Removal of Zinc and Lead from Blast Furnace Dust in a Fluidized-Bed Roaster

Abstract

Industrial trials were carried out, using a fluidized-bed roaster, to investigate the effect of the roasting time, roasting temperature, basicity, and CaCl2 dose on the removal rates of Zn and Pb from blast furnace dust. Increasing the roasting time improved the Zn and Pb removal rates, and the maximum amounts of the Zn and Pb removal were achieved within the first 30 min. Increasing the roasting temperature favored the facile removal of both Zn and Pb, but the effect of the roasting temperature on Pb removal was more obvious than that on Zn removal. When CaCl2 is added, CaCl2 reacts with ZnO and PbO in the ore to form ZnCl2 and PbCl2, respectively. They are discharged along with sintering gas. Therefore, both the Zn and Pb removal rates improved evidently when CaCl2 was added, especially when the added amount of CaCl2 was in the range of 10–12%. Removal rates of up to 96% were achieved for Zn, while Pb removal rates of higher than 80% were achieved. During the sintering process, silicon and iron which are in the form of oxide negative ions will form complex compounds with zinc. This can make zinc removal difficult. If CaO is added as flux, the basicity increases and Ca replaces Zn, alleviating this problem of difficulty in Zn removal. Thus, upon increasing the basicity, the removal rate of Zn is improved, especially, increasing the basicity from 0.8 to 1.4 improved the Zn removal rate significantly.