Effect of hydrogen pre-reduction on iron and chromium metallization of oxidatively sintered chromite pellets during subsequent carbothermic reduction

Hydrogen (H 2 ) pre-reduction was evaluated as a pre-treatment to improve iron (Fe) and chromium (Cr) metallization of oxidatively sintered chromite pellets during subsequent carbothermic reduction relevant to submerged arc furnace (SAF) smelting. Industrial Outotec-type pellets from two South African sinter plants were pre-reduced in H 2 at 1100 °C for 10–180 min and then reduced at 1300 °C for 60 min using either a carbon (C) bed (external contact) or C-blended (distributed contact) configuration. X-ray diffraction (XRD) showed that the plants’ pellets differed in initial oxidation state; more-oxidized pellets achieved higher Fe metallization in H 2 and higher Cr metallization during carbothermic reduction. After 180 min H 2 pre-reduction, Fe metallization was 60.9% (H 2 only), 60.1% (H 2 /C-bed), and 84.9% (H 2 /C-blended), with corresponding Cr metallization of < 1.0%, 3.0% and 59.1%. SEM–EDX identified Fe-rich and Cr-rich metallic phases after C-blended reduction, whereas H 2 and C-bed tests produced Fe and Fe-Cr phases, respectively. Mass-loss accounting suggested an estimated reduction of up to 36.8% in C-derived CO(g) generation compared with C-blended reduction without H 2 pre-reduction. The results indicate that selective Fe metallization during H 2 pre-reduction reduces competing carbon demand for Fe-oxide reduction, improving C utilization toward Cr 2 O 3 reduction during the C-blended step under non-melting conditions.