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基于原料特性互补的红土镍矿球团富氢还原行为调控

Hydrogen-rich reduction behavior regulation of lateritic nickel ore pellets based on raw material property complementarity

  • 摘要: 为阐明不同类型低品位红土镍矿的原料特性互补机制对复合球团的富氢还原行为的影响,以褐铁型(limonite,HT)、过渡型(germination,GD)和腐殖土型(humicite,FZ)红土镍矿氧化球团为对象,开展单矿球团和复合球团在不同还原气氛及温度下的还原性试验,并结合X射线衍射和扫描电子显微镜-能谱分析揭示其物相转变与微观结构演变行为。结果表明,3种单矿球团还原行为差异明显,HT型球团因铁氧化物含量较高、硅镁稳定相含量较低,还原速率最快,30 min还原度达到86%,120 min时接近完全还原;GD型球团受高SiO2、MgO组分及镁硅酸盐、尖晶石相限制,120 min还原度仅为72%;FZ型球团还原程度介于两者之间。复合配矿能够改善球团还原过程,在FZ型矿质量分数固定为30%的条件下,B2球团(HT型、GD型、FZ型质量分数比为20%∶50%∶30%)兼具较快初期还原速率和较高中后期还原度,60 min还原度达到87%。提高H2体积分数和还原温度均可促进铁、镍氧化物还原,使金属铁衍射峰增强、铁镍金属相增多并推动还原界面向内部迁移。富氢还原过程表现为表层优先还原、反应界面内移和后期扩散阻力增强,残余硅镁酸盐及尖晶石相包裹未还原基体,这是限制内部区域深度还原的重要原因。

     

    Abstract: To elucidate the influence of the complementary characteristics of different types of low-grade lateritic nickel ore on the hydrogen-rich reduction behavior of composite pellets, oxidized pellets of limonite (HT), germination (GD), and humicite (FZ) lateritic nickel ore were selected as research objects. Reduction tests were conducted on single-ore pellets and composite pellets under different reducing atmospheres and temperatures. X-ray diffraction and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analyses were used to reveal their phase transformation and microstructure evolution. The results show that the reduction behaviors of the three types of single-ore pellets differed significantly. HT-type pellets, due to their higher iron oxide content and lower content of stable silica-magnesium phases, exhibit the fastest reduction rate, reaching reduction degree of 86% in 30 min and near-complete reduction in 120 min. GD-type pellets, limited by high SiO2 and MgO content and magnesium silicate and spinel phases, have a reduction rate of only 72% in 120 min. The reduction degree of FZ-type pellets fall between the two. Composite ore blending can improve the pellet reduction process. With a fixed FZ-type ore mass fraction of 30%, B2 pellets (HT-type, GD-type, FZ-type mass fraction ratio of 20%∶50%∶30%) exhibit both a faster initial reduction rate and a higher degree of reduction in the middle and later stages, reaching a reduction degree of 87% after 60 minutes. Increasing the H2 volume fraction and reduction temperature can promote the reduction of Fe and Ni oxides, resulting in enhanced diffraction peaks of metallic iron, an increase in the iron-nickel metallic phase, and a shift of the reduction interface inwards. The hydrogen-rich reduction process is characterized by preferential reduction at the surface, inward shift of the reaction interface, and enhanced diffusion resistance in the later stages. Residual magnesium silicate and spinel phases encapsulating the unreduced matrix are important factors limiting the depth of reduction in the internal regions.

     

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