Zinc Enrichment in In-Plant Electrostatic Precipitator Dust Recycling by Air Classification in Converter Steelmaking.

Steelmaking in a basic oxygen furnace generates a considerable amount of dust, which is separated in a growing number of plants by dry de-dusting systems. This dust is rich in Fe and therefore, suitable for recycling within the steel mill. Because of the elevated Zn content recycling via the sintering process is often not feasible. Therefore, several steel mills apply in-plant dust recycling where the dust is recycled back into the furnace. Thereby, the Zn content of the dust increases steadily until the desired concentration in the dust for discharge is reached. In this procedure, the Zn atoms in the dust are circulated several times consuming energy and reduction agent for the volatilization each time. Classification experiments with basic oxygen furnace dust performed in this study show a certain dependence of the Zn concentration on the particles size. This size dependence is exploited by introducing an air classification step into the recycling process. The calculations for this novel process show that the required average number of times a Zn atom has to be volatilized and can be reduced by 35–72% depending on the underlying circumstances. Thus, the energy and reduction agent consumption required for dust recycling can be reduced substantially.