A study on processing of blast furnace dust and sludge using reduction roasting and magnetic separation

Abstract

Blast furnace dust and sludge are by-products of ironmaking that contain high levels of iron and carbon, along with zinc. The increased zinc content complicates their recycling in the sintering and blast furnace processes, leading to their accumulation in waste dumps. This study investigates different treatment methods for recovering valuable elements from blast furnace dust (BFD) and blast furnace sludge (BFS) through reduction roasting and magnetic separation. Thermodynamic calculations and laboratory experiments were conducted to evaluate three approaches: magnetic separation without the roasting, as well as roasting stages to reduce iron to magnetite at 800 °C or metallic iron at 1200 °C, respectively. Direct magnetic separation without roasting and with the preliminary roasting at 800 °C resulted in magnetic concentrates of 49 – 63 % Fe from the BFD and BFS samples, but with elevated zinc content. The best results were achieved using reduction roasting at 1200 °C for 120 min, followed by grinding the samples to –0.054 mm and magnetic separation with a magnetic field of 0.1 T. As a result, the metallized magnetic concentrate containing 73.8 % Fe and 0.048 % Zn was obtained from the BFS sample (initially containing 39.5 % Fe and 0.31 % Zn), while a concentrate containing 80 % Fe and 0.019 % Zn was produced from the BFD sample (initially containing 44.6 % Fe and 0.31 % Zn). The iron recovery into the concentrates for the BFS and BFD samples was 92.8 and 89.7 %, respectively. The proposed approach can produce valuable materials for ferrous and non-ferrous metallurgy from these by-products, increase the efficiency of sintering and blast furnace processes, and reduce waste accumulation.