Presented at the XXIV Nordic Concrete Research Symposium in Stockholm, August 17-19, 2022.

1. Tobias Danner & Harald Justnes, XXIV NCR Symposium 2022, Stockholm
1
Bauxite residue as SCM
Approaches to reduce the alkali content
alcircle.com

2. Bauxite residue (BR)
/red mud
• Waste product from Bayer Process (Al2O3)
• Alkaline hazardous waste slurry often
disposed in open ponds
• ~150 mio t. produced annually
• ~4600 mio t. global inventory (2018)
• Cement industry in demand for alternative
high volume clinker replacement materials
Hydro.com
H2020harare.eu
2 (10)

3. Bauxite residue as SCM
(Hydro BR)
Oxides BR
CaO 1.7
SiO2 16.0
Al2O3 18.9
Fe2O3 37.9
TiO2 6.2
MgO <0.1
K2O 0.1
Na2O 9.6
LOI 7.8
SUM 98.6
Oxides BR
CaO 1.7
SiO2 16.0
Al2O3 18.9
Fe2O3 37.9
TiO2 6.2
MgO <0.1
K2O 0.1
Na2O 9.6
LOI 7.8
SUM 98.6
Katoite
AFm
CH
3 (10)
Hydrated pastes of BR and CH
• Fe/Al-oxides and hydroxides;
TiO2, quartz, sodalite/cancrinite
(DSP)
• Amorphous phase (43%)
• Pozzolanic reactive material
(BR/Ca(OH)2 pastes)
• High alkali content (easy soluble)
‒ Effect on hydration, ASR,…

4. Hydrothermal process
• BR + CH + excess water + T
• Filtration and drying
• Removal of water soluble alkalis
• Na-Ca cation exchange in DSP
Na6(Al6Si6O24)·2NaX·H2O → Ca6(Al6Si6O24)·2CaX·H2O
• ~70 % reduction in Na2O in washed and dried BR
• BUT reduced chemical reactivity
CaO neutralization
4 (10)
Gao et al., Processes, Vol.8, No. 6 2018

5. Co-Calcination with kaolinite
• Aim to bind easy soluble Na in stable / non soluble Na-
rich phases
• Blends of 70% BR and 30% Kaolinite
800 ºC
1000 ºC
1100 ºC
• Metakaolin formation at 800 ºC
• Decreased reactivity (bound water) with increased
alkali binding in nepheline
R3 pastes
5 (10)
AFm
Sodalite
Nepheline (Na3K(Al4Si4O16)

6. Acid neutralization
Na in solution
(mg/L)
Total Na2O
reduction (%)
Acetic acid 5650 79.3%
H2O_1 632 88.4%
H2O_2 190 91.2%
Oxides BR AR-BR_sb 1 AR-BR_bb 2
(Weight %)
CaO 1.7 0.2 0.3
SiO2 16.0 14.0 15.8
Al2O3 18.9 15.1 16.0
Fe2O3 37.9 49.0 42.8
TiO2 6.2 8.0 7.0
Na2O 9.6 0.9 1.7
Washing BR with diluted acetic acid (0.5 M),
and destilled water
Sodium in solution (flame spectroscopy)
Residual sodium in dried BR (XRF)
6 (10) Gao et al., Processes, Vol.8, No. 6 2018

7. Alkali reduced bauxite residue (AR-BR) as SCM
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Cement pastes with 20 (+5)% replacement of cement; 28 day hydration
• Similar pozzolanic activity of BR and AR-BR
• Increased bound water (hydration products) and decreased CH confirmed with TGA
CH
Et
Hc
Mc

8. Alkali reduced bauxite residue (AR-BR) as SCM
8 (10)
Mortar compressive strength
- 20% replacement of PC
(EN 196-1)

9. Potential AR-BR production cycle
9 (10)
Acetic
anhydride

10. Summary
• BR is a large volume waste material that
could be used as SCM
• Alkali reduction necessary
• 90 % reduction by treatment with acetic acid
• Promising results with regard to pozzolanic
activity and 28-day strength in mortars with
20% cement replacement
• Potential to be implemented in Al2O3
production line and improve waste
management
10 (10)
lightmetalage.com

11. Thank you for your attention
The results presented in this paper are part of the research project DARE2C;
Durable Aluminium Reinforced Environmentally-friendly Concrete Construction,
supported by grant no. 269767 from the Research Council of Norway.
Industrial partners are Hydro, Norcem, Veidekke and Overhalla Betong.

12. Alkali reduced bauxite residue (AR-BR) as SCM
12
Isothermal calorimetry of cement pastes with 20 (+5)% replacement by BR and AR-BR (+LL)