Stabilization of MgCr ₂O ₄ spinel in slags of the SiO ₂-CaO-MgO-Cr ₂O ₃ system

The objective of this study is to analyze the effect of MgO content and the slag basicity on the stability of the mineralogical species of the SiO ₂-CaO-MgO-Cr ₂O ₃ system. Slag samples were prepared in equilibrium at 1600°C under reducing conditions (pO ₂= 10 ^-9 atm). The MgO content ranged from 0 to 12 mass%, Cr ₂O ₃ was 10% and the slag basicity was held at 1 and 1.5. A thermodynamic analysis was carried out to estimate the most stable mineral phases in the slag. Experimental and calculated results show that Cr ₂O ₃ is mainly bound into MgCr ₂O ₄ spinel phase, even at low MgO content. SEM-EDS results show the evidence of three crystalline structures: (A) Octahedrons which correspond to MgCr ₂O ₄ spinel-type compound; (B) Elongated crystals which belong to calcium silicate compounds and (C) Massive grains that correspond to calcium silicates with impurites of Mg and Cr that did not crystallize completely.