Potential of air classification for zinc management in dust recycling in ironmaking

The dusts generated in the blast furnace process are partly recycled via the sinter plant. The amount of Zn which is recycled with these dusts is limited to avoid operational problems. Usually, the dusts from the dust catcher and the cast house dust are recycled, while the residue from second stage top-gas de-dusting has to be discharged at least partly. In this study the application of air classification was investigated for maximization of the recycled fractions of the dusts at certain limits for the amount of recycled Zn. For this, approximation functions for the dependence of the Zn content in the coarse material on the fraction of the coarse material had to be derived from classification experiments. The calculations showed that the positive effect of air classification was higher at lower values of the limit for the amount of Zn recycled with the dust. Depending on the value of this limit the possible increase in dust recycling in comparison to classification of the second stage filter dust only ranged from 0.27 to 0.45 kg/t HM for air classification of second stage filter dust and cast house dust and from 0.35 to 0.79 kg/t HM for classification of all three dusts.