Thermodynamics of the metallic phase growth during the solid phase reduction of metals in complex oxides

To improve the technologies of solid-phase reduction of metals in ores, it is necessary to study in detail the regularities of the growth of nuclei of the metal phase, taking into account the conditions existing in the reduction aggregates. At the first stage of the study, the general regularities of the growth of a new phase in a multicomponent oxide system were studied. Using the methods of non-equilibrium thermodynamics, a complex physicochemical description of the solid-phase reduction of metals in a multicomponent oxide phase was obtained, taking into account the thermal and diffusion processes occurring in this case. Additionally, using the methods of chemistry of imperfect crystals, the regularities of the influence of the movement of anionic vacancies on the thermodynamic state of the system were formulated. For the considered system the physicochemical equations for the balance of vacancies and entropy were written. The developed new theory made it possible to consider thermal and diffusion processes, as well as the processes of vacancy movement in a multicomponent oxide system in their complexity. For a practical study of the reduction of metals in ores, the case of the growth of a metal particle from the initial phase of the ore was considered, taking into account the additional effect of the reducing agent on the process. On the basis of an integrated approach, a general expression for the production of entropy in the system of a growing metal nucleus, an initial ore phase and a phase of reducer inclusions was obtained. The carried out research made it possible to develop a mathematical model of the growth of a metal crystal in the volume of the oxide phase, depending on the heating mode and the composition of complex oxides. In particular, the developed mathematical model made it possible to calculate the growth rate of the metal nucleus in the initial multicomponent oxide phase. The obtained technique also made it possible to evaluate the degree of influence of the movement of anionic vacancies on the regularities of the reduction process.