Alternative Cr-free refractory materials are still sought to substitute magnesia-chrome refractories, as the latter negatively influences environment and labor conditions due to the release of carcinogenic Cr6+ compounds.

Spinel (MgAl2O4), hercynite (FeAl2O4) and galaxite (MnAl2O4) successfully substituted picrochromite (MgCr2O4) in magnesia-chrome refractories in burning zones in cement rotary kilns. In this work, we propose a new multicomponent spinel (Mg,Zn)[Fe,Al]2O4 as a matrix or aggregate used in magnesia-based refractories for high-temperature furnaces in the copper industry. Besides the thermomechanical advantage of using spinel in the composition of the refractory via microcrack formation, which dissipates energy, spinel may accept multiple ions from slag like Fe2+/3+, Zn2+, Cu2+, which are deleterious for refractory materials. Pre-saturation of the refractory spinel matrix with slag elements may hinder the further dissolution of the refractory by reducing the concentration gradient of elements between slag and refractory, thus lowering the driving force (chemical potential) for diffusion-induced corrosion, as well as the formation of a protective layer at slag/refractory interface.

This work presents the production route of new Cr-free aggregate from the system (Mg-Zn-Fe-Al-O) with different compositions. We reveal the phase composition (XRD), iron valency and site occupancy (Mosbauer spectroscopy), microstructure (SEM/EDS), physical properties, penetration depth by copper slag, variation of slag contact angle with temperature, and sintering characteristics by dilatometry.
This work relates to the European patent submission no: EP24153408.0 (Inventor: I. Jastrzębska).