Recovery of iron and removal of hazardous elements from waste copper slag via a novel aluminothermic smelting reduction (ASR) process

Abstract

A novel aluminothermic smelting reduction (ASR) process was investigated for cleaning waste copper slag; this process is not only able to recover valuable iron, but also eliminates hazardous elements from the end-of-life slag product. The effect of adding Al on the reduction of iron oxide and subsequent iron recovery from waste copper slag at 1773 K was investigated by considering the thermophysical properties of the slag. The content of FeO and Al2O3 in the molten slag varied dramatically over a 5-min period, followed by nearly constant values. Because the reaction area and volume could not be determined (due to the explosive reaction characteristics of the ASR process), the apparent rate constant was employed for kinetic analysis. Iron recovery exhibited a maximum value at Al/FeO = 0.53. 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. Furthermore, the reaction mechanism between iron oxide and Al particles was newly proposed; this was based on systematic experimental observations. 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.