The effect of hydrogen pre-reduction on the carbon-reducibility of pelletised UG2 chromite

Abstract

This study investigated the incorporation of hydrogen (H₂) as a partial replacement of carbon (C) during ferrochrome (FeCr) production. Chromite was subjected to H₂-reduction to metallise its iron (Fe) −oxide content, followed by the removal of the metallised Fe by acid leaching. Hereafter, the chromium (Cr) −oxide rich ore was subjected to C-reduction. During H₂-reduction, 64.3 % ± 6.1 % of Fe-oxides could be metallise, whereas C-reduction metallised the remaining Fe-oxides, as well as the Cr-oxide constituency. The C-reduction at 1300 °C resulted in near-complete metallisation of both the Fe- and Cr-oxide constituencies. By following this route, C emissions were reduced by approximately 16 %. It was further determined the process followed a shrinking core model. This model was confirmed by sub-surface microscopy, which highlighted the formation of a metallic layer at the chromite particle surface. This layer formation was evident during both H₂- and C-reduction. It was also found that during the implemented Fe removal process that decrepitation of the H₂-treated ore occurred. Mineralogical analysis of the H₂-reduced and leached chromite suggests the formation of an eskolaite-type phase. Subsequent removal of the metallised Cr resulted in a MgAl₂O₄ spinel-type phase, which suggests that the majority of Fe and Cr were removed. These findings provide comprehensive insights into the chemical, physical, and mineralogical transformations of chromite during reduction and leaching, offering valuable implications for the decarburisation of FeCr production.