Gas-based reduction of vanadium titano-magnetite concentrate: behavior and mechanisms

The reduction of vanadium titano-magnetite pellets by H₂–CO at temperatures from 850 to 1050°C was investigated in this paper. The influences of pre-oxidation treatment, reduction temperature, and ({{{V_{{H_2}}}} mathord{left/{vphantom {{{V_{{H_2}}}} {left( {{V_{{H_2}}} + {V_{CO}}} right)}}} right.kern-nulldelimiterspace} {left( {{V_{{H_2}}} + {V_{CO}}} right)}}) on the metallization degree were studied. The results showed that pre-oxidation played a substantial role in the reduction of vanadium titano-magnetite pellets. During the reduction process, the metallization degree increased with increasing temperature and increasing ({{{V_{{H_2}}}} mathord{left/{vphantom {{{V_{{H_2}}}} {left( {{V_{{H_2}}} + {V_{CO}}} right)}}} right.kern-nulldelimiterspace} {left( {{V_{{H_2}}} + {V_{CO}}} right)}}). The phase transformation of pre-oxidized vanadium titano-magnetite pellets during the reduction process under an H₂ atmosphere and a CO atmosphere was discussed, and the reduced samples were analyzed by scanning electron microscopy (SEM) in conjunction with back scatter electron (BSE) imaging. The results show that the difference in thermodynamic reducing ability between H₂ and CO is not the only factor that leads to differences in the reduction results obtained using different atmospheres. Some of Fe_3?x Ti _x O₄ cannot be reduced under a CO atmosphere because of the densification of particles’ structure and because of the enrichment of Mg in unreacted cores. By contrast, a loose structure of particles was obtained when the pellets were reduced under an H₂ atmosphere and this structure decreased the resistance to gas diffusion. Moreover, the phenomenon of Mg enrichment in unreacted cores disappeared during H₂ reduction. Both the lower resistance to gas diffusion and the lack of Mg enrichment facilitated the reduction of vanadium titano-magnetite.