Why is alumina added in the Magnetherm process?

In the Magnetherm process, alumina (aluminum oxide, Al₂O₃) is added to the charge to lower the melting point of the dicalcium silicate slag produced during thermal reduction.1

While dicalcium silicate typically has a high melting point of approximately 2,000 °C (3,600 °F), which keeps it in a solid state, the addition of alumina reduces this melting point to a range of 1,550–1,600 °C (2,825–2,900 °F). This allows the slag to remain liquid, enabling it to be heated directly by electric current through a water-cooled copper electrode.1