<p>This study systematically explored the role of coordination cations in both tetrahedral and octahedral sites, in the formation of chromium-bearing spinel for the detoxification of CaO–SiO₂–MgO–MnO–Al₂O₃–Cr₂O₃ stainless steel slags. A comprehensive characterization was adopted, combining FTIR, Raman, XRD, and EPMA analyses. The structural and compositional evolution of spinel and coexisting liquid phases was elucidated, quantifying the degree of polymerization (DOP) and clarifying the influence of MnO/MgO and Cr₂O₃/Al₂O₃ mass ratios on the silicate network. Experimental and thermodynamic results consistently revealed that increasing MnO/MgO and Cr₂O₃/Al₂O₃ mass ratios had a synergistic effect, promoting the formation of (Mg,Mn)(Al,Cr)₂O₄ spinel and the incorporation of Cr elements. The partitioning behavior of cations between spinel and liquid phases was systematically analyzed across compositionally varied slags during detoxification, with particular focus on their coordination on the formation of spinel. Moreover, the interfacial behavior between the spinel precipitated from hot stainless steel slags and the liquid phases was also explored. Those indicated the potential of spinel phase formation could be enhanced by adjusting the types and concentrations of coordination cations. This study thus provides novel fundamental insights for hot industrial slags detoxification and the further resource recovery process.</p>