Removal Mechanism of Zn, Pb and Alkalis from Metallurgical Dusts in Direct Reduction Process

The high-temperature tube furnace was applied to simulate the rotary hearth furnace (RHF) for the direct reduction of zinc-bearing dusts from steel plants. The removal mechanism of Zn, Pb and alkalis from cold bonded briquettes made by mixing metallurgical wastes, such as dust from bag house filter, OG sludge, fine converter ash and dust from the third electric field precipitator of the sinter strand, in various proportions was investigated. More than 70% of metallization rate, more than 95% of zinc removal rate, 80% of lead removal, as well as more than 80% of K and Na removal rates were achieved for the briquettes kept at 1473–1603 K for 15 min during the direct reduction process respectively. The soot generated in the direct reduction process was studied by chromatography, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results suggested that the main phases of the soot were ZnO, KCl, NaCl and 4ZnO · ZnCl2 · 5H2O. Furthermore, the content of Zn reached 64.2%, which could be used as secondary resources for zinc making. It was concluded that KCl and NaCl in secondary dust resulted from the volatilization from the briquettes, whilst ZnO and PbO were produced by the oxidation of Zn or lead vapour from briquettes by direct reduction.