Feasibility of air classification in dust recycling in the iron and steel industry

The potential of air classification of dusts from dry off-gas cleaning for improved recycling of these dusts is investigated. By air classification, a dust can be separated into a coarse fraction and a fine fraction. Some components which are usually unwanted in recycled dust like alkali chlorides and Zn and Pb are often enriched in the fine dust fraction. Thus, air classification of dust before recycling will allow recycling of an increased amount of dust and, thereby reduce the amount of dust which has to be sent to landfill. The feasibility of such treatment is studied on the basis of estimated investment costs and operating costs. The main factors affecting the feasibility of such a treatment are the capacity of the unit, the cost of landfill of the respective dust, and the fraction of dust which can additionally be recycled after the treatment. The investigation of classification of BF dusts and sinter plant dust shows that economic operation can be reached under the assumed conditions at landfill costs above 35–60 EUR/t for BF dust and 90 EUR/t for sinter plant dry desulfurization and de-dusting residue. The integration of air classification into EAF dust in-plant recycling can be feasible, too.