Probing study on separating Pb, Zn, and Fe from Lead slag by coal-based direct reduction

Abstract

Water-quenched lead slags are classified as hazardous materials because they contain a certain amount of heavy metals. In this study, coal-based direct reduction followed by magnetic separation was presented to separate Pb, Zn, and Fe from lead slag. Lead slag was mixed with coal and additive and treated in a laboratory tube furnace. In the process of direct reduction, Pb and Zn compounds were reduced to elementary substances and entered into flue gas as dust. Fe was reduced to metallic iron and separated from roasted slag by magnetic separation. The effects of roasting temperature, roasting time, and usage of coal and additive were experimentally determined. The following optimum process parameters were proposed: weight ratios of slag, coal ratio of 30%, additive ratio of 15%, and roasting at 1 200°C for 90 min. Under these conditions, a magnetic concentrate containing 93.73% total iron and recovery rate of 80.32% was obtained. In the process of direct reduction, the Pb and Zn volatilization rates were 97.48% and 97.19%, respectively. Lead slag and roasted slags were subjected to scanning electron microscopy and X-ray diffraction to identify the reduction mechanism of Pb, Zn, and Fe during direct reduction.