XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1671
REFERENCES
Antuñano, N., Cambra, J.F., Arias, P.L, 2019.
Hydrometallurgical processes for Waelz oxide valorisa-
tion—An overview: Process Saf. Environ. Prot., 129,
308–20.
Anon, 1989. Recovery of zinc from EAF dust by the Waelz
process. Steel Times 217, 194–195.
Binnemans, K., Jones, P.T., Fernández, Á.M., Torres, V.M.,
2020. Hydrometallurgical Processes for the Recovery
of Metals from Steel Industry By-Products: A Critical
Review. J. Sustain. Metall., 6, 505–40.
Chairaksa, R., Inoue, Y., Umeda, N., Itoh, S., Nagasaka,
T., 2015. New pyrometallurgical process of EAF dust
treatment with CaO addition, Int. Journ. Min. Metall.
Mater. 22, 788.
Chairaksa, R., Maruyama, K., Miki, T., Nagasaka, T., 2016.
Hydrometallurgy 159, 120–125.
Da Silva, M.C., Bernardes, A.M., Bergmann, C.P., Tenório,
J.A.S., Espinosa, D.C.R., 2008. Characterisation of
electric arc furnace dust generated during plain car-
bon steel production, Ironmaking &Steelmaking 35,
315–320.
De Buzin, P.J.W.K., Heck, N.C., Vilela, A.C.F., 2017. EAF
dust: An overview on the influences of physical, chemi-
cal, and mineral features on its recycling and waste
incorporation routes, J. Mat. Res. Tech. 6, 194–202.
European Agency for Safety and Health at Work, 2006.
Regulation (EC) no. (1907/2006)—Registration,
Evaluation, Authorisation and Restriction of Chemicals
(REACH). https://osha.europa.eu/en/legislation
/directives/regulation-ec-no-1907-2006-of-the
-european-parliament-and-of-the-council.
Gamutan, J., Koide, S., Sasaki, Y., Nagasaka, T., 2024.
Selective dissolution and kinetics of leaching zinc from
lime treated electric arc furnace dust by alkaline media.
Journal of Environmental Chemical Engineering 12,
111789.
Han, Z., Holappa, L., 2003. Bubble bursting phenomenon
in Gas/Metal/Slag systems. Metall. Mater. Trans. B 34,
525–532.
Havlik, T., Souza, B.V., Bernardes, A.M., Schneider,
I.A.H., Miskufova, A., 2006. Hydrometallurgical pro-
cessing of carbon steel EAF dust. J. Hazard. Mater.,
135, 311–318.
International Energy Agency, 2020. Iron and Steel
Technology Roadmap Towards More Sustainable
Steelmaking, 103. Available at https://www.iea.org
/reports/iron-and-steel-technology-roadmap
Itoh, S., Tsubone, A., Matsubae, K., Nakajima, K.,
Nagasaka, T., 2008. New EAF Dust Treatment Process
with the Aid of Strong Magnetic Field, ISIJ Int. 48,
1339–1344.
Langová, Š. and Matýsek, D., 2010. Zinc recovery from
steel-making wastes by acid pressure leaching and hema-
tite precipitation. Hydrometallurgy, 101, 171–173.
Levenspiel, O., 1999. Chemical Reaction Engineering, 3rd
ed. New York, USA: John Wiley &Sons.
Nakajima, K., Matsubae-Yokoyama, K., Nakamura, S.,
Itoh, S., Nagasaka, T., 2008. Substance flow analysis
of zinc associated with iron and steel cycle in Japan,
and environmental assessment of EAF dust recycling
process, ISIJ Int. 48, 1478–1483.
Nakayama, T., Taniishi, H., 2011. Dust recycling technol-
ogy for electric arc furnace using RHF. Nippon. Steel
Eng. Tech. Rev. 2, 25–29.
Nakayama, M., 2012. EAF dust treatment for high metal
recovery. SEAISI Q. J. 41, 22–26.
Nagasaka, T., Itoh, S., Yokoyama, K., Nakajima, K.,
Japanese Patent 5137110.
