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

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.