Thermodynamic Simulation and Laboratory-Scale Experiments of Tin Smelting at Al₂O₃ Saturation

A significant issue encountered in smelting operations is the corrosion of refractory materials that come into direct contact with the molten slag. Magnesia-based refractories are commonly used in nonferrous smelting operations. On the other hand, alumina-based refractories emerge as a possible alternative, particularly when dealing with the unpredictable slag compositions, owing to alumina's amphoteric characteristic. Nevertheless, prolonged interaction with aggressive slag can lead to substantial degradation of the refractory material. The research on the use of alumina-based refractories in tin smelting is not well known. Hence, this paper focuses on slag-refractory interaction in the tin smelting process at Al₂O₃ saturation. A series of thermodynamic simulations and laboratory-scale experiments were conducted. The software FactSage 8.2 was employed to simulate the solubility of Al₂O₃ in slag and the ratio of Sn content in slag to Sn content in metal under the conditions relevant to tin concentrate smelting and tin slag reduction stages. The experiments utilized synthetic slag composed of SnO-FeO -CaO-SiO₂-Al₂O₃, conducted in a vertical tube furnace at a temperature of 1300 °C for 2 h. The experimental parameters that were varied were the Fe/SiO₂ ratio in slag (0.3-1.6), CaO/SiO₂ ratio in slag (0.3-1.6), and Sn content in slag (3-20%). The simulation results revealed that the solubility of Al₂O₃ during the tin concentrate smelting and tin slag reduction stages was significantly influenced by temperature, Fe/SiO₂, and CaO/SiO₂, whereas the ratio of the Sn content in slag to the Sn content in the metal appeared to be independent of these variables, being primarily influenced by the oxidation condition. Experimental results at 1300 °C showed that varying Fe/SiO₂ within the range of 0.3-1.6 led to an initial increase in Al₂O₃ solubility in slag at lower Fe/SiO₂ ratios, followed by a decrease in Al₂O₃ solubility in slag at higher Fe/SiO₂ ratios. A similar trend was observed with variations in CaO/SiO₂ within the same range, accompanied by the formation of new solid phases, such as hercynite spinel at lower CaO/SiO₂ ratios and melilite at higher CaO/SiO₂ ratios. Moreover, under constant CaO/SiO₂ and Fe/SiO₂ ratios of 0.3, reducing the Sn content in the slag was found to increase the solubility of Al₂O₃ due to the creation of a more aggressive slag toward Al₂O₃ solid.