Effect of magnesia on the compressive strength of pellets

Abstract

The compressive strength of MgO-fluxed pellets was investigated before and after they were reduced. The porosity and pore size of green pellets, product pellets, and reduced pellets were analyzed to clarify how MgO affects the strength of the pellets. Experimental results show that when the MgO-bearing flux content in the pellets increases from 0.0wt% to 2.0wt%, the compressive strength of the pellets at ambient temperature decreases, but the compressive strength of the pellets after reduction increases. Therefore, the compressive strength of the pellets after reduction exhibits no certain positive correlation with that before reduction. The porosity and pore size of all the pellets (with different MgO contents) increase when the pellets are reduced. However, the increase in porosity of the MgO-fluxed pellets is relatively smaller than that of the traditional non-MgO-fluxed pellets, and the pore size range of the MgO-fluxed pellets is relatively narrower. The reduction swelling index (RSI) is a key factor for governing the compressive strength of the reduced pellets. An approximately reversed linear relation can be concluded that the lower the RSI, the greater the compressive strength of the reduced pellets is.

Keywords

iron ore pellets / compressive strength / magnesia / ore reduction / swelling

References

[1] Gao QJ, Shen FM, Wei G, Jiang X, Zheng HY. Effects of MgO containing additive on low-temperature metallurgical properties of oxidized pellet. J. Iron Steel Res. Int., 2013, 20(7): 25.

[2] Fu JY, Zhu DQ. Basic Principles, Techniques and Equipment of the Iron Ore Oxidized Pellets, 2005, Changsha, Central South University Press, 336

[3] Shen FM, Gao QJ, Wei G, Ding ZM. Effect of MgO-bearing additive on metallurgical property of pellets. Asia Steel International Conference 2012, 2012 19

[4] Mu L, Jiang X, Gao QJ, Wei G, Shen FM. Effect of hydrogen addition on low temperature metallurgical property of sinter. J. Iron Steel Res. Int., 2012, 19(4): 6.

[5] Gao QJ, Wen QL, Wei G, Jiang X, Shen FM. Study on the effect of caustic calcined magnesite to quality of green-pellets. The 4th Australia-China-Japan Symposium on Iron and Steelmaking, 2012 102

[6] Shen FM, Wu GS, Jiang X, Wei G, Li XG, Shen YS. Proper MgO addition in blast furnace operation. ISIJ Int., 2006, 46(1): 65.

[7] Zhou GF, Yang F. Effects of adding MgO on pelletizing ability and strength of pellet. Res. Iron Steel, 2009, 37(2): 10

[8] Biswas AK. Principles of Blast Furnace Ironmaking-Theory and Practice, 1981, Brisbane, Cootha Publishing House, 38

[9] Chun TJ, Zhu DQ, Pan J. Influence of sulfur content in raw materials on oxidized pellets. J. Cent. South Univ. Technol., 2011, 18(6): 1924.

[10] Semberg P, Andersson C, Björkman B. Interaction between iron oxides and olivine in magnetite pellets during reduction to wustite at temperatures of 1000–1300°C. ISIJ Int., 2013, 53(3): 391.

[11] Khaki JV, Kashiwaya Y, Ishii K. High temperature behaviour of selffluxed pellets during heating up reduction. Ironmaking Steelmaking, 1994, 21(1): 56

[12] Shen FM, Wu GS, Jiang X. A new process of proper MgO addition in blast furnace operation. Proceedings of Commemorative International Symposium on Ironmaking Process and Environment, 2005 25

[13] Coetsee T, Pistorius PC, de Villiers EE. Rate-determining steps for reduction in magnetite-coal pellets. Miner. Eng., 2002, 15(11): 919.

[14] Jiang X, Wu GS, Li GS, Shen FM. Study on improving the softening-melting properties of MgO-bearing iron ores. J. Northeast. Univ. Nat. Sci., 2007, 28(3): 365

[15] Matsumura M, Hoshi M, Kawaguchi T. Improvement of sinter softening property and reducibility by controlling chemical compositions. ISIJ Int., 2005, 45(4): 594.

[16] Pal J, Ghorai S, Goswami MC, Ghosh D, Bandyopadhyay D, Ghosh S. Behavior of fluxed lime iron oxide pellets in hot metal bath during melting and refining. Int. J. Miner. Metall. Mater., 2013, 20(4): 329.

[17] Suresh S. Fatigue of Materials, 1998, New York, Cambridge University Press, 70.

[18] Gao QJ, Wei G, He YB, Shen FM. Effect of MgO on compressive strength of pellet. J. Northeast. Univ. Nat. Sci., 2013, 34(1): 103

[19] Gao QJ, Jiang X, Wei G, Shen FM. Characterization of consolidation degree of iron ore pellet by mercury injection method. J. Northeast. Univ. Nat. Sci., 2013, 34(6): 832

[20] Gibson LJ, Ashby MF. Cellular Solids Structure and Properties, 1997, Cambridge, Cambridge University Press, 150

[21] Kemppainen A, Mattila O, Heikkinen EP, Paananen T, Fabritius T. Effect of H₂-H₂O on the reduction of olivine pellets in CO-CO₂ Gas. ISIJ Int., 2012, 52(11): 1973.

[22] Bao YW, Jin ZZ. Size effects and a mean-strength criterion for ceramics. Fatingue Fract. Eng. Mater. Struct., 1993, 16(8): 829.

[23] China Metallurgical Construction Association. Code for Design of Iron Pelletizing Engineering, 2009, Beijing, China Panning Press, 14