Interactions between the gas phase in a nickel flash smelting furnace and the refractory lining

Magnesia (MgO)-chromite (MgCr₂O₄) spinel-based refractories are applied as lining materials in copper and nickel flash smelting furnaces due to their excellent durability against thermal shocks, heat, and melt erosion forces. In smelters, the refractories experience high temperatures but also thermal gradients due to the cooling of the walls. In addition, the refractories are subjected to an aggressive gaseous environment on the gas-space side with more than 40 vol.% of SO₂. For optimal lining performance, more light needs to be shed on the interactions between the refractory and the smelter atmosphere, for example, the reaction mechanisms of refractory wear need to be understood. This work analyzed and compared the unused and reacted genuine refractories from a nickel flash smelting furnace to identify the reactive species and define the reaction mechanisms. The characterization was carried out with SEM-EDS, μ-CT, and XRD. The unused magnesia-chromite refractory had a two-phase microstructure consisting of MgO and (Fe,Mg)(Al,Cr)₂O₄ spinel. Compared to the unused material, the reacted refractory was denser and contained several zones with dissimilar chemical compositions, likely driven by the thermal gradient. For example, the hot zone of the refractory was depleted in MgO, whereas sulfur-containing species were identified deeper in the material, towards the cooled external wall of the smelter. Furthermore, the thermal gradient affected the inward diffusion of gaseous chemical species from the flash-smelting process, enabling their reaction with some refractory constituents. Interactions with slag revealed slight dissolution and the formation of silicates. The results from the microstructural characterization of the refractories will be presented and discussed. The results lay the basis for future activities: controlled lab-scale experiments and computational modeling of refractory behavior.