1. Conceptual Flowsheets for Combined Recovery of Fe and Al from Bauxite Residue
Pritii Tam, Chiara Cardenia, Buhle Xakalashe,
Vicky Vassiliadou, Dimitrios Panias, Bernd Friedrich

2. The Bayer Process BAUXITE RESIDUE (RED MUD) Digestion Bauxite ores
Aluminium of Greece (AoG) bauxite residue waste storage at Agios Nikolaos site, Greece. Image by Evangelos Mouchos©.
Digestion
BAUXITE RESIDUE
(RED MUD)
Bauxite ores
Clarification
Precipitation
Calcination
Production:
150 x 106 Mt/year
Stock: 4 x 109 Mt
Alumina

3. Katoite - Ca3Al2(SiO3)(OH)10 Cancrinite - Na6Ca2(AlSiO4)6(CO3)2 (H2O)2
Major Components
Chemical Composition
Mineralogical Phases
Hematite - Fe2O3
Goethite - Fe2O3·H2O
Gibbsite - Al2O3·3H2O
Boehmite – AlOOH
Diaspore – AlOOH
Katoite - Ca3Al2(SiO3)(OH)10
Cancrinite - Na6Ca2(AlSiO4)6(CO3)2 (H2O)2
Calcite - CaCO3
Perovskite- CaTiO3
Anatase - TiO2
Rutile - TiO2
Quartz - SiO2
Composition of Greek Bauxite Residue
XRF Glass Disc (Chemical Analysis) and XRD (Mineralogical Analysis)

4. Iron in Bauxite Residue
5%<Fe2O3<60%
Hematite (Fe2O3)
Goethite (FeO(OH))
Magnetite (Fe3O4)
Fe2O3>Fe3O4>FeO>Fe
Evans (2015)

5. Fe Fe Targeting Iron… BR Flux C BR C Reductive Smelting Smelting
High Temperatures Reduction to Metallic Fe Form
(Pig Iron) Fe BR
Smelting
Flux
Molten Slag C
Reductive Roasting
Reducing Hematite into Magnetic
(Magnetic) Fe
Roasting Reduction
Magnetic Separation BR C
Residue
(Non-Magnetic)

6. Targeting Dielectric Phases using Electromagnetic Energy
Microwave Reduction
Microwave Reduction
Targeting Dielectric Phases using Electromagnetic Energy
(Combination) Fe
Microwave Reduction BR
Electric Arc Furnace, Blast Furnace
Slag for downstream recovery, building materials, mineral wool.
Sinter Residue C
Completing in a fraction of time compared to traditional smelting or roasting furnaces
Roasting Furnaces: Smaller Tube Furnaces and scaling up to Rotary Kilns
Smelting Furnaces: Electric Arc Furnace, Blast Furnace
Other Types: Microwave

7. Targeting Iron… PROCESSES AUTHORS Fe Recovery %
Soda ash/lime roasting process prior to magnetic separation of Fe, and alkaline leaching for Al and Na
Liu et al.
Mishra et al.
Cardenia et al.
51.2%
94% metallization
99% metallization
Smelting using calcite or dolomite as fluxes followed by further downstream processing
Kaussen et al.
Borra et al.
Erçağ and Apak.
Tam et al.
Gharda.
Balomenos et al.
Alkan et al.
Dobos et al.
93%
98%
95%
97%
97.3%
Microwave reductive roasting technique followed by wet magnetic separation
Samouhos et al.
63.3% metallization

8. Aluminium in Bauxite Residue
5%<Al2O3<30%
Simple Al-based Diaspore, Gibbsite, Boehmite
DSP-based Cancrinite, Sodalite,
Ca-based Grossular Products
Leachable
Sodium Aluminate
Evans (2015)

9. Combined Soda Sinter Process Combined Smelting Process
Targeting Aluminium…
Combined Soda Sinter Process
Conversion of Al-mineral Phases to Leachable NaAlO2
(Leachable)
Al,Na BR
Roasting
Alkaline Leaching C
Leached Residue
Na2CO3
Combined Smelting Process
Fe Recovery and Conditioning Slag to Leachable Calcium Aluminates
(Leachable)
Al,Na
Smelting, Calcium Aluminate Conditioning
Alkaline Leaching BR
Flux
Leached Residue C Fe

