Recovery of iron and removal of hazardous elements from metallurgical slags

Jungho Heo, Prof. Dr. Joohyun Park

Novel aluminothermic smelting reduction (ASR) process was investigated for cleaning ferrous and non-ferrous slags; this process is not only able to recover valuable iron, but also eliminates hazardous elements from the end-of-life slag products. The effect of adding Al on the reduction of iron oxide and subsequent iron recovery from waste steel slag and copper slag at 1773 K was investigated using an induction furnace. The content of FeO and Al2O3 in the molten slag varied dramatically over a 5-min period, followed by nearly constant values. Iron recovery exhibited a maximum value at specific Al/FeO molar ratio. To determine the iron recovery, a novel triangular material balance diagram, which represents the balance among the reduced iron ingot, the reduced iron droplets dispersed in the slag phase, and the residual (unreduced) iron, was proposed. Solid compounds, such as spinel and olivine, were precipitated in the slag during the ASR process; this was confirmed by both XRD analysis and a thermochemical computation method. Finally, the elimination rate of hazardous elements, such as As, Bi, Pb, and Sb, from end-of-life copper slag by the ASR process was determined.