Degradation Mechanisms of the Magnesia-chromite Refractory Lining of Secondary Copper Smelters

During the smelting process of secondary raw materials, ZnO-containing fayalite (ZFS) slags can be generated in copper smelters. ZnO changes both the physical and chemical properties of the slag, which can consequently influence the corrosion behaviour of the refractory lining of the copper smelter. Besides ZnO, the levels of FeO and CaO in such fayalite-based slags need to be adjusted to meet the operation requirements during copper smelting, which consequently influence the properties of the slags. Therefore, the impact of the slag composition variation on the refractory lining of a secondary copper smelter was systematically investigated by lab scale tests in this work. For this, both rotating finger tests and crucible tests were performed using either the direct-bonded magnesia-chromite refractory (as industrially applied) or pure MgO (as this phase in the refractory is more severely attacked by the slag than the chromite). The slag composition was modified by varying ZnO contents from 0, 10 to 20 wt%, the FeO/SiO2 ratio from 0.4, 1.0, 1.4 to 1.8 and the CaO/SiO2 ratio from 0.04, 0.07, 0.12, 0.24 to 0.34. From the microstructural and compositional analyses, it is concluded that within the tested range, ZnO has a similar role as FeO and no additional degradation mechanisms are introduced. For high ZnO containing slags (i.e. 20 wt% ZnO), the MgO solubility is minimal at a ratio of FeO/SiO2 of 1.7 (for CaO/SiO2 = 0.04), whereas it continuously increases with augmenting CaO/SiO2 ratios (for FeO/SiO2 = 1.4). Based on the identified degradation mechanisms, a next series of lab scale tests with a high ZnO content (20 wt% ZnO) slag was designed to evaluate the effect of temperature, refractory type and a prior infiltration by a Cu-CuxO-PbO mixture on the occurrence of the degradation mechanisms and the slag infiltration depth. It is observed that the direct-bonded refractory has a higher resistance against the infiltration of the Cu-CuxO-PbO mixture, whereas the fused grain refractory exhibits a higher resistance to chemical attack by the slag. The infiltration of the slag is more enhanced in the fused grain refractory by the higher infiltration depth of the Cu-CuxO mixture than in the case of the direct-bonded refractory. The presence of Cu-CuxO phase can cause chemical attack by the slag at higher depths in the refractory.status: publishe