Low-temperature reduction disintegration behavior and mechanism of lump ore under hydrogen-rich gas-based reduction conditions

To address the potential issue of low-temperature reduction disintegration （LTD） caused by the use of lump ore in hydrogen rich gas-based reduction processes, this study systematically investigated the effects of reduction temperature （450-600 ℃） and reducing atmosphere φ（H₂）/φ（H₂+CO） is 0.6-1.0 on the low temperature reduction disintegration behavior of a typical iron ore lump. The disintegration mechanism was revealed by combining weight loss rate, reduction degree, X-ray diffraction （XRD）, and microstructural characterization. The results show that the reduction temperature is the dominant factor controlling the low temperature reduction disintegration behavior of lump ore. Within the range of 450-600 ℃, as the reduction temperature increases, the weight loss rate and reduction degree of lump ore gradually increase, but the low temperature reduction disintegration performance significantly deteriorates. Taking the atmosphere with φ（H₂）/φ（H₂+CO）=0.6 as an example, when the temperature increases from 450 ℃ to 600 ℃, the L_TD>6.3 index （the mass fraction of particles larger than 6.30 mm after the low temperature reduction disintegration test） decreases from 75.56% to 20.16%, while the severe disintegration index L_TD<0.5 （the mass fraction of particles smaller than 0.50 mm after the test） sharply increases from 5.08% to 23.05%. Increasing the H₂ proportion in the reducing gas promotes the reduction reaction and may shorten the stress accumulation stage caused by the prolonged coexistence of hematite and magnetite, thereby improving the disintegration performance of lump ore to a certain extent. Microstructural analysis indicates that the lump ore has a dense structure and low porosity, so the volumetric stress generated during the transformation from hematite to magnetite is difficult to release in time, leading to crack propagation along grain boundaries, pores, and pre existing defects. Dynamic evolution results at 550 ℃ further reveal that the low temperature reduction disintegration process of the lump ore can be divided into three stages, preferential reduction at the edge, inward advancement of the phase transformation interface, and crack penetration. The essence of low temperature reduction disintegration of lump ore lies in the dense matrix limiting the uniform penetration of reducing gas into the deep part, forming a non uniformly advancing phase transformation front. The stress concentration induced by phase transformation and the inward penetration of cracks constitute the fundamental causal mechanism leading to overall aligned cracking and structural instability of the lump ore. This study provides a theoretical basis for the rational use of lump ore and the optimization of burden structure under hydrogen rich reduction conditions.