Diffusion and reaction mechanism of limestone and quartz in fluxed iron ore pellet roasting process

Abstract

The increase to the proportion of fluxed pellets in the blast furnace burden is a useful way to reduce the carbon emissions in the ironmaking process. In this study, the interaction between calcium carbonate and iron ore powder and the mineralization mechanism of fluxed iron ore pellet in the roasting process were investigated through diffusion couple experiments. Scanning electron microscopy with energy dispersive spectroscopy was used to study the elements’ diffusion and phase transformation during the roasting process. The results indicated that limestone decomposed into calcium oxide, and magnetite was oxidized to hematite at the early stage of preheating. With the increase in roasting temperature, the diffusion rate of Fe and Ca was obviously accelerated, while the diffusion rate of Si was relatively slow. The order of magnitude of interdiffusion coefficient of Fe₂O₃–CaO diffusion couple was 10⁻¹⁰ m²·s⁻¹ at a roasting temperature of 1200°C for 9 h. Ca₂Fe₂O₅ was the initial product in the Fe₂O₃–CaO–SiO₂ diffusion interface, and then Ca₂Fe₂O₅ continued to react with Fe₂O₃ to form CaFe₂O₄. With the expansion of the diffusion region, the sillico-ferrite of calcium liquid phase was produced due to the melting of SiO₂ into CaFe₂O₄, which can strengthen the consolidation of fluxed pellets. Furthermore, andradite would be formed around a small part of quartz particles, which is also conducive to the consolidation of fluxed pellets. In addition, the principle diagram of limestone and quartz diffusion reaction in the process of fluxed pellet roasting was discussed.

Keywords

fluxed iron ore pellet / limestone / hematite / quartz / diffusion reaction

References

[[1]] Zhang F, Zhu DQ, Pan J, Guo ZQ, Yang CC. Effect of basicity on the structure characteristics of chromium-nickel bearing iron ore pellets. Powder Technol., 2019, 342: 409,

[[2]] B. Hu, P.W. Hu, B. Lu, et al., NO_x emission reduction by advanced reburning in grate-rotary kiln for the iron ore pelletizing production, Processes, 8(2020), No. 11, art. No. 1470.

[[3]] Guo YF, Liu K, Chen F, et al.. Effect of basicity on the reduction swelling behavior and mechanism of limestone fluxed iron ore pellets. Powder Technol., 2021, 393: 291,

[[4]] Wang P, Wang CQ, Wang HT, Long HM, Zhou TB. Effects of SiO₂, CaO and basicity on reduction behaviors and swelling properties of fluxed pellet at different stages. Powder Technol., 2022, 396: 477,

[[5]] Lv W, Sun ZQ, Su ZJ. Life cycle energy consumption and greenhouse gas emissions of iron pelletizing process in China, a case study. J. Clean. Prod., 2019, 233: 1314,

[[6]] Lu JG, Lan CC, Lyu Q, Zhang SH, Sun JN. Effects of SiO₂ on the preparation and metallurgical properties of acid oxidized pellets. Int. J. Miner. Metall. Mater., 2021, 28(4): 629,

[[7]] Wang HT, Sohn HY. Effect of CaO and SiO₂ on swelling and iron whisker formation during reduction of iron oxide compact. Ironmaking Steelmaking, 2011, 38(6): 447,

[[8]] Zhang GC, Luo GP, Sun CC. Effect of CaF₂ on the reduction swelling properties of iron ore briquettes in different reduction stages. Min. Metall. Explor., 2021, 38(4): 1711

[[9]] Umadevi T, Kumar A, Karthik P, Srinidhi R, Manjini S. Characterisation studies on swelling behaviour of iron ore pellets. Ironmaking Steelmaking, 2018, 45(2): 157,

[[10]] Shaik MB, Sekhar C, Dwarapudi S, et al.. Characterization of colemanite and its effect on cold compressive strength and swelling index of iron ore pellets. Min. Metall. Explor., 2021, 38(1): 217

[[11]] Dishwar RK, Mandal AK, Sinha OP. Studies on highly fluxed iron ore pellets hardened at 1100°C to 1200°C. Metall. Mater. Trans. B, 2019, 50(2): 617,

[[12]] R.K. Dishwar and O.P. Sinha, Effect of basicity on the activation energy during reduction of highly fluxed iron ore pellets, Fuel, 296(2021), art. No. 120640.

[[13]] Wang S, Guo YF, Fan JJ, et al.. Degradation mechanism of high alumina refractory bricks by reaction with deposits in a rotary kiln for fluxed iron ore pellets production. Ceram. Int., 2022, 48(9): 12014,

[[14]] Bai KK, Liu LC, Pan YZ, Zuo HB, Wang JS, Xue QG. A review: Research progress of flux pellets and their application in China. Ironmaking Steelmaking, 2021, 48: 1048,

[[15]] Dwarapudi S, Ghosh TK, Tathavadkar V, Denys MB, Bhattacharjee D, Venugopal R. Effect of MgO in the form of magnesite on the quality and microstructure of hematite pellets. Int. J. Miner. Process., 2012, 112–113: 55,

[[16]] Iljana M, Kemppainen A, Paananen T, et al.. Effect of adding limestone on the metallurgical properties of iron ore pellets. Int. J. Miner. Process., 2015, 141: 34,

[[17]] Dwarapudi S, Sekhar C, Paul I, Prasad YGS, Modi K, Chakraborty U. Effect of fluxing agents on reduction degradation behaviour of hematite pellets. Ironmaking Steelmaking, 2016, 43(3): 180,