Pickles, C.A., 2009. Thermodynamic analysis of the selec-
tive chlorination of electric arc furnace dust. J. Hazard.
Mater., 166, 1030–1042.
Strohmeier, G., Bonestell, J.E., 1996. Steelworks residues
and the Waelz kiln treatment of electric arc furnace
dust. Iron Steel Eng. 73, 4.
Tsubone, A., Momiyama, T., Inoue, M., Chairaksa, R.,
Matsubae, K., Miki, T., Nagasaka, T., 2012. Dust
injection technology for reducing dust treatment bur-
den. Iron Steel Technol. 9, 184–193.
Tsutsumi, H., Yoshida, S., Tetsumoto, M., 2010. Features of
FASTMET ® process. Kobelco Technol. Rev. 20, 85–92.
United States Environmental Protection Agency, 1991. Land
Disposal Restrictions for Electric Arc Furnace Dust
(K061)—Federal Register Notice, August 19, 1991.
https://www.epa.gov/rcra/land-disposal-restrictions
-electric-arc-furnace-dust-k061-federal-register-notice
-august-19.
Wang, J., Zhang, Y., Cui, K., Fu, T., Gao, J., Hussain, S.,
AlGarni, T.S., 2021. Pyrometallurgical recovery of zinc
and valuable metals from electric arc furnace dust—A
review. J. Cleaner Prod. 298, 126788.
World Steel Association, 2020. 2020 World steel in fig-
ures. Available at https://worldsteel.org/wp-content
/uploads/2020-World-Steel-in-Figures.pdf
Youcai, Z., Stanforth, R., 2000b. Integrated hydrometal-
lurgical process for production of zinc from electric
arc furnace dust in alkaline medium. J. Hazard. Mater.
B80, 223–240.

Previous Page Next Page

Extracted Text (may have errors)

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1671
REFERENCES
Antuñano, N., Cambra, J.F., Arias, P.L, 2019.
Hydrometallurgical processes for Waelz oxide valorisa-
tion—An overview: Process Saf. Environ. Prot., 129,
308–20.
Anon, 1989. Recovery of zinc from EAF dust by the Waelz
process. Steel Times 217, 194–195.
Binnemans, K., Jones, P.T., Fernández, Á.M., Torres, V.M.,
2020. Hydrometallurgical Processes for the Recovery
of Metals from Steel Industry By-Products: A Critical
Review. J. Sustain. Metall., 6, 505–40.
Chairaksa, R., Inoue, Y., Umeda, N., Itoh, S., Nagasaka,
T., 2015. New pyrometallurgical process of EAF dust
treatment with CaO addition, Int. Journ. Min. Metall.
Mater. 22, 788.
Chairaksa, R., Maruyama, K., Miki, T., Nagasaka, T., 2016.
Hydrometallurgy 159, 120–125.
Da Silva, M.C., Bernardes, A.M., Bergmann, C.P., Tenório,
J.A.S., Espinosa, D.C.R., 2008. Characterisation of
electric arc furnace dust generated during plain car-
bon steel production, Ironmaking &Steelmaking 35,
315–320.
De Buzin, P.J.W.K., Heck, N.C., Vilela, A.C.F., 2017. EAF
dust: An overview on the influences of physical, chemi-
cal, and mineral features on its recycling and waste
incorporation routes, J. Mat. Res. Tech. 6, 194–202.
European Agency for Safety and Health at Work, 2006.
Regulation (EC) no. (1907/2006)—Registration,
Evaluation, Authorisation and Restriction of Chemicals
(REACH). https://osha.europa.eu/en/legislation
/directives/regulation-ec-no-1907-2006-of-the
-european-parliament-and-of-the-council.
Gamutan, J., Koide, S., Sasaki, Y., Nagasaka, T., 2024.
Selective dissolution and kinetics of leaching zinc from
lime treated electric arc furnace dust by alkaline media.
Journal of Environmental Chemical Engineering 12,
111789.
