What is the purpose of calcium fluoride or calcium oxide flux in ferrovanadium production?

In the production of ferrovanadium, calcium fluoride or calcium oxide is added to the reaction mixture as a flux. The primary purpose of this substance is to promote fluidity and facilitate the removal of impurities by forming a slag during the aluminothermic process.12

Specifically, when a mixture of vanadium pentoxide ($V_2{O}_5$), aluminum, and the flux is heated in an electric-arc furnace, the aluminum reduces the vanadium pentoxide to vanadium metal, which then dissolves into the molten iron. Simultaneously, the aluminum is converted into alumina ($A{l}_2{O}_3$), which combines with the flux to form a slag that can be separated from the metal.1