Iron extraction from copper slag by additive-free activation roasting-magnetic separation

Abstract

Iron grain growth during deep reduction roasting is important for iron enrichment from copper slag (CS) through magnetic separation. In this work, a novel method of additive-free activation roasting, including oxidation and subsequent reduction roasting, was proposed to increase the iron grain size, then the iron was extracted by magnetic separation. The phase transformation of CS during activation roasting was studied by TG, XRD, SEM, and EDS. Results showed that the main mineral of fayalite in CS was decomposed into iron oxides and silica during oxidation roasting, and the thickness of iron oxide layer on the particle surface increased with the oxidation temperature. During reduction roasting, the CS and oxidized copper slag (OCS) were ultimately converted into metallic iron and cristobalite solid solution. In the reduced product obtained at 1150 °C, the iron grain sizes were 6.42 μm and 16.62 μm from CS and OCS-1100 °C, respectively. Furthermore, the Fe content in the magnetic concentrate was 72.86 % in the reduced product of CS while that was 87.85 % in the reduced product of OCS-1100 °C with an Fe recovery of ∼ 85 %. This study opens a new direction for iron enrichment from copper slag.