Han, Z., Holappa, L., 2003. Bubble bursting phenomenon
in Gas/Metal/Slag systems. Metall. Mater. Trans. B 34,
525–532.
Havlik, T., Souza, B.V., Bernardes, A.M., Schneider,
I.A.H., Miskufova, A., 2006. Hydrometallurgical pro-
cessing of carbon steel EAF dust. J. Hazard. Mater.,
135, 311–318.
International Energy Agency, 2020. Iron and Steel
Technology Roadmap Towards More Sustainable
Steelmaking, 103. Available at https://www.iea.org
/reports/iron-and-steel-technology-roadmap
Itoh, S., Tsubone, A., Matsubae, K., Nakajima, K.,
Nagasaka, T., 2008. New EAF Dust Treatment Process
with the Aid of Strong Magnetic Field, ISIJ Int. 48,
1339–1344.
Langová, Š. and Matýsek, D., 2010. Zinc recovery from
steel-making wastes by acid pressure leaching and hema-
tite precipitation. Hydrometallurgy, 101, 171–173.
Levenspiel, O., 1999. Chemical Reaction Engineering, 3rd
ed. New York, USA: John Wiley &Sons.
Nakajima, K., Matsubae-Yokoyama, K., Nakamura, S.,
Itoh, S., Nagasaka, T., 2008. Substance flow analysis
of zinc associated with iron and steel cycle in Japan,
and environmental assessment of EAF dust recycling
process, ISIJ Int. 48, 1478–1483.
Nakayama, T., Taniishi, H., 2011. Dust recycling technol-
ogy for electric arc furnace using RHF. Nippon. Steel
Eng. Tech. Rev. 2, 25–29.
Nakayama, M., 2012. EAF dust treatment for high metal
recovery. SEAISI Q. J. 41, 22–26.
Nagasaka, T., Itoh, S., Yokoyama, K., Nakajima, K.,
Japanese Patent 5137110.
Pickles, C.A., 2009. Thermodynamic analysis of the selec-
tive chlorination of electric arc furnace dust. J. Hazard.
Mater., 166, 1030–1042.
Strohmeier, G., Bonestell, J.E., 1996. Steelworks residues
and the Waelz kiln treatment of electric arc furnace
dust. Iron Steel Eng. 73, 4.
Tsubone, A., Momiyama, T., Inoue, M., Chairaksa, R.,
Matsubae, K., Miki, T., Nagasaka, T., 2012. Dust
injection technology for reducing dust treatment bur-
den. Iron Steel Technol. 9, 184–193.
Tsutsumi, H., Yoshida, S., Tetsumoto, M., 2010. Features of
FASTMET ® process. Kobelco Technol. Rev. 20, 85–92.
United States Environmental Protection Agency, 1991. Land
Disposal Restrictions for Electric Arc Furnace Dust
(K061)—Federal Register Notice, August 19, 1991.
https://www.epa.gov/rcra/land-disposal-restrictions
-electric-arc-furnace-dust-k061-federal-register-notice
-august-19.
Wang, J., Zhang, Y., Cui, K., Fu, T., Gao, J., Hussain, S.,
AlGarni, T.S., 2021. Pyrometallurgical recovery of zinc
and valuable metals from electric arc furnace dust—A
review. J. Cleaner Prod. 298, 126788.
World Steel Association, 2020. 2020 World steel in fig-
ures. Available at https://worldsteel.org/wp-content
/uploads/2020-World-Steel-in-Figures.pdf
Youcai, Z., Stanforth, R., 2000b. Integrated hydrometal-
lurgical process for production of zinc from electric
arc furnace dust in alkaline medium. J. Hazard. Mater.
B80, 223–240.

