The influence mechanism of basicity on the reduction swelling index (RSI) of iron ore briquettes was investigated using the SEM analysis and Factsage 7.3 thermodynamic calculations based on the addition of pure CaO to Bayan Obo iron concentrate. The results revealed that the solid solution of Ca 2+ in the FeO lattice increased with the basicity of the briquettes, whereas the diffusion channels of Fe 2+ ions increased during the reduction process from FeO to Fe and resulted in the formation of a great number of slender and anisotropic iron whiskers, which consequently increased the RSI. Furthermore, the melting point of the slag phase decreased as the CaO content increased; this reduced its ability to resist the reduction swelling of iron oxides. When the basicity was increased from 0.3 to 0.8, the RSI reached a maximum of 69.85%. However, due to the saturated solid solution of Ca 2+ in FeO lattice, as the basicity further increased from 0.8 to 1.2, excess CaO melting into the slag phase promoted the precipitation of spinel minerals with high melting points and difficult reduction properties. Thus, the diffusion of Fe 2+ and the growth of the iron whiskers were hindered, and the RSI was reduced.

中文翻译：

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碱度对铁矿石压块还原溶胀性能的影响

基于向白云鄂博铁精矿中添加纯 CaO，使用 SEM 分析和 Factsage 7.3 热力学计算研究了碱度对铁矿石压块还原膨胀指数 (RSI) 的影响机制。结果表明，随着团块碱度的增加，Ca 2+ 在 FeO 晶格中的固溶量增加，而 Fe 2+ 离子的扩散通道在从 FeO 到 Fe 的还原过程中增加，导致形成大量细长和各向异性的铁晶须，从而增加了 RSI。此外，随着CaO含量的增加，渣相的熔点降低；这降低了其抵抗氧化铁还原溶胀的能力。当碱度从 0.3 增加到 0.8 时，RSI 最高达到 69.85%。然而，由于Ca 2+ 在FeO晶格中饱和固溶，随着碱度从0.8进一步增加到1.2，过量的CaO熔入渣相促进了高熔点、难还原性尖晶石矿物的析出。因此，Fe 2+ 的扩散和铁晶须的生长受到阻碍，RSI 降低。