Application of air classification for improved recycling of sinter plant dust

In sinter plants the dust collected from the off-gas is recycled back to the feed material as long as the chloride content of this dust in below the plant-specific limits. To avoid an up-cycling of chloride in the system in many sinter plants the dust from the last field of the electrostatic precipitator is excluded from recycling since the chloride concentration is higher in the dust collected in the rear fields of the electrostatic precipitator. In this study the application of air classification is investigated to raise the dust recycling rate and/or to increase the chloride discharge. Samples from each field of the four field electrostatic precipitator of an iron ore sinter plant were classified and analyzed. The mass-recovery - chloride-removal functions for various classification variants were calculated by using approximation functions for the mass and the chloride content of the particle classes produced. The results show that in comparison with the actual situation where about 20% of the sintering dust which contains about 30% of the chloride is excluded from recycling, by applying air classification the recycling rate could be increased to about 95%, retaining the same chloride discharge rate. In the case of the expected extraction of potassium from sintering dust in the future, air classification could also be used to increase the potassium chloride concentration of the input material.