Oxidation consolidation characteristics of chromite pellets during the roasting process

The roasting consolidation characteristics of chromite pellets were systematically studied in this paper. The results show that preheating time has little effect on the compressive strength of preheating chromite pellets. Under the appropriate preheating time of 10 min,increasing the preheating temperature can improve the compressive strength and oxidation rate of preheating chromite pellets linearly. The appropriate preheating temperature is 1050℃,at which the compressive strength of preheating chromite pellets can reach more than 400 N. In addition,compared with conventional iron ore pellets,a higher roasting temperature is required for chromite pellets. The compressive strength of chromite pellets increases from 1078 N to 1973 N when the roasting temperature increases from 1250℃ to 1350℃. During the preheating and roasting of chromite pellets,(Fe,Mg)(Cr,Fe,Al)₂O₄ is oxidized into(Fe,Mg)(Cr,Fe,Al)₂O₄ and(Cr,Fe,Al)₂O₃. The new phase(Cr,Fe,Al)₂O₃ is obviously generated when the temperature surpasses 1000℃.(Cr,Fe,Al)₂O₃ mainly distributes in the outer layer of the particles in a ring shape,while the acicular(Cr,Fe,Al)₂O₃ interlaces together with(Fe,Mg)(Cr,Fe,Al)₂O₄ in the internal part. Decreasing the Cr/Fe ratio in the raw ore concentrate or increasing the roasting temperature can facilitate the aggregation of(Cr,Fe,Al)₂O₃ around the outer layer of the particles,which in terms assists in the pellet consolidation and then enhances the compressive strength of chromite pellets.