Investigating the Compositional Space of Gas-Phase Synthesized Fayalitic Model Slags Aiming at Cobalt Recovery

Metallurgical waste streams contain minor yet significant contents of valuable and scarce elements which are commonly lost due to their low concentrations. The necessity of developing efficient recycling methods of these chemically diverse material systems is constantly gaining both public and technological attention since resource demands of high-technology elements are expected to rise drastically in the future. A novel approach to recover diluted elements from slags is the concept of Engineered Artificial Minerals (EnAM) which aims at entrapping target elements in separable crystalline phases. In this study, slag synthesis through flame spray pyrolysis (FSP) and characterization experiments are combined with theoretical density functional theory (DFT) calculations to identify potential EnAM for Co recovery. Upon validating the viability of stoichiometric slag synthesis and the DFT framework, it is shown that the actual occurrence of flame-synthesized phases can be predicted considering their computed enthalpy of formation. The thus-defined compositional space, which is spanned by potentially forming slag compounds, is employed to identify promising additives for EnAM formation. Systematic analysis of the additive effect on crystallization revealed that Co crystallizes in a Fe–Mg-Co–O cubic spinel, making this phase a good EnAM candidate.

Graphical Abstract