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1670 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
the leaching reactions were also evaluated as shown in the
Arrhenius plots in Figure 5. It was found that a significant
variation in slope arises at 50°C, confirming the change in
the rate controlling step. From 25°C to 50°C, the activation
energies were estimated as 57.6 kJ/mol, 59.8 kJ/mol, and
88.0 kJ/mol and from 50°C to 70°C, the activation ener-
gies were calculated as 33.8 kJ/mol, 41.0 kJ/mol, and 40.3
kJ/mol for NaOH, KOH, and LiOH solutions, respec-
tively. Strictly speaking, the over-all rate of reaction should
not change drastically under certain conditions but should
change gradually from one mechanism to the other in the
mixed controlled region. As such, the exact activation ener-
gies must be slightly smaller than the calculated values in
the higher temperature region (50°C to 70°C) and slightly
larger in the lower temperature region (25°C to 50°C). This
confirms the identified rate-controlling mechanisms in the
present work, with a change from chemical reaction con-
trol to product layer diffusion control. These findings indi-
cate that higher temperatures and finer particle size are key
to maximize dissolution of zinc from CaO-treated EAFD
using alkaline solutions.
Calcination of Leach Residues
According to the XRD data obtained for the leach residues
shown in Figure 2(c-e), only Ca2Fe2O5 and Ca3Fe2(OH)12
remain after alkaline leaching of CaO-treated EAFD, con-
firming the almost complete dissolution of zinc into the
leachate. Both Ca2Fe2O5 and Ca3Fe2(OH)12 contain iron
oxide and calcium oxide, making the residues excellent raw
materials for ironmaking or as fluxing materials during the
steelmaking process. However, Ca3Fe2(OH)12 contains a
significant quantity of crystalline water which may need to
be removed prior to recycling in the iron and steelmaking
process via a calcination step. Dehydration reactions are
usually endothermic and therefore consumes energy, sug-
gesting that calcination prior to recycling may be necessary
to minimize fuel consumption and contamination of the
final steel product.
While XRD data of the calcined leach residues at 100°C
and 300°C still indicated the presence of Ca3Fe2(OH)12,
it was found that the samples were composed only of
Ca2Fe2O5 after calcination at 500°C for 4 hours, as shown
in Figure 2(f). SEM-EDS analysis of the calcined leach resi-
due under the same conditions is also shown in Figure 3(c).
Alongside Ca2Fe2O5 (Point 8 and 9), independent spheri-
cal particles of CaO were also found (Point 7), suggesting
that the calcination reaction proceeded according to the
following equation:
6H2O Ca3 Fe2 OHh12 Ca2 Fe2O CaO
5 -=++^(5)
The above reaction was accompanied by a dehydration
reaction that eliminated the crystalline-bound water and
a dissociation reaction forming Ca2Fe2O5 and CaO. The
change in weight of the sample before and after calcination
confirms the removal of water while the presence of inde-
pendent CaO particles in the calcined product confirms the
dissociation reaction above. From this, a solid by-product
containing Ca2Fe2O5 and CaO only could therefore be
obtained by calcination at 500°C for 4 hours, an excellent
material for iron and steelmaking, ensuring sustainability
of the whole process.
CONCLUSIONS
Findings from the current work demonstrate that con-
version from ZnFe2O4 to ZnO and Ca2Fe2O5 via a non-
carbothermic CaO-treatment followed by alkaline leaching
enables near-complete zinc extraction, which is critical
for green and sustainable EAFD recycling. The complete
reduction of ZnFe2O4 to ZnO and Ca2Fe2O5 through the
CaO-treatment process was achieved at 1100°C for 5 hours
in air, with Ca:Fe molar ratio of 1.3.
Meanwhile, alkaline leaching of the CaO-treated EAFD
showed that NaOH solution enables the fastest and highest
zinc dissolution, followed by KOH and LiOH. However,
KOH may be a more practical option due to its potentially
higher zinc extraction capacity than NaOH, albeit slow
(Gamutan et al., 2024). Optimal zinc leaching conditions
were achieved at 70°C and a S:L ratio of 1:300 (mg:ml)
using 2M NaOH solution at 99% zinc recovery after 2
hours. The negligible dissolution of iron and calcium in
alkaline solutions suggests minimal impurities in the leach-
ate, enabling recovery of high-purity zinc metal without the
need for an extra refining step. Kinetics analysis of the zinc
leaching process indicated a change from chemical reaction
control to product layer diffusion control at 50°C, implying
that higher temperatures and finer particle size are key to
maximize zinc extraction in the proposed process.
