1. THE ENEXAL BAUXITE RESIDUE
TREATMENT PROCESS: INDUSTRIAL
SCALE PILOT PLANT RESULTS
Efthymios Balomenos, Dimitrios
Kastritis, Dimitrios Panias, Ioannis
Paspaliaris, Dimitrios Boufounos
Aluminion of Greece
Laboratory of Metallurgy, NTUA

2. Bauxite Residues (BR)
Bayer Process: 5 kg of Bauxite ore is split into 3 kg of
hydrated alumina and 2 kg of BR (dry basis)

3. Bauxite Residues (BR)
• Produced as a
slurry
• 100 -120 Mt / year
• Usual handling
practice:
Disposed in
sealed or
unsealed artificial
impoundments
Hungary 2010

4. Bauxite Residues (BR)
 Dewatering BR in
Filter Presses
 The filter cake has a
moisture content to 25%,
which makes it easier to
handle
 AoG was one of the first
Western European plants
to apply this technology
 AoG Produces 650,000 t
BR per year
Can this BR cake be a potential resource?

5. Bauxite Residues in AoG
Resource for
•
•
%wt
(dry basis)
Mineral Wool
•
Chemical
Species
Fe2O3
Al2O3
16.22%
CaO
SiO2
10.73%
TiO2
5.93%
Na2O
2.51%
V2O5
0.21%
-SO3
0.60%
-CO2
1.63%
H2O(cry)
8.35%
High Added
production
Value product
Complementary
production with
Pig Iron
reduces energy
consumption
Economic, Zero
Waste process
Resource for Pig-
47.74%
Iron Production
•
6.09%
•
•
Dried BR are dusty and
therefore require
agglomeration prior to
feeding to conventional
reactors (blast
furnace/EAF)
Sodium causes
problems with blast
furnace refractories
Un-economic process

6. ENEXAL BR Treatment
 Use of AMRTEAF technology
allows feeding
without
agglomeration
 No Solid/liquid
wastes in the
process
 Mineral wool
produced at 70%
less energy cost
(no melting req.)

7. ENEXAL BR Treatment
Pig iron standards
%C
%S
%P
%Si
~ 4%
<0.02%
<0.05%
0.4-0.8%
Empirical indexes for mineral wool production
(SiO2 +Al2O3 + TiO2)/(CaO+MgO;
< 1.8
4.9/[(MgO+CaO+Fe2O3 +Na2O + TiO2)/
< 15
(SiO2 +Al2O3)] -0.45
[100 – (SiO2 + Al2O3)]/( SiO2 +Al2O3)
0.8 -1
(SiO2 +Al2O3)/(1.4 MgO+ 0.4 Fe2O3 +
1.3 - 1.4
CaO + TiO2)
Na2O + MgO + CaO
30 – 40
Process Design
Define conditions for
optimum iron recovery
(temperature, carbon addition)
Define physico-chemical
properties of the slag through
appropriate fluxes (CaO, SiO2)
in order to produce a melt
suitable for mineral wool
production
Thermodynamically Model
the Process
Test in Lab, Semi-Industrial
and Industrial Pilot Scale

8. ENEXAL BR Treatment
AoG Pilot Plant
1 MVA AMRT-EAF
(AC, 3-electrode,
dust treating, batch
capacity 1t)
Melt Fiberizing
Line
Static Bed Electric
Dryer
One year of
operation treating 25
tons of BR

9. ENEXAL BR Treatment
AMRT-EAF Carbothemic Smelting
Open bath operation
Continuous feeding 6.65 kg/min
Melt Temperature app 1600oC
Energy Consumption: 1508 kWh/t of BR
Dust in filters 4% wt of feed
Feed
Dry BR (kg)
Silica (kg)
Lime (kg)
Coke (kg)
Total Feed (kg)
Batch
700
126
105
140
1071

10. The AMRT Dust Treating EAF technology
• The EAF treats directly dusty material
feed
• Open bath operation (material reacts
upon contact with the bath)
• Patented PLC system regulates power
supply depending on real time
measurement of melt impendence
10

11. ENEXAL BR Treatment
Pig Iron Production
Produced metal within specification for
use in secondary steel industry, as an up
to 20% steel scrap substitute
High Cr presence due to initial refractory
dissolution (Reft1)
More than 5t pig iron produced in total
Pig Iron
Fe (%wt)
C (%wt)
S (%wt)
P (%wt)
Si (%wt)
Cr (%wt)
Total
Refr1
95.47
3.36
0.26
0.08
0.01
0.82
99.99
Refr2
93.44
4.59
0.07
0.22
1.12
0.50
99.94
White Iron grinding balls
produced from BR iron
(21%wt subs)

12. ENEXAL BR Treatment
Mineral Wool Production
Slag melt within empirical indexes
Fibre with good quality :
 λ = 0,034 W /(mk) [UNI EN 12667]
 Average fiber diameter 7 micron
 Bright color (low Mn content)
 High Mechanical resistance due to high TiO2
Slag
Refr1 Refr2
Fe2O3
5.0
1.1
SiO2
27.6
26.5
CaO
25.3
23.4
Al2O3
20.9
31.1
Cr2O3
3.0
0.1
MgO
8.89
8.3
TiO2
5.6
6.1
Na2O
2.4
1.8
Mineral wool used
inside the plant

13. ENEXAL BR Treatment
BR Mineral
Wool
Commercial
Mineral Wool

14. ENEXAL BR Treatment
 Smelting energy
14.5% in excess of
thermodynamic
requirement
 Overall plant
consumption 2
MWh/t BR
 Exergy Utilization
efficiency 32%
 Increase of
alumina refinery
exergy utilization
by 8 percentile
points

15. ENEXAL BR Treatment
 Up-scaling will bring higher
energy efficiency, especially in
BR drying
 Initial studies show the
process to be profitable
 Break-even point is achieved
with a fairly low mineral wool
price
but
The ENEXAL BR treatment is
successful but it should be a
starting point for further BR
and BR-slag product
development
 Pig iron revenues account for
only 25% of the operating
costs
 Treating the AoG annual BR
production would produce 0.5
Mt of Mineral Wool products

16. Future Research
• The AoG BR also contain app 0.1%wt in REE
(mainly as Sc, Ce and Nd)
• In the ENEXAL process these REE concentrate in
the slag – can they be recovered?
“EURARE: Development of a sustainable exploitation scheme for Europe’s REE ore
deposits”
eres2014.conferences.gr

17. Thank you for attention
The research leading to these results has received funding
from the European Union Seventh Framework Programme
([FP7/2007-2013]) under grant agreement n°