XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1243
0.57 mol/L, there is a drop in the recovery percentage. This
shows that the concentration of oxalic acid plays a vital role
in the dissolution of ACL tailings. The recovery of P and
Fe kept increasing till 0.57 however, the REE dissolution
remained constant for 0.5 and 0.57 mol/L, dropping at
0.8 mol/L. This is plausible due to the availability of extra
oxalate, which forms REE oxalates. The formation of REE
oxalates tends to co-precipitate some of the iron and phos-
phorus along with the REEs. It is to be noted that a thresh-
old concentration of oxalate is required for this to happen.
Second-Stage Leaching
The oxalic acid leach residue was thoroughly washed, fil-
tered, dried, and then subjected to 0.2 mol/L EDTA at
pH 10 for an hour under room temperature. The results
obtained are shown in Figure 9. The temperature scale in
the graph represents the temperature at which the oxalic
acid leach was carried out. It is to be noted that the EDTA
leach was carried out at room temperature, and the oxalate
leach residue was obtained at different temperatures.
Figure 9 shows that the remaining REE in the residue
tends to form a complex with the EDTA. However, with
the oxalate leach residue from 85°C, EDTA does not tend
to complex with the REE that dropped out of the solution.
One plausible reason is that the REE did not precipitate as
REE oxalate it is either still hosted in the phosphate and
sulphate matrix or is trapped, making it harder for EDTA
to leach. However, this behaviour has to be further stud-
ied by understanding the association of REE in the oxalate
residue and the solution chemistry of the EDTA leach test.
CONCLUSION
In this study, the behaviour of REE from ACL tailings in
the flowsheet proposed by Lazo et al. (2018) was stud-
ied to determine the applicability of the flowsheet. It was
observed that the ACL tailings had a very rapid reaction
rate in the oxalic acid leach. Most of the reaction occurred
within the first hour in the oxalic acid leaching of the tail-
ings. It was observed that the REE also dissolved in the first
stage, and it dropped out of the solution only at 85°C. It
was also noted that the P, Fe, and REE dissolution were
higher at 0.5 mol/L of oxalic acid than at 0.8 mol/L. This
is because of the excess oxalate, which forms REE oxalates.
The formation of REE oxalates tends to co-precipitate
iron and phosphorus at a particular threshold concentra-
tion of oxalate. From the results obtained, it was seen that
the behaviour of ACL tails differs from that of the ores.
The oxalic acid leach residue was washed, filtered, and sub-
jected to 0.2 mol/L EDTA under atmospheric conditions.
EDTA tends to dissolve the remaining REE in the oxalate
leach residue. However, the REE dissolution for the oxalate
residue at higher temperatures was less than 5%. One plau-
sible reason for this behaviour is that the REE doesn’t form
REE oxalate and is still trapped in the Fe and P matrix.
Based on the results obtained from this study, it is seen that
significant recovery has been achieved by processing mine
tailings. Moreover, retreating tailings aids in returning the
REE inventory lost and reduces the waste generated, which
aligns with the principles of circular economy.
ACKNOWLEDGMENTS
The research is supported by Lynas Corporation Ltd and the
Mineral Research Institute of Western Australia (MRIWA).
The authors thank Sandrine Symons for her contribu-
tion towards the work. We thank Mujesira Vukancic and
Bernard Mwango for their support with the necessary lab
equipment and ICP-OES.
REFERENCES
Barakos, G., Dyer, L., &Hitch, M. (2022). The long uphill
journey of Australia’s rare earth element industry:
challenges and opportunities. International Journal of
Mining, Reclamation and Environment, 36(9), 651–670.
doi: 10.1080/17480930.2022.2127248.
Cánovas, C.R., Chapron, S., Arrachart, G., &Pellet-
Rostaing, S. (2019). Leaching of rare earth elements
(REEs) and impurities from phosphogypsum: A pre-
liminary insight for further recovery of critical raw
materials. Journal of Cleaner Production, 219, 225–235.
doi: 10.1016/j.jclepro.2019.02.104.
