Steel is an indispensable material used in manifold industries, like construction, transportation or engineering. The global steel production is steadily rising and reached a new record with 1.869 million tons in the year 2019. More than 70% of the worldwide steel production is based on the blast furnace – basic oxygen furnace process route, whereof the steelmaking technique using the basic oxygen furnace converter has been developed in great parts in cooperation of the University of Leoben and the Austrian-based steel producer voestalpine Stahl GmbH. During this treatment method high amounts of basic oxygen furnace slag are generated, which consist of valuable elements like iron, phosphorus, chromium or manganese in addition to the calcium and silicon oxides. In Austria, regulations regarding the chromium amount in this slag system allow only limited use of basic oxygen furnace slags. To increase the recovery of this residual product and to access the containing valuable elements, a novel treatment approach called InduRed was developed at the Chair of Thermal Processing Technology at the University of Leoben in cooperation with the companies voestalpine Stahl GmbH and SCHOLZ Austria GmbH. By using this treatment method, an inductively heated plant called InduMelt was built and its specific characteristics during operation have been analyzed. By reducing the input slag mixture with carbon powder, this treatment method separates the phosphorus from the initial slag mixture via a gas phase and produces an iron-rich alloy and an additional product slag mixture. The gaseous phosphorus therefore can possibly be used as an input stream in the fertilizer production industry and the emerging liquid iron alloy has a potential to be used again as a recycled steel product. Previous research regarding the efficient integration of the InduRed plant into the industrial steelmaking process state that, during a novel process sequence, especially a chromium- and manganese-rich slag system can be produced, which can potentially be treated in the InduRed plant. By reducing this novel slag, low phosphorus gasification degrees were identified resulting in a low efficiency of this treatment method compared to treating slags, which contain only low amounts of manganese and chromium. In this master’s thesis the influence of both chromium and manganese on the phosphorus reduction degree and the phosphorus activity in the occurring liquid metal phase is analyzed by conducting simulations using the thermochemical simulation software FactSageTM. By analyzing the temperature influence, the basicity and the amounts of chromium and manganese of the input slag mixture, optimizations of the carbo-thermal treatment of this initial slag system were derived. Especially a strong dependency of the maximum treatment temperature and the input amounts of chromium and manganese on the phosphorus distribution between the emerging metal and gas phase is identified. Further benchmarks with results from other researchers underline the findings and trends, which are generated based on the conducted simulations.