[[18]] Wang RR, Zhang JL, Liu ZJ, Liu XL, Xu CY, Li Y. Effects of magnesium olivine on the mineral structure and compressive strength of pellets. Ironmaking Steelmaking, 2020, 47(2): 100,

[[19]] Prusti P, Barik K, Dash N, Biswal SK, Meikap BC. Effect of limestone and dolomite flux on the quality of pellets using high LOI iron ore. Powder Technol., 2021, 379: 154,

[[20]] Dwarapudi S, Ghosh TK, Shankar A, Tathavadkar V, Bhattacharjee D, Venugopal R. Effect of pellet basicity and MgO content on the quality and microstructure of hematite pellets. Int. J. Miner. Process., 2011, 99(1–4): 43,

[[21]] Meraj M, Pramanik S, Pal J. Role of MgO and its different minerals on properties of iron ore pellet. Trans. Indian Inst. Met., 2016, 69(6): 1141,

[[22]] Dwarapudi S, Banerjee PK, Chaudhary P, et al.. Effect of fluxing agents on the swelling behavior of hematite pellets. Int. J. Miner. Process., 2014, 126: 76,

[[23]] Prusti P, Barik K. Effect of additives concentration on pelletization of high grade hematite. Mater. Today Proc., 2020, 33: 5373,

[[24]] Zhang YB, Chen XJ, Su ZJ, et al.. Improving properties of fluxed iron ore pellets with high-silica by regulating liquid phase. J. Iron Steel Res. Int., 2022, 29(9): 1381,

[[25]] Kemppainen A, Ohno KI, Iljana M, et al.. Softening behaviors of acid and olivine fluxed iron ore pellets in the cohesive zone of a blast furnace. ISIJ Int., 2015, 55(10): 2039,

[[26]] Wang RR, Zhang JL, Liu ZJ, Li Y, Xu CY. Effect of CaO and MgO additives on the compressive strength of pellets: Exploration on the decisive stage during induration. Powder Technol., 2021, 390: 496,

[[27]] Firth AR, Garden JF, Douglas JD. Phase equilibria and slag formation in the magnetite core of fluxed iron ore pellets. ISIJ Int., 2008, 48(11): 1485,

[[28]] Feng GS, Wu SL, Han HL, Ma LW, Jiang WZ, Liu XQ. Sintering characteristics of fluxes and their structure optimization. Int. J. Miner. Metall. Mater., 2011, 18(3): 270,

[[29]] Kongoli F, Mcbow I, Budd R, Llubani S, Yazawa A. Effect of oxygen potential and fluxing components on phase relations during sintering of iron ore. J. Min. Metall. Sect. B Metall., 2010, 46(2): 123,

[[30]] Li HB, Pinson DJ, Zulli P, et al.. Interaction between mineral phases in a hematite iron ore and fluxing materials during sintering. Metall. Mater. Trans. B, 2021, 52(1): 267,

[[31]] Ding X, Guo XM. Study of SiO₂ involved in the formation process of silico-ferrite of calcium (SFC) by solid-state reactions. Int. J. Miner. Process., 2016, 149: 69,

[[32]] Ding X, Wang YJ, Guo XM, Ran SL, Ma CY. Investigation of structural and electrical properties of silico-ferrite of calcium (SFC) in the Fe₂O₃-CaO-SiO₂ system synthesized by solid-state reaction. J. Mater. Sci. Mater. Electron., 2019, 30(16): 15715,

[[33]] Ding X, Guo XM. The sintering characteristics of mixing SiO₂ with calcium ferrite at 1473 K (1200°C). Metall. Mater. Trans. B, 2015, 46(4): 1742,

[[34]] Wang HR, Kou R, Harrington T, Vecchio KS. Electromigration effect in Fe-Al diffusion couples with field-assisted sintering. Acta Mater., 2020, 186: 631,

[[35]] Wen J, Sun HY, Jiang T, Chen BJ, Li FF, Liu MX. Comparison of the interface reaction behaviors of CaO–V₂O₅ and MnO₂–V₂O₅ solid-state systems based on the diffusion couple method. Int. J. Miner. Metall. Mater., 2023, 30(5): 834,

[[36]] Wei W, Yue HR, Xue XX. Diffusion coefficient of Ti⁴⁺ in calcium ferrite/calcium titanate diffusion couple. Int. J. Miner. Metall. Mater., 2020, 27(9): 1216,

[[37]] Wang RR, Zhang JL, Liu ZJ, Liu XL, Xu CY, Li Y. Interaction between iron ore and magnesium additives during induration process of pellets. Powder Technol., 2020, 361: 894,

[[38]] Gao QJ, Shen YS, Wei G, Jiang X, Shen FM. Diffusion behavior and distribution regulation of MgO in MgO-bearing pellets. Int. J. Miner. Metall. Mater., 2016, 23(9): 1011,

[[39]] Fukuyama H, Hossain K, Nagata K. Solid-state reaction kinetics of the system CaO–FeO. Metall. Mater. Trans. B, 2002, 33(2): 257,

[[40]] Freer R. Self-diffusion and impurity diffusion in oxides. J. Mater. Sci., 1980, 15(4): 803,

[[41]] Jeon JW, Jung SM, Sasaki Y. Formation of calcium ferrites under controlled oxygen potentials at 1273 K. ISIJ Int., 2010, 50(8): 1064,