Experimental studies and thermodynamic modeling of metal-slag-refractory interactions in non-ferrous pyrometallurgical processes

In the non-ferrous pyrometallurgical processes, such as Cu/Ni making processes, the liquid phases, such as Ni alloys, matte, and slag phases exhibit complex behavior. Moreover, refractory lining materials generally react with the liquid phases, such as slag phases under extreme conditions at high temperatures in the Cu/Ni smelting and converting furnaces. Therefore, various solid and liquid solutions can be formed, and the fayalite FeOx-SiO2 slags including CaO, MgO, ZnO, and impurities can penetrate and corrode the lining refractory materials of the furnace, such as MgO-Cr2O3, MgO-Al2O3, and/or MgO-C. In order to increase efficiency of Cu/Ni processes and save costs, it is needed to understand and predict the complex behavior of liquid phases and the corrosion behavior of refractory materials against liquid slags. Thermodynamic modeling can be used to understand the behavior of liquid phases and refractory corrosion against slag phases using thermochemical software, such as FactSage. The thermodynamic modeling is used to calculate phase equilibria based on Gibbs free energy minimization methodology. The Gibbs free energy of non-ideal solution phases can be expressed mathematically by several thermodynamic models, such as Bragg-Williams random mixing model and Modified Quasichemical Model. The parameters of models can be optimized using the Calphad methodology in order to fit calculated phase equilibria and thermodynamic properties with experimentally determined data. The thermodynamic calculations based on the optimized parameters can be used to interpret and predict the behavior of liquid phases and slag-refractory reactions. In this doctoral thesis, the parameters of the ternary Ni-Co-C, CaO-MgO-ZnO, and MgO-ZnO-SiO2 systems were optimized using FactSage based on own experimental phase equilibria studies, as well as data from the scientific literature. The Bragg-Williams model was used for solid solutions, while the modified quasi-chemical model was used for the liquid solutions. All the optimized systems agreed well with the phase equilibria studies within the error limits of the experimental data. Moreover, the corrosion behavior of refractory materials against liquid slag was studied and interpreted using FactSage. Interfacial reactions between MgO-Cr2O3, MgO-Al2O3, and MgO-C refractories and CaO-FeOx-SiO2 slags were studied with experimental work, such as sessile drop and immersion tests. The experimental results also showed good agreement with thermodynamic calculations using FactSage. With the new thermodynamic databases developed in this work, pyrometallurgical processes can be optimized further in the future, taking into account metal-slag-refractory interactions.