High-temperature hydrogen pre-reduction of oxidatively sintered chromite pellets and its implications for downstream ferrochrome production

Abstract

• H2 pre-reduction reached Fe and Cr metallization of 93.3 and 18.8%, respectively. • Cr metallization remained low due to the hindering effect of H2O. • More H2 is needed to reduced Fe2O3 than for FeO. • CO emissions can be reduced by 50.4% if ore is pre-reduced using H2. This study investigated the high-temperature hydrogen (H 2 ) pre-reduction of oxidatively sintered chromite pellets to reduce the carbon (C) dependence during downstream ferrochrome (FeCr) production. The pellets, obtained from a South African sinter plant, were subjected to reduction temperatures and times of 1400 – 1630°C and 15 – 120 min, respectively. Iron (Fe) and chromium (Cr) metallization peaked at 93.3% and 18.8%, respectively, for samples reduced at 1460°C for 120 min. XRD showed that the as-received pellets encompassed mainly chromite and a sesquioxide phase, which is associated with oxidized chromite. SEM showed that the metallized phases that formed after H 2 reduction occurred as finely distributed phases within the chromite particle interiors, which is typical for the H 2 reduction of pre-oxidized chromite. This observation suggests that H 2 could penetrate the particles, and that reduction was not localized at the particle edges. Prolonged H 2 reduction transformed the finely distributed metallic phases into larger conglomerates, concentrated at the chromite particle surfaces. A theoretical process flow showed that the H 2 required for reduction is determined by the form of Fe present in the ore. Specifically, the power required to generate the needed H 2 to reduce Fe-oxides present per ton of chromite is 271.9 and 395.4 kWh if Fe occurs as FeO and Fe 2 O 3 , respectively.