The behavior of separation and enrichment of valuable metals during the synergistic processing of metallurgical dust and sludge via roasting in rotary kiln

The generation of ironmaking and steelmaking dust and sludge exceeds 100 million tons annually, and stacking critically pollutes the environment. The joint treatment of such wastes for recycling metals is a promising approach to resolving these problems. This study focused on the separation and enrichment of metals during the synergistic processing of blast furnace dust, electric arc furnace dust, and steel pickling sludge in a rotary kiln at high temperature. Research results indicate that Na2O, K2O, Rb2O, Cu2O, ZnO, CdO, PbO, Bi2O3, and Sb2O3 may be separated during roasting. Under optimized Zn removal conditions of 30 min roasting time and 1373 K roasting temperature, the removal percentages of Sn, Sb and Cu reach 91.9%, 97.2%, and 72.4%, respectively, while Bi, Rb and Cd are removed almost entirely from the mixture of dust and sludge. The removed metals condense before the flue gas outlet (330 K) and are concentrated in the Zn-rich powder. The concentrations of Sn, Sb, Bi, Rb, and Cd in the Zn-rich powder were 5-7 times those in the mixture. The synergistic treatment of metallurgical dust and sludge may facilitate the efficient separation and enrichment of certain valuable metals, and the methods may be extended to jointly processing the other solid wastes; however, HCl gas formation may complicate gas cleaning.