10. Targeting Aluminium… PROCESSES AUTHORS Al Recovery %
Soda ash/lime roasting process prior to magnetic separation of Fe, and alkaline leaching for Al and Na
Kaussen et al.
Liu et al.
Mishra et al.
Borra et al.
Hertel et al.
89%
75.7%
83.1%
75%
76%
Smelting using calcite or dolomite as fluxes followed by further downstream processing
<50% (Alkaline, below 200 gpl)
90% (High Alkaline,
above 500 gpl)
Erçağ and Apak.
85% (H2SO4 Acid)
Tam et al.
43% (Caustic, below 300 gpl)
Dobos et al.
84% (Nepheline, after smelting)
80% (Calcium Aluminate slag)

11. Flowsheet (I) + Two-step process of recovering firstly Al andBR
+ Two-step process of
recovering firstly Al and
Na, followed by Fe
+ High throughput for the
smelter
+ Reducing Na gaseous
losses in smelting
+ Enriched and conditioned
slag for downstream
processing
- Time, cost and energy
intensive with introduction
of leaching step before
smelting C
Soda Sintering
Na2CO3
NaAlO2
Mild Alkaline Leaching
Al, Na Recovery
Metallic Fe
Carbothermic Reductive Smelting C Fe
Recovery
Flux
Leaching residue for Ti, Sc and REE recovery

12. Flowsheet (II) BR Carbothermic Reductive Smelting C Fe Recovery Flux
Conditioned Slag C
Soda Sintering
Caustic Leaching C
Soda Sintering
Na2CO3
Na2CO3 Cl
Al, Na Recovery
Mild Alkaline Leaching
Al, Ti Recovery
For electrolysis
CaCO3
LR for Ti, Sc and REE recovery
Al, Na Recovery
LR for Ti, Sc and REE recovery
LR for Sc and REE recovery

13. Flowsheet (II) + Enriched and conditioned slag assisting downstream
Carbothermic Reductive Smelting
Flux C Fe
Recovery BR
Conditioned Slag
+ Enriched and conditioned
slag assisting downstream
recovery
+ Mild fluxing conditions
optimising Fe removal
and preparing for Al and
Na recovery
- Na losses in BR smelting
- Excess CaO detrimental to
downstream processing
- High energy consumption
due to two-step
pyrometallurgical process
Metallic Fe
Caustic Leaching
Na2CO3
Al, Na Recovery
LR for Ti, Sc and REE recovery
CaCO3 C Cl
Soda Sintering
Al, Ti Recovery
For electrolysis
LR for Sc and REE recovery
NaAlSiO4, C2AS etc C
Soda Sintering
Na2CO3
NaAlO2
Mild Alkaline Leaching
LR for Ti, Sc and REE recovery
Al, Na Recovery

14. Flowsheet (II) + Single-step heat recovery process targeting Fe, Al
Carbothermic Reductive Smelting
Flux C BR
Conditioned Slag
+ Single-step heat recovery
process targeting Fe, Al
and Na through
conditioning of slag
+ Downstream residue can
be used for building
materials
- Proper conditioning of
leachable calcium
aluminates necessary
- CaCO3 and CaTiO3 inhibit
downstream recoveries
LR for Ti, Sc and REE recovery
Mild Alkaline Leaching C
Na2CO3
Soda Sintering
Al, Na Recovery
LR for Ti, Sc and REE recovery
Caustic Leaching
Na2CO3
Al, Na Recovery
CaCO3 C Cl
Soda Sintering
Al, Ti Recovery
For electrolysis
LR for Sc and REE recovery
CA,C3A,C12A7,C2AS
NaAlO2

15. Flowsheet (II) + Enriched slag targeting Al and Ti chlorides
Conditioned Slag
Carbothermic Reductive Smelting
Flux C Fe
Recovery BR
+ Enriched slag targeting
Al and Ti chlorides
+ AlCl3 easier to introduce
into electrolysis, avoiding
calcination step
- Possible operational
challenges in carbo-
chlorination step
- AlCl3 less favoured in
electrolysis; corrosion
problems and high
maintenance costs
- TiCl4 recovery only
beneficial enriched
LR for Ti, Sc and REE recovery
Mild Alkaline Leaching C
Na2CO3
Soda Sintering
Caustic Leaching
Al, Na Recovery
CaCO3 C Cl
Carbo-chlorination
Al, Ti Recovery
For electrolysis
LR for Sc and REE recovery
AlCl3, TiCl3

