Abstract
Refractory materials play a critical role in high temperature processes. During smelting, intrusions from the melt into the material and chemical reactions occur, thereby altering the composition of the refractory products. The refractory input materials and valuable metals can be recovered using different treatment processes. Consequently, the reuse of recycled products would reduce carbon emissions and conserve primary resources. However, due to the complex composition of the residual materials and the low quality of produced recycled products, the spent refractories currently end up in landfills. To address this problem, this study investigates alternative recycling processes to recover valuable metals as well as a clean refractory fraction from the spent refractories.
The focus of the investigations lies on spent magnesia chrome bricks from a shaft furnace. After a comprehensive characterization using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) as well as X-ray fluorescence analysis (XRF), different approaches for recovering the fractions of refractory material and valuable metals were evaluated. These include determination of magnetic properties, coarse grinding with subsequent sieve analysis, and leaching tests.
Characterization results indicate, that the greatest changes in the material occur on the hot side of the refractory brick facing the molten phase in the furnace. Therefore, this is the area where the highest concentrations of intruded phases and copper occur. These intrusions decrease towards the cold side, where no noticeable alterations can be detected. Depending on the origin of the spent refractory Copper can be present as Sulfide, Oxide or metal, aside of various compounds. The results of the sieve analysis show, that a coarse sieve cut after crushing would be useful to remove any adhering metal pieces. Furthermore, the susceptibility tests confirm that a ferromagnetic fraction can be separated. When treating the pre-concentrated material, a extraction of over 90 wt-% of copper in the leaching tests can be achieved. The results in overall show that recycling is possible using a combination of mechanical and hydrometallurgical process which, become more important in a world moving towards recycling, climate protection, and conservation of limited resources.