Effect of Basicity on Reduction Swelling of Bayan Obo Iron Ore Pellets: XRD and Mössbauer Analysis

The high proportion of pelletizing blast furnace smelting technology is one of the important means to achieve the goal of “Double Carbon”. Pellets prepared from Bayan Obo iron ore concentrate were selected as the research object. An X-ray diffractometer (XRD) and a Mössbauer spectrometer were used to analyze the influence mechanism of basicity on the reduction swelling performance of the pellets. The results showed that, when the basicity was 0.8, the reduction swelling index (RSI) of the pellets was the largest, and the lattice constant (a), grain size (L_c), average stacking layers of grain (N_ave), residual stress (ε), and crystallinity of pellet reduction products reached extreme values. With the progress of the reduction reaction, ε, of the pellets gradually increased, and then decreased sharply in the third reduction stage. The crystallinity gradually decreased with the reduction reaction, indicating the amounts of K, Na, and Ca entering the iron oxide lattice. A smaller binding energy, larger space of motion, larger distortions, and residual stress are the reasons for the high RSI of the pellets. The Fe(II) of the pellets in the octahedral void was seriously absent, and the absence of Fe(II) gradually increased with the increase of basicity. Fe in pellets with a basicity of 0.8 has a lower coordination number and a smaller atomic arrangement.