1. RECOVERY OF RARE EARTHS FROM BAUXITE RESIDUE SLAG BY HIGH-PRESSURE ACID LEACHING
MSCA-ETN REDMUD PROJECT
Rodolfo Marin Rivera, Buhle Xakalashe,
Ghania Ounoughene, Koen Binnemans,
Bernd Friedrich, Tom Van Gerven
BR 2018, 9th May

2. TURNING THE BAUXITE RESIDUE INTO AN OPPORTUNITYAl Si Fe Ti Ca
REEs Na
NORM
Ajka BR disaster (Hungary, 2010)
Source for critical metals[1]
Source for low carbon materials[2]
[1] Power, G. et al. (2011). Hydrometallurgy 108, 33-45
[2] Binnemans, K. et al (2015). J. Cleaner Production 99, 17-38

3. Co-dissolution of major elements
RECOVERY OF RARE EARTHS FROM BAUXITE RESIDUE – a brief review
Extraction efficiencies depend on acid concentration. [3]
High acid concentration
High REEs extraction
Co-dissolution of major elements
(Fe, Al, Ti, Si)
Chemical association of Sc(III) with Fe(III)-rich mineral phases.[4]
(EPMA, type JXA F from Jeol Ltd.)
[3] Borra et al. (2014). Miner. Eng. 76, 20–27
[4] Rivera et al. (2017). Miner. Eng. 112, 92–102

4. REEs concentration (mg/kg)
SEPARATION OF IRON FROM REEs
Reductive smelting  Separate Fe from the REEs.[5]
REEs can be further recovered from the slag by acid leaching.
REEs concentration (mg/kg)
Element
Bauxite residue
Slag Sc
98 ± 1.7
124 ± 1.6 Y
66 ± 1.6
106 ± 1.3 La
144 ± 3.0
169 ± 1.5 Nd
65 ± 2.6
112 ± 0.7
REEs Enrichment factor in the slag relative to BR   1.4
[5] Borra et al. (2016). J. Sustain. Metall. 2, 28–37

5. NORM concentration (Bq/kg)
SEPARATION OF IRON FROM REEs
NORM concentration (Bq/kg)
Isotope
Bauxite residue[6-7]
Slag
238U
147
276
232Th
426
613
40K 22
126
 1.5  238U & 232Th
 9  40K
Enrichment of NORMs in the slag relative to BR
EU member must integrate (additional) protection when [8]
238U and 232Th (and their decay products) > 1000 Bq/kg
40K > Bq/kg
[6] Goronovski et al. (2018). J. Clean Prod. 172, 2824–2839
[7] Joyce et al. (2017). Int. J. Life Cycle Assess. 22, 1078–1095
[8]

6. Major chemical components (wt.%)
SEPARATION OF IRON FROM REEs
Major chemical components (wt.%)
Y: yoshiokaite (Al5.4Ca2.7O16Si2.7)
N: nepheline (AlNa0.98O4Si)
P: perovskite (CaTiO3)
Ti: titanate (CaO5SiTi)
Slag XRD analysis
Element
Bauxite residue
Slag Al 10 19 Ca 6 16 Si 3 Ti 4 5 Na 2 Fe 33
Si-dissolution leads to a larger supersaturation of silicic acid  driving force for polymerization.[9-10]
Silica polymerization limits the efficient extraction of REEs from the solid matrix.[11]
[9] Hamouda et al. (2014). Energies 7, 568–590
[10] Tobler et al. (2009). Geochim. Cosmochim. Acta 73, 5377– 5393
[11] Rivera et al. (2018). Miner. Eng. 119, 82-92

7. HIGH-PRESSURE ACID LEACHING OF BAUXITE RESIDUE SLAG
HPAL limits the dissolution of Si and Ti  hydrolysis takes place at high temperatures (> 100 C).[12]
Acid consumption can be reduced and the extraction of REEs can be done selectively
HPAL in a titanium autoclave (Parr Company, series 4560) at different temperatures ( °C).
[12] Huang et al. (2015). Sep. Purif. Technol. 156,

8. HIGH-PRESSURE ACID LEACHING OF BAUXITE RESIDUE SLAG
Extraction of Al, Fe, Ti and Si (L/S: 10, t: 1 h).
High acid concentration  high extraction of Al (> 50 wt.%, 18 g/L) and Fe (> 60 wt.%, 3 g/L)
At temp. > 140 C  Si and Ti dissolution < 1 wt.% (< 0.5 g/L)

9. HIGH-PRESSURE ACID LEACHING OF BAUXITE RESIDUE SLAG
Extraction of REEs (Sc, Y, Nd and La) (L/S: 10, t: 1 h).
High acid concentration  high selectivity for Sc (> 70 wt.%, 12 mg/L)
At T > 100 C  low extraction of other REEs  presumably due to the formation of CaxLn(1-x)TiO3 or a double sulfate (REE2(SO4)3CaSO4). [13-14]
[13] Borra et al. (2017). J. Sustain. Met. 3,
[14] Shrivastava et al. (2004). Bull. Mater. Sci. 27,

10. CONCLUSIONS 95 wt.% Fe was recovered by reductive smelting.
With HPAL low Si and Ti dissolution, particularly at temp. > 150 C.
High acid concentration leads to high Al dissolution (> 50 wt.%, 18 g/L).
High acid concentration (H2SO4) leads to high selectivity for Sc recovery
(> 90 wt.% between C).
Low extraction of REEs with high acid concentration and high temperature, presumably due to the formation of secondary compounds.

11. Thank you very much for your attention
Thank you very much for your attention
The research leading to these results has received funding from the European Community’s Horizon 2020 Programme (H2020/2014–2019) under Grant Agreement No (MSCA- ETN REDMUD). This presentation reflects only the authors’ view, exempting the Community from any liability. Project website: The authors thank Aluminium of Greece for providing the bauxite residue sample.