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EFFECT OF ALUMINA ON REDUCTION OF IRON OXIDES

Timo Paananen, M.Sc.Tech Laboratory of Process Metallurgy Department of Process and Environmental Engineering University of Oulu. EFFECT OF ALUMINA ON REDUCTION OF IRON OXIDES. Effect of alumina on reduction of iron oxides. Introduction Solubility of alumina in iron oxides

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EFFECT OF ALUMINA ON REDUCTION OF IRON OXIDES

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  1. Timo Paananen, M.Sc.TechLaboratory of Process MetallurgyDepartment of Process and Environmental EngineeringUniversity of Oulu EFFECT OF ALUMINA ON REDUCTION OF IRON OXIDES Blast Furnace Seminar 30. – 31.3.2004

  2. Effect of alumina on reduction of iron oxides • Introduction • Solubility of alumina in iron oxides • Experiments and results • Analysis • Conclusion Blast Furnace Seminar 30. – 31.3.2004

  3. Previous studies of authors • Dissolved alumina in iron oxide retards the reduction by forming a hercynite cover between the iron oxide and iron* • Reduction is promoted by the formation of hercynite, because the reduction proceeds along the grain boundaries intersected by the hercynite.** * De Bruijn 1990 ** Piepenbrock 1976 Blast Furnace Seminar 30. – 31.3.2004

  4. Disintegration during reduction • Measured for example using RDI-test • Deleterious effect of alumina on RDI • Correlation between the concentration of dissolved alumina and degree of disintegration of iron oxides has been shown in many papers and this is associated with* • hematite-magnetite phase transformation • effect of alumina on amount of calciumferrite • *Shigaki, M. et al. (1986), De, A. et al (1992), Kvak, M. (1997) etc. Blast Furnace Seminar 30. – 31.3.2004

  5. Solubility of alumina into iron oxides Binary phase diagram for system magnetite-hercynite Blast Furnace Seminar 30. – 31.3.2004

  6. Al2O3 (ss) Solubility of alumina into iron oxides Ternary phase diagram for system Fe-Al-O Blast Furnace Seminar 30. – 31.3.2004 /Atlas et al. 1958/

  7. Preparation of samples before reduction • Magnetite concentrate (96.1 wt. % Fe3O4) • Alumina additive was corumdum with a purity of 99.99% • Dissolution temperature (at 900 oC for 2h) • heated three times ”in magnetite conditions” • quenched to water • not heated after the last grinding/pressing process • Dissolution/sintering temperature (at 1395 oC for 2h) • quenched to water Blast Furnace Seminar 30. – 31.3.2004

  8. Experiments • TGA • Sample was held in platinum basket • Briquette warmed up to 950 oC in argon • Reduced by CO/CO2 -gas (90/10) Blast Furnace Seminar 30. – 31.3.2004

  9. + 0 wt.%Al2O3 + 0.95 wt.% Al2O3 + 1.89 wt.% Al2O3 + 3.78 wt.% Al2O3 Reduction curves of porous briquettesAl2O3-addition = [0], [0.95], [1.89], [3.78] wt.%, T = 950 oC Degree of reduction (%) Time Blast Furnace Seminar 30. – 31.3.2004

  10. Redution difference from + 0 wt.% (%-unit) Time (min) Reduction difference of Al-doped porous unsintered briquettes from undoped onesAl2O3-addition=[0], [0.95], [1.89], [3.78] wt.%, T = 950 oC CO/CO2= 90/10 81,5/18,5 73/27 Blast Furnace Seminar 30. – 31.3.2004

  11. SEM image of reduced samples (3000x magnification) Blast Furnace Seminar 30. – 31.3.2004

  12. Reduction curves of sintered (1395 oC) samples ▬ +3.78 wt. % Al2O3 ▬ +0 wt. % Al2O3 Blast Furnace Seminar 30. – 31.3.2004

  13. Reduction difference of sintered samples Al2O3-addition = [0], [3.78] wt.%, T = 950 oC Blast Furnace Seminar 30. – 31.3.2004

  14. SEM image of reduced samples using 500x magnification SEM image (500x) of a doped sample (+3.78 wt. % Al2O3) after reduction. SEM image (500x) of an un-doped sample after reduction. Blast Furnace Seminar 30. – 31.3.2004

  15. SEM image of reduced samples using 3000x magnification SEM image (3000x) of an un-doped sample after reduction. SEM image (3000x) of a doped sample (+3.78 wt. % Al2O3) after reduction. Blast Furnace Seminar 30. – 31.3.2004

  16. SEM image of reduced samples using 6000x magnification SEM image (6000x) of an un-doped sample after reduction. SEM image (6000x) of a doped sample (+3.78 wt. % Al2O3) after reduction. Blast Furnace Seminar 30. – 31.3.2004

  17. ▬ +3.78 wt. % Al2O3 ▬ +0 wt. % Al2O3 Experiments interrupted after 30 minute reduction Blast Furnace Seminar 30. – 31.3.2004

  18. SEM images from reduced briquettes interrupted after 30 minutes reduction Magnification 250X Magnification 3000X Magnification 10000X + 0 wt.% Al2O3 + 3.78 wt.% Al2O3 Blast Furnace Seminar 30. – 31.3.2004

  19. SEM-EDS analysis from sample interrupted after 30 minutes redution Magnification 10000X Blast Furnace Seminar 30. – 31.3.2004

  20. Reduction ”front” inside grains Reduction along lattice planes SEM image (+3.78 wt. % Al2O3) after 30 minutes reduction. (1000x) SEM image (+3.78 wt. % Al2O3) after 30 minutes reduction. (3000x) Blast Furnace Seminar 30. – 31.3.2004

  21. Blast Furnace Seminar 30. – 31.3.2004

  22. Stepwise reduction of alumina-bearing magnetite described with scanning electron microscope Blast Furnace Seminar 30. – 31.3.2004

  23. Stepwise reduction of alumina-bearing magnetite to wüstite schematically described Blast Furnace Seminar 30. – 31.3.2004

  24. Conclusion • Reduction was promoted by alumina • Disintegration of iron oxide structure associated with magnetite-wüstite phase transformation • Microscopic reduction front is not able to achieve but reduction goes along lattice planes Blast Furnace Seminar 30. – 31.3.2004

  25. THANK YOU FOR ATTENTION Blast Furnace Seminar 30. – 31.3.2004

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