Corrosion mechanism of magnesia-chrome and alumina-chrome refractories in E-scrap smelting

Abstract

Pyrometallurgical processes have been widely recognised as the preferred technology for E-scrap recycling, and E-scrap smelting is usually accompanied by the formation of high-Al2O3-content slag. However, this slag can cause problems, such as refractory wear and even accelerated failure. Therefore, the corrosion mechanism of magnesia-chrome and alumina-chrome refractories in contact with FeOx-SiO2-CaO-Al2O3 smelting slag was experimentally studied in the range of 1300–1400 °C, in air (pO2 = 0.21 atm) and at pO2 = 10-7 atm. The results showed that refractory-component dissolution and new phases formation were the major causes of refractory degradation. The dissolution of the refractory components increased along with both increasing temperature and decreasing Al2O3 concentration in the initial slag. When decreasing the pO2, the dissolution of MgO and Al2O3 into the slag slowed down. New phases such as forsterite, anorthite, and spinel were detected at the interface between the slag and the bulk refractory. The formation of forsterite accelerated the refractory wear, whereas the newly formed (MgO,FeO)·(Cr2O3,Fe2O3,Al2O3) spinel phase acted as a protective layer against further corrosion. A lower Al2O3 concentration in the slag and a higher smelting temperature both densified the formed spinel layer. Additionally, a high oxygen partial pressure was beneficial to the formation of spinel in the magnesia-chrome refractory corrosion experiments. However, a low oxygen partial pressure was favourable for the formation of spinel on the surface of the alumina-chrome refractory materials. This study provides useful information for designing refractory materials and optimizing the processing parameters of E-scrap smelting.