Coarse sludge (sample A) and fine sludge (sample B) from a Brazilian Linz–Donawitz—LD steelworks integrated plant was characterized. Chemical analysis determined high-level content of iron (51.54–77.53%) and lower grades of zinc (0.49–1.69%). XRD analysis permitted to observe various mineralogical phases, such as metallic iron, wustite, franklinite, magnetite, portlandite, periclase, calcite, calcium oxide, silicon, moissanite-2H, and srebrodolskite. Microscopic Optical and Scanning Electron Microscopic studies shown morphologies of these residues were made up of globular and skeletal aggregates of metallic iron intergrown with crystals of iron oxides, especially wustite and a significant presence of calcite and calcium oxide in spherical nodes having particle sizes between 0.12 and 0.15 mm. Scanning Electron Microscopy–Energy-Dispersive X-ray spectroscopy studies denoted significant content of Fe, O, and Ca in both samples. In addition, a thermogravimetric analysis by DTG–DSC–TG at 1000 °C exhibited a mass loss of 97.43% for sample A and 92.57% for sample B.