Finally, calcination of the leach residues at 500°C for
4 hours in air allowed conversion of Ca3Fe2(OH)12 to
Ca2Fe2O5 and CaO coupled with the removal of water.
Calcination resulted in residues containing only Ca2Fe2O5
and CaO, both of which are suitable for direct recycling
back into the iron and steelmaking process, paving the
way for a sustainable EAFD recycling loop. Compared to
strictly pyrometallurgical or hydrometallurgical methods,
the proposed combination treatment does not require the
use of carbon and has lower energy consumption, provid-
ing a more sustainable alternative to recover both zinc and
iron from EAFD.

Previous Page Next Page

Extracted Text (may have errors)

1670 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
the leaching reactions were also evaluated as shown in the
Arrhenius plots in Figure 5. It was found that a significant
variation in slope arises at 50°C, confirming the change in
the rate controlling step. From 25°C to 50°C, the activation
energies were estimated as 57.6 kJ/mol, 59.8 kJ/mol, and
88.0 kJ/mol and from 50°C to 70°C, the activation ener-
gies were calculated as 33.8 kJ/mol, 41.0 kJ/mol, and 40.3
kJ/mol for NaOH, KOH, and LiOH solutions, respec-
tively. Strictly speaking, the over-all rate of reaction should
not change drastically under certain conditions but should
change gradually from one mechanism to the other in the
mixed controlled region. As such, the exact activation ener-
gies must be slightly smaller than the calculated values in
the higher temperature region (50°C to 70°C) and slightly
larger in the lower temperature region (25°C to 50°C). This
confirms the identified rate-controlling mechanisms in the
present work, with a change from chemical reaction con-
trol to product layer diffusion control. These findings indi-
cate that higher temperatures and finer particle size are key
to maximize dissolution of zinc from CaO-treated EAFD
using alkaline solutions.
Calcination of Leach Residues
According to the XRD data obtained for the leach residues
shown in Figure 2(c-e), only Ca2Fe2O5 and Ca3Fe2(OH)12
remain after alkaline leaching of CaO-treated EAFD, con-
firming the almost complete dissolution of zinc into the
leachate. Both Ca2Fe2O5 and Ca3Fe2(OH)12 contain iron
oxide and calcium oxide, making the residues excellent raw
materials for ironmaking or as fluxing materials during the
steelmaking process. However, Ca3Fe2(OH)12 contains a
significant quantity of crystalline water which may need to
be removed prior to recycling in the iron and steelmaking
process via a calcination step. Dehydration reactions are
usually endothermic and therefore consumes energy, sug-
gesting that calcination prior to recycling may be necessary
to minimize fuel consumption and contamination of the
final steel product.
While XRD data of the calcined leach residues at 100°C
and 300°C still indicated the presence of Ca3Fe2(OH)12,
it was found that the samples were composed only of
Ca2Fe2O5 after calcination at 500°C for 4 hours, as shown
in Figure 2(f). SEM-EDS analysis of the calcined leach resi-
due under the same conditions is also shown in Figure 3(c).
Alongside Ca2Fe2O5 (Point 8 and 9), independent spheri-
cal particles of CaO were also found (Point 7), suggesting
that the calcination reaction proceeded according to the
following equation:
6H2O Ca3 Fe2 OHh12 Ca2 Fe2O CaO
5 -=++^(5)
The above reaction was accompanied by a dehydration
reaction that eliminated the crystalline-bound water and
a dissociation reaction forming Ca2Fe2O5 and CaO. The
change in weight of the sample before and after calcination
confirms the removal of water while the presence of inde-
pendent CaO particles in the calcined product confirms the
dissociation reaction above. From this, a solid by-product
containing Ca2Fe2O5 and CaO only could therefore be
obtained by calcination at 500°C for 4 hours, an excellent
material for iron and steelmaking, ensuring sustainability
of the whole process.
