Effect of Calcium Oxide on the Structure and the Thermal Properties of Granulated High-Iron Slags

The effect of calcium oxide (3.5–11.1%) on the microstructure, the elemental composition, and the microhardness of the phases that form during the water granulation of the molten slags having formed in autogenous smelting of copper–zinc concentrates is studied by metallography, X-ray diffraction, and electron-probe microanalysis. The slag granulation leads to the formation of an amorphous component, the amount of which decreases with increasing calcium oxide content. Copper, lead, and arsenic in the slags are mainly in the form of sulfide inclusions, and zinc is present in both sulfides and oxides. The introduction of calcium oxide in the slags (up to 11.1%) promotes coarsening of sulfide inclusions and an increase in the microhardness of the silicate phases. Differential scanning calorimetry is used to determine the thermal properties of the slags, namely, the temperatures and heats of devitrification, “cold crystallization” of amorphous phases, melting, and solidification. The results obtained can be used to choose slag cooling conditions and to prepare slags for the extraction of valuable metals by beneficiation methods.