The EAF and LF slag processing became an actual issue at the present day metallurgy. The possibility of joint and complete utilization of both electric furnace and ladle slag is considered in this paper. The purpose of the work was to develop a method for joint processing of EAF and LF slag with the production of marketable products. A simplex-lattice planning method was used during the work. The raw mixture consisted from EAF slag, ladle slag and limestone. The components of the raw mixture were mixed according to the experimental design, heated and melted under reducing conditions. The phase and chemical composition of melting products, obtained during the experiment, were determined. The results of the experiment showed that both slags and lime can be used together to produce Portland clinker and pig iron. These products are in good agreement with normative documents and thus, they can be used in further production.