and transpar-
ent solution. The DESs were stored in glass bottles in the
oven at 50 °C for leaching experiments. The combinations
of DESs in Table 2 were used as a lixiviant for the chemical
leaching of Sm-Co magnets.
Chemical Leaching of Sm-Co
Leaching with sulfuric acid (H2SO4) was performed to cre-
ate a baseline for the research study as H2SO4 is commonly
used as a leaching reagent in extracting REEs. 0.2 grams
(g) of Sm-Co with a size fraction of +250μm/–425μm
was taken in a glass vial containing 10mL of concentrated
H2SO4. The vial was placed on a hotplate and leaching was
carried out for 2 hours at 90°C with a stirring speed of
500 revolutions per meter (RPM). The solid residue was
retained on Whatman filter paper no. 42 and leachate was
preserved in a sample vial for concentration analysis by
ICP-OES.
Leaching of Sm-Co was carried out with the prepared
DESs combination. Based on a solid-to-liquid ratio of 1:5,
0.2 g of sample with a size fraction of +250μm/–425μm
was taken, and 10 ml of prepared DESs was added to it. 1
mL of 5% HNO3 was added as a catalyst. For each experi-
ment, the leaching temperature range of 60°C–100°C, and
a leaching time range of 1–3.41 hours was set as per the
experimental design shown in Table 3. The stirring speed of
the magnetic plate was set to 400 RPM. After the dissolu-
tion of Sm-Co in DESs, the solution was separated using
a 200μm filter using a syringe. Part of the filtered solution
was preserved for without RAM analysis by ICP-OES and
part of the unfiltered solution was used further with RAM
experiments.
Table 2. presents four different combinations of deep eutectic solvents (DESs) based on two hydrogen bond donors (HBD),
which are choline chloride, and tetra butyl ammonium chloride. Three organic compounds, which function as hydrogen bond
acceptors (HBA): urea, ethylene glycerol, and oxalic acid were used. Based on varied mixing ratios of 1:1 and 1:2 of HBD:
HBA, four unique combinations of DESs
Organic Acid (HBD) Salt (HBA) Combination Name
Oxalic Acid Choline Chloride Oxaline
Ethylene Glycol Choline Chloride Ethaline
Urea Choline Chloride Reline
Ethylene Glycol Tetra Butyl Ammonium Chloride EG-TBAC