0
10
20
30
40
50
60
70
80
90
100
OA Leach Liquor
EDTA Leach Liquor
Figure 9. T-REE dissolution of ACL tails in oxalic acid and
EDTA
T-EEDisolton(
)
0.57 mol/L, there is a drop in the recovery percentage. This
shows that the concentration of oxalic acid plays a vital role
in the dissolution of ACL tailings. The recovery of P and
Fe kept increasing till 0.57 however, the REE dissolution
remained constant for 0.5 and 0.57 mol/L, dropping at
0.8 mol/L. This is plausible due to the availability of extra
oxalate, which forms REE oxalates. The formation of REE
oxalates tends to co-precipitate some of the iron and phos-
phorus along with the REEs. It is to be noted that a thresh-
old concentration of oxalate is required for this to happen.
Second-Stage Leaching
The oxalic acid leach residue was thoroughly washed, fil-
tered, dried, and then subjected to 0.2 mol/L EDTA at
pH 10 for an hour under room temperature. The results
obtained are shown in Figure 9. The temperature scale in
the graph represents the temperature at which the oxalic
acid leach was carried out. It is to be noted that the EDTA
leach was carried out at room temperature, and the oxalate
leach residue was obtained at different temperatures.
Figure 9 shows that the remaining REE in the residue
tends to form a complex with the EDTA. However, with
the oxalate leach residue from 85°C, EDTA does not tend
to complex with the REE that dropped out of the solution.
One plausible reason is that the REE did not precipitate as
REE oxalate it is either still hosted in the phosphate and
sulphate matrix or is trapped, making it harder for EDTA
to leach. However, this behaviour has to be further stud-
ied by understanding the association of REE in the oxalate
residue and the solution chemistry of the EDTA leach test.
CONCLUSION
In this study, the behaviour of REE from ACL tailings in
the flowsheet proposed by Lazo et al. (2018) was stud-
ied to determine the applicability of the flowsheet. It was
observed that the ACL tailings had a very rapid reaction
rate in the oxalic acid leach. Most of the reaction occurred
within the first hour in the oxalic acid leaching of the tail-
ings. It was observed that the REE also dissolved in the first
stage, and it dropped out of the solution only at 85°C. It
was also noted that the P, Fe, and REE dissolution were
higher at 0.5 mol/L of oxalic acid than at 0.8 mol/L. This
is because of the excess oxalate, which forms REE oxalates.
The formation of REE oxalates tends to co-precipitate
iron and phosphorus at a particular threshold concentra-
tion of oxalate. From the results obtained, it was seen that
the behaviour of ACL tails differs from that of the ores.
The oxalic acid leach residue was washed, filtered, and sub-
jected to 0.2 mol/L EDTA under atmospheric conditions.
EDTA tends to dissolve the remaining REE in the oxalate
leach residue. However, the REE dissolution for the oxalate
residue at higher temperatures was less than 5%. One plau-
sible reason for this behaviour is that the REE doesn’t form
REE oxalate and is still trapped in the Fe and P matrix.
Based on the results obtained from this study, it is seen that
significant recovery has been achieved by processing mine
tailings. Moreover, retreating tailings aids in returning the
REE inventory lost and reduces the waste generated, which
aligns with the principles of circular economy.
ACKNOWLEDGMENTS
The research is supported by Lynas Corporation Ltd and the
Mineral Research Institute of Western Australia (MRIWA).
The authors thank Sandrine Symons for her contribu-
tion towards the work. We thank Mujesira Vukancic and
Bernard Mwango for their support with the necessary lab
equipment and ICP-OES.
REFERENCES
Barakos, G., Dyer, L., &Hitch, M. (2022). The long uphill
journey of Australia’s rare earth element industry:
challenges and opportunities. International Journal of
Mining, Reclamation and Environment, 36(9), 651–670.
doi: 10.1080/17480930.2022.2127248.
Cánovas, C.R., Chapron, S., Arrachart, G., &Pellet-
Rostaing, S. (2019). Leaching of rare earth elements
(REEs) and impurities from phosphogypsum: A pre-
liminary insight for further recovery of critical raw
materials. Journal of Cleaner Production, 219, 225–235.
doi: 10.1016/j.jclepro.2019.02.104.
0
10
20
30
40
50
60
70
80
90
100
OA Leach Liquor
EDTA Leach Liquor
Figure 9. T-REE dissolution of ACL tails in oxalic acid and
EDTA
T-EEDisolton(
)