Magnesium aluminate spinel inclusions are a concern in the steelmaking industry since these particles affect the processing and the properties of steel. During the refining of low carbon aluminum killed steel in the ladle furnace; the initial alumina inclusions shift their composition towards higher contents of MgO and eventually they become magnesium aluminate spinel inclusions. This research developed a kinetic model for the transformation of alumina inclusions to spinel in liquid steel. The aspects of simultaneous deoxidation and of solid state cation counterdiffusion were addressed in the model. Coupling the model for spinel inclusions to a kinetic model for the slag-steel reactions in the ladle furnace allowed verifying the modeled concentrations in the inclusions with the plant data measurements of ArcelorMittal Dofasco operations. Good agreement between the experimental and calculated Mg contents in the inclusions was obtained for most of the industrial heats analyzed. Finally, a sensitivity analysis of the coupled kinetic model was performed to compare the effect of the different processing conditions and mass transfer rates on the amount of Mg and spinel in the inclusions. Several results from this work indicate that the rate limiting step on the formation of magnesium aluminate spinel inclusions is the supply rate of dissolved [Mg] from the slag-steel reaction; the supply of [Mg] is in turn controlled by the changes at the slag-steel interface. / Thesis / Master of Applied Science (MASc)