16. Flowsheet (III) + Microwave heating selectively focuses on
Microwave Reduction
Water/Mild alkaline Leach
Physical Treatment and Magnetic Separation C
Na2CO3
BR(degassed)
Al, Na Recovery
Slag for Sc and REE recovery
+ Microwave heating
selectively focuses on
moderately absorptive
(dielectrics) materials
+ Highly reduced time of
reduction via microwave
- Cost and size of
microwave equipment,
limited by maximum kWh
- Magnetic separation of Fe
fractions need several
step processing - Degassing needed to
avoid plasma
NaAlO2 Magnetic phase
Fe, Ti
Recovery

17. Flowsheet (IV) + Stoichiometric C assist Al and Na recovery
Carbothermic Reductive Roasting
Water/Mild alkaline Leach
Magnetic Separation C
Na2CO3 BR
Al, Na Recovery
Slag for Sc and REE recovery
Fe, Ti
Recovery
+ Stoichiometric C assist Al
and Na recovery
+ Upscaling easier in
industrial equipment
+ Minimal fluxing with lime
aids downstream
processing
- Fe recovery from
magnetic phase is lesser
compared to metallic Fe
recovery via smelting
- Longer time needed
compared to microwave
process
NaAlO2 Magnetic phase

18. Flowsheet (V) + Previous removal of Al and Na assists the FeBR
+ Previous removal of Al
and Na assists the Fe
metallisation
+ Short duration of
microwave Fe recovery
assists processing
- Sintering and leaching
step before microwave
reduction costs energy
and water.
Soda Sintering
Na2CO3
NaAlO2
Mild Alkaline Leaching
Al, Na Recovery
Microwave Reduction C
Magnetic phase
Physical Treatment and Magnetic Separation
Fe, Ti
Recovery
Slag for Sc and REE recovery

19. Potential Valorisation of BR
Flexible pathways in the recovery of Fe and Al
Dependent on input BR
Composition and Mineralogy
Important factors of consideration
Energy
Reagent/Flux(Downstream conditioning)
Single step vs two-step conversion method
Efficiency

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21. Additional References
Kaußen, F.M.; Friedrich, B. Reductive smelting of red mud for iron recovery. Chemie Ingenieur Technik 2015, 87,
Kaußen, F.M.; Friedrich, B. In Soda sintering process for the mobilisation of aluminium and gallium in red mud Bauxite Residue Valorisation and Best Practices Conference (BR 2015) Leuven, Belgium 2015a; Pontikes, Y., Ed. ACCO: Leuven, Belgium pp
Kaußen, F.M.; Sofras, I.; Friedrich, B. In Carbothermic reduction of red mud in an eaf and subsequent recovery of aluminum from the slag by pressure leaching in caustic solution, Bauxite Residue Valorisation and Best Practices (BR 2015), Leuven, Belgium 5-7 October 2015, 2015b; Pontikes, Y., Ed. ACCO: Leuven, Belgium pp
Erçağ, E.; R. Apak, R. Furnace smelting and extractive metallurgy of red mud: Recovery of tio2, al2o3 and pig iron. J. Chem. Technol. Biotechnol. 1997, 70,
Borra, C.R.; Blanpain, B.; Pontikes, Y.; Binnemans, K.; Van Gerven, T. Comparative analysis of processes for recovery of rare earths from bauxite residue. JOM 2016, 68,
Borra, C.R.; Mermans, J.; Blanpain, B.; Pontikes, Y.; Binnemans, K.; Van Gerven, T. Selective recovery of rare earths from bauxite residue by combination of sulfation, roasting and leaching. Miner. Eng. 2016, 92,
Mishra, B.; Gostu, S. Materials sustainability for environment: Red-mud treatment. Frontiers of Chemical Science and Engineering 2017, 11,
Bruckard, W.J.; Calle, C.M.; R.H. Davidson, R.H.; Glenn, A.M.; Jahanshahi, S.; Somerville, M.A.; Sparrow, G.J.; Zhang, L. Smelting of bauxite residue to form a soluble sodium aluminium silicate phase to recover alumina and soda. Trans. Inst. Min. Metall., Sect. C 2010, 119,