Reduction and consolidation mechanisms of chromite pellets during pre-reduction

The shaft furnace pre-reduction of chromite pellets may offer a cost-effective alternative to the capital-intensive grate-kiln system for ferrochrome production. This study investigated the temperature-dependent reduction and consolidation behaviour under simplified shaft-furnace-oriented conditions in a high-temperature tube furnace. Using a coke reductant (C/O molar ratio = 0.8) under an argon atmosphere, we evaluated the effects of temperature (1000–1400°C) on reduction degree and crushing strength of pellets. At 1300°C, the pellets simultaneously achieved a high reduction degree of 66.23% and a cold crushing strength of 864.6 N, thereby meeting the stringent feed requirements for submerged arc furnaces (SAFs). Microstructural characterisation revealed that the strength enhancement was linked to the formation of a continuous metallic iron network and subsequently to an FeCr alloy. The reduction mechanism proceeded through three distinct stages: initial pore formation via O2− removal, growth of a metallic iron layer, and final chromium reduction. The last stage was governed by solid-state diffusion of Fe2+, Cr3+, and O2− ions after the dense product layer formed. These results clarify the micro-mechanisms controlling pellet quality and provide a basis for further assessment of shaft-furnace-oriented chromite pellet pre-reduction.