CONCLUSIONS
Findings from the current work demonstrate that con-
version from ZnFe2O4 to ZnO and Ca2Fe2O5 via a non-
carbothermic CaO-treatment followed by alkaline leaching
enables near-complete zinc extraction, which is critical
for green and sustainable EAFD recycling. The complete
reduction of ZnFe2O4 to ZnO and Ca2Fe2O5 through the
CaO-treatment process was achieved at 1100°C for 5 hours
in air, with Ca:Fe molar ratio of 1.3.
Meanwhile, alkaline leaching of the CaO-treated EAFD
showed that NaOH solution enables the fastest and highest
zinc dissolution, followed by KOH and LiOH. However,
KOH may be a more practical option due to its potentially
higher zinc extraction capacity than NaOH, albeit slow
(Gamutan et al., 2024). Optimal zinc leaching conditions
were achieved at 70°C and a S:L ratio of 1:300 (mg:ml)
using 2M NaOH solution at 99% zinc recovery after 2
hours. The negligible dissolution of iron and calcium in
alkaline solutions suggests minimal impurities in the leach-
ate, enabling recovery of high-purity zinc metal without the
need for an extra refining step. Kinetics analysis of the zinc
leaching process indicated a change from chemical reaction
control to product layer diffusion control at 50°C, implying
that higher temperatures and finer particle size are key to
maximize zinc extraction in the proposed process.
Finally, calcination of the leach residues at 500°C for
4 hours in air allowed conversion of Ca3Fe2(OH)12 to
Ca2Fe2O5 and CaO coupled with the removal of water.
Calcination resulted in residues containing only Ca2Fe2O5
and CaO, both of which are suitable for direct recycling
back into the iron and steelmaking process, paving the
way for a sustainable EAFD recycling loop. Compared to
strictly pyrometallurgical or hydrometallurgical methods,
the proposed combination treatment does not require the
use of carbon and has lower energy consumption, provid-
ing a more sustainable alternative to recover both zinc and
iron from EAFD.

1685
Investigation of Process Intensification Role in
Solid–Liquid Separation Techniques for the Recyclable
Samarium-Cobalt Magnet
Zainab Nasrullah, Frank Agyemang, Oluwatosin Adeyebayo, John Dhuol
Department of Metallurgical and Materials Engineering, Montana Technological University, Butte, Montana. USA
Richard LaDouceur
Department of Mechanical Engineering, Montana Technological University, Butte, Montana, USA
ABSTRACT: To sustain the circular economy, defense applications, and other renewable technologies,
recycling rare earth elements (REEs) and other critical elements from their secondary resources is important.
This cause has resulted in rigorous research and development for viable extraction and separation of REEs.
Previously, Sm-Co recycling has been done with technologies, which fall under the categories of pyrometallurgy,
physical separation, and hydrometallurgy. All these methods have limitations associated with energy, cost, and
environment. Reportedly, the chemical leaching technology has successfully recovered and separated Sm-Co.
Still, it has limitations associated with slow mass transfer and leaching kinetics, and there is a need to intensify
the process to make it time efficient. This approach has also adversely impacted the environment by an extensive
use of toxic, corrosive, non-selective, and expensive reagents. In this research study, chemical leaching of Sm-Co
was performed using this new class of solvents, Deep Eutectic Solvents (DESs), which fall under the category
of ionometallurgy. Four different DESs were used, proven to be green, non-toxic, biodegradable, cheap, and
selective for cobalt over samarium by 82% leaching conversion. To improve the slow mass transfer and leaching
time, this new technology of resonant vibratory mixing (RVM) was also tested. RVM intensifies mixing by
establishing near instantaneous, low energy mixing conditions through resonance. It has been shown to improve
the adsorption kinetics and was tested for the leaching kinetics. Four combinations of DESs were prepared, which
are made up of two quaternary salts: Choline Chloride and Tetra Butyl Ammonium Chloride, and three organic
compounds: Oxalic Acid, Urea, and Ethylene Glycol. These combinations were used for chemical leaching of
Sm-Co with leaching factors of time, temperature, and type of DESs. After leaching, the samples were tested
with and without resonant vibratory mixing with conditions of time, intensity (%),and type of DESs. Samples
were analysed with Induced Coupled Plasma–Optical Spectroscopy (ICP–OES). Future work will involve a life-
cycle assessment to assess the RVM technology with other conventional mixers, and an extensive study of DES
properties to improve selective leaching.
