XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1241
The REE dissolution in oxalic acid leaching was less
than 2% in ore, even at elevated temperatures and longer
durations, as seen in Figure 5. These results showed that
oxalic acid attacks the phosphate mineral and selectively
dissolves P and Fe over rare earth elements for ores (Yamini
&Dyer, 2023). However, this behaviour did not apply to
ACL tailings. This is because the ACL tailings have a dif-
ferent mineralogy than the direct ores. Oxalic acid leach
residue was washed, filtered, and dried. An XRD analysis
was done on the dried residue to understand the reaction
better. The XRD plot obtained is shown in Figure 5.
From the XRD plot, we can see that the intensity of
the iron phosphate peak has reduced. This shows that the
iron phosphate matrix has undergone a conversion reac-
tion. Also, the oxalate peaks in the leach residue confirm
the presence of REE oxalate.
Effect of Oxalic Acid Concentration on the Leaching
Efficiency
The feed was subjected to 0.8 mol/L oxalic acid under dif-
ferent temperatures: 25⁰, 45⁰, 65⁰, and 85⁰C. However, the
focus was on leaching the ACL tailings at 25 ⁰C as better
results were obtained and operating at lower temperatures
is economical. The results obtained from the leach test car-
ried out at 25⁰C for 24 hours are presented in Figure 6.
After 24 hours, fresh oxalic acid (0.3 mol/L) was added to
precipitate the dissolved REE as REE oxalate.
The results show that the maximum dissolution was
achieved within the first hour, similar to the 0.57 mol/L
oxalic acid. The curve plateaus after the first 6 hours. When
fresh oxalic acid was introduced, there was a significant dip
in the dissolution of TREE. This shows that the added oxa-
late helps the REE to precipitate as REE oxalate.
Based on the results obtained from the above sections,
it is explicitly seen that maximum dissolution is obtained
in the first hour. Therefore, further studies were conducted
to optimise the results by introducing small doses of oxalic
acid after the first hour. In this experiment, an oxalic acid
0
10
20
30
40
50
60
70
80
90
100
0 3 6 9 12 15 18 21 24
Time (h)
Ore: P Dissolution
Ore: T-REE Dissolution
Leach Residue: P Dissolution
Leach Residue: T-REE Dissolution
Figure 4. P &REE Dissolution in ore and ACL tailings
(0.57 mol/L Oxalic Acid, 85°C, S/L ratio =1:10, 250 rpm)
5 10 15 20 25 30 35 40 45 50 55
Diffraction Angle (2 )
Feed
OA Leach Residue
Monazite (REEPO4)
..Barbosalite (Fe2+Fe3+(PO4)(OH)2)
.SiO2
.Magnesium Sulphate (MgSO4.xH2O)
Oxalate 2-
.Anhydrite
4 )
Figure 5. XRD analysis of oxalate leach residue
Dissolution
(%)
Itnsiy
The REE dissolution in oxalic acid leaching was less
than 2% in ore, even at elevated temperatures and longer
durations, as seen in Figure 5. These results showed that
oxalic acid attacks the phosphate mineral and selectively
dissolves P and Fe over rare earth elements for ores (Yamini
&Dyer, 2023). However, this behaviour did not apply to
ACL tailings. This is because the ACL tailings have a dif-
ferent mineralogy than the direct ores. Oxalic acid leach
residue was washed, filtered, and dried. An XRD analysis
was done on the dried residue to understand the reaction
better. The XRD plot obtained is shown in Figure 5.
From the XRD plot, we can see that the intensity of
the iron phosphate peak has reduced. This shows that the
iron phosphate matrix has undergone a conversion reac-
tion. Also, the oxalate peaks in the leach residue confirm
the presence of REE oxalate.
Effect of Oxalic Acid Concentration on the Leaching
Efficiency
The feed was subjected to 0.8 mol/L oxalic acid under dif-
ferent temperatures: 25⁰, 45⁰, 65⁰, and 85⁰C. However, the
focus was on leaching the ACL tailings at 25 ⁰C as better
results were obtained and operating at lower temperatures
is economical. The results obtained from the leach test car-
ried out at 25⁰C for 24 hours are presented in Figure 6.
After 24 hours, fresh oxalic acid (0.3 mol/L) was added to
precipitate the dissolved REE as REE oxalate.
The results show that the maximum dissolution was
achieved within the first hour, similar to the 0.57 mol/L
oxalic acid. The curve plateaus after the first 6 hours. When
fresh oxalic acid was introduced, there was a significant dip
in the dissolution of TREE. This shows that the added oxa-
late helps the REE to precipitate as REE oxalate.
Based on the results obtained from the above sections,
it is explicitly seen that maximum dissolution is obtained
in the first hour. Therefore, further studies were conducted
to optimise the results by introducing small doses of oxalic
acid after the first hour. In this experiment, an oxalic acid
0
10
20
30
40
50
60
70
80
90
100
0 3 6 9 12 15 18 21 24
Time (h)
Ore: P Dissolution
Ore: T-REE Dissolution
Leach Residue: P Dissolution
Leach Residue: T-REE Dissolution
Figure 4. P &REE Dissolution in ore and ACL tailings
(0.57 mol/L Oxalic Acid, 85°C, S/L ratio =1:10, 250 rpm)
5 10 15 20 25 30 35 40 45 50 55
Diffraction Angle (2 )
Feed
OA Leach Residue
Monazite (REEPO4)
..Barbosalite (Fe2+Fe3+(PO4)(OH)2)
.SiO2
.Magnesium Sulphate (MgSO4.xH2O)
Oxalate 2-
.Anhydrite
4 )
Figure 5. XRD analysis of oxalate leach residue
Dissolution
(%)
Itnsiy