Combined Carbothermic Reduction of Bauxite Residue
Description: Combined Carbothermic Reduction of Bauxite Residue and Basic Oxygen Furnace Slag for Enhanced Recovery of Fe and Slag Conditioning Buhle Xakalashe, Bernd Friedrich Bauxite Residue Valorisation and Best Practices Conference , 08.05.2018
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slide1. Combined Carbothermic Reduction of Bauxite Residue and Basic Oxygen Furnace Slag for Enhanced Recovery of Fe and Slag Conditioning Buhle Xakalashe, Bernd Friedrich Bauxite Residue Valorisation and Best Practices Conference , 08.05.2018<br>
slide2. Bauxite Residue Major by-product of the bayer process
Limited industrial application (approximately 2%)
Disposal is a challenge: fine particles, high alkalinity
Non-hazardous (European commission) Source: ICSOBA 2011, 188<br>
slide3. Carbothermic Reduction of Bauxite Residue Aluminium of Greece Bauxite Residue Fe recovered to metal phase
(low iron production compared
to primary resources)
High Al2O3 containing slag
High operating temperatures
Fluxed smelting
Lower operating temperatures
‘conventional fluxes‘
Lime, dolomite, wollastonite,
quartz, silica sand
Non conventional fluxing
Enhanced Fe recovery, slag conditioning BR 3C + Fe2O3 = 2Fe + 3CO (1)<br>
slide4. Basic Oxygen Furnace Slag German BOF-slag Fluxing capability
Contains Fe
BOF-slag
By-product in converter steel making
High production volumes
Main uses: aggregates for road
construction and fertilizers
Extraction of Fe and use of gangue components would be a high value application BR BOF
Slag<br>
slide5. Iron Production - Combined smelting of BR and BOF-slag Increases of 16 to 25% theoretically achievable for BOF-slag additions of 23 wt.% to 33 wt.% (FactSage 6.4)<br>
slide6. Experimental Procedure 100kW DC electric arc furnace
(operated 3-6 kW)
Batch mass: 1.5 kg BR
Lignite coke: 0.1 x BR (reductant)
CaO: 0.3 x BR (Baseline fluxing)
BOF-slag: 0.3 x BR (combined fluxing)
Target temperature: 1500oC - 1550oC
Holding time: 1 hour
Controlled cooling (slow cooling)
Slag cooling: 20oC/min<br>
slide7. Product Slag – Theoretical vs Experimental Thermochemical modelling in agreement with experimental results
(exception to Na in high CaO containing slag)
Low residual Fe achieved in the slag (high recoveries to metal)<br>
slide8. Elemental Recoveries A closing mass balance observed, based on comparable product masses to theoretically predicted masses<br>
slide9. XRD analysis of BR and produced slags Both slags contain comparable phases which can be optimised for recovery of valuable elements (Al, Ti and Sc)
The mayenite phase for the CaO fluxed slag can be attributed to the suffient availability CaO<br>
slide10. Summary and Outlook Combined smelting of bauxite residue and BOF-slag was carried out successfully
Combined recovery of iron from bauxite residue and BOF-slag was achieved
BOF-slag is a promising fluxing agent in bauxite residue smelting
Outlook
Optimisation of BOF-slag additions for iron recovery (quality and quantity of the produced metal)
Optimisation of the combined smelting process for downstream recovery of valuable elements (slag chemistry and mineralogy)<br>
slide2. Bauxite Residue Major by-product of the bayer process
Limited industrial application (approximately 2%)
Disposal is a challenge: fine particles, high alkalinity
Non-hazardous (European commission) Source: ICSOBA 2011, 188<br>
slide3. Carbothermic Reduction of Bauxite Residue Aluminium of Greece Bauxite Residue Fe recovered to metal phase
(low iron production compared
to primary resources)
High Al2O3 containing slag
High operating temperatures
Fluxed smelting
Lower operating temperatures
‘conventional fluxes‘
Lime, dolomite, wollastonite,
quartz, silica sand
Non conventional fluxing
Enhanced Fe recovery, slag conditioning BR 3C + Fe2O3 = 2Fe + 3CO (1)<br>
slide4. Basic Oxygen Furnace Slag German BOF-slag Fluxing capability
Contains Fe
BOF-slag
By-product in converter steel making
High production volumes
Main uses: aggregates for road
construction and fertilizers
Extraction of Fe and use of gangue components would be a high value application BR BOF
Slag<br>
slide5. Iron Production - Combined smelting of BR and BOF-slag Increases of 16 to 25% theoretically achievable for BOF-slag additions of 23 wt.% to 33 wt.% (FactSage 6.4)<br>
slide6. Experimental Procedure 100kW DC electric arc furnace
(operated 3-6 kW)
Batch mass: 1.5 kg BR
Lignite coke: 0.1 x BR (reductant)
CaO: 0.3 x BR (Baseline fluxing)
BOF-slag: 0.3 x BR (combined fluxing)
Target temperature: 1500oC - 1550oC
Holding time: 1 hour
Controlled cooling (slow cooling)
Slag cooling: 20oC/min<br>
slide7. Product Slag – Theoretical vs Experimental Thermochemical modelling in agreement with experimental results
(exception to Na in high CaO containing slag)
Low residual Fe achieved in the slag (high recoveries to metal)<br>
slide8. Elemental Recoveries A closing mass balance observed, based on comparable product masses to theoretically predicted masses<br>
slide9. XRD analysis of BR and produced slags Both slags contain comparable phases which can be optimised for recovery of valuable elements (Al, Ti and Sc)
The mayenite phase for the CaO fluxed slag can be attributed to the suffient availability CaO<br>
slide10. Summary and Outlook Combined smelting of bauxite residue and BOF-slag was carried out successfully
Combined recovery of iron from bauxite residue and BOF-slag was achieved
BOF-slag is a promising fluxing agent in bauxite residue smelting
Outlook
Optimisation of BOF-slag additions for iron recovery (quality and quantity of the produced metal)
Optimisation of the combined smelting process for downstream recovery of valuable elements (slag chemistry and mineralogy)<br>