INTRODUCTION
Together with yttrium (Y), scandium (Sc), and lanthanides,
the rare earth elements (REE) are a collection of 17 chemi-
cally related elements [1]. Due to their distinctive physical
and chemical characteristics, rare earth elements (REEs) are
valuable resources that are necessary for a wide range of
modern technological applications, including metallurgy,
machine building, radio electronics, instrument engineer-
ing, nuclear engineering, and manufacturing [1], [2], [3].

Previous Page Next Page

Extracted Text (may have errors)

1685
Investigation of Process Intensification Role in
Solid–Liquid Separation Techniques for the Recyclable
Samarium-Cobalt Magnet
Zainab Nasrullah, Frank Agyemang, Oluwatosin Adeyebayo, John Dhuol
Department of Metallurgical and Materials Engineering, Montana Technological University, Butte, Montana. USA
Richard LaDouceur
Department of Mechanical Engineering, Montana Technological University, Butte, Montana, USA
ABSTRACT: To sustain the circular economy, defense applications, and other renewable technologies,
recycling rare earth elements (REEs) and other critical elements from their secondary resources is important.
This cause has resulted in rigorous research and development for viable extraction and separation of REEs.
Previously, Sm-Co recycling has been done with technologies, which fall under the categories of pyrometallurgy,
physical separation, and hydrometallurgy. All these methods have limitations associated with energy, cost, and
environment. Reportedly, the chemical leaching technology has successfully recovered and separated Sm-Co.
Still, it has limitations associated with slow mass transfer and leaching kinetics, and there is a need to intensify
the process to make it time efficient. This approach has also adversely impacted the environment by an extensive
use of toxic, corrosive, non-selective, and expensive reagents. In this research study, chemical leaching of Sm-Co
was performed using this new class of solvents, Deep Eutectic Solvents (DESs), which fall under the category
of ionometallurgy. Four different DESs were used, proven to be green, non-toxic, biodegradable, cheap, and
selective for cobalt over samarium by 82% leaching conversion. To improve the slow mass transfer and leaching
time, this new technology of resonant vibratory mixing (RVM) was also tested. RVM intensifies mixing by
establishing near instantaneous, low energy mixing conditions through resonance. It has been shown to improve
the adsorption kinetics and was tested for the leaching kinetics. Four combinations of DESs were prepared, which
are made up of two quaternary salts: Choline Chloride and Tetra Butyl Ammonium Chloride, and three organic
compounds: Oxalic Acid, Urea, and Ethylene Glycol. These combinations were used for chemical leaching of
Sm-Co with leaching factors of time, temperature, and type of DESs. After leaching, the samples were tested
with and without resonant vibratory mixing with conditions of time, intensity (%),and type of DESs. Samples
were analysed with Induced Coupled Plasma–Optical Spectroscopy (ICP–OES). Future work will involve a life-
cycle assessment to assess the RVM technology with other conventional mixers, and an extensive study of DES
properties to improve selective leaching.
INTRODUCTION
Together with yttrium (Y), scandium (Sc), and lanthanides,
the rare earth elements (REE) are a collection of 17 chemi-
cally related elements [1]. Due to their distinctive physical
and chemical characteristics, rare earth elements (REEs) are
valuable resources that are necessary for a wide range of
modern technological applications, including metallurgy,
machine building, radio electronics, instrument engineer-
ing, nuclear engineering, and manufacturing [1], [2], [3].