The flashFlash converter at Rio Tinto KennecottRio Tinto Kennecott in Salt Lake City, Utah, has been operating with a calcium ferrite (Ca2Fe2O5) slagSlag since its commissioning in 1995. Major components of the slagSlag system are Ca, Fe, and Cu oxides, but the minor components silicaSilica and arsenicArsenic significantly affect the slagSlag and furnaceFurnace operationOperation. Lime (CaO) fluxingFluxing practice originally aimed to flux only ironIron in the furnaceFurnace feed. Issues controlling solid buildup in the converting furnaceFurnace eventually drove a better understanding of the impact of minor components on the slagSlag system. An empirical equation was developed between magnetic susceptibility of the slagSlag and its major and minor components. This understanding allowed a controlled variable (lime flux to the furnaceFurnace) to vary with uncontrolled variables (major and minor components in slagSlag) aiming to maintain a constant magnetic susceptibility of the slagSlag, which is desirable for maintaining a controlled amount of accretionAccretion in the furnaceFurnace, improving campaign life and operability. New thermodynamicThermodynamics understanding provided by collaboration with researchers at the UniversityUniversities of Queensland facilitated a recent modification of the fluxingFluxing strategy, based on thermodynamicThermodynamics fundamentals, to better control furnaceFurnace accretionAccretion.