THERMODYNAMIC SIMULATION AND LABORATORY-SCALE EXPERIMENTS OF TIN SMELTING AT AL2O3 SATURATION

• Main Author: Nur Iksan, Afif
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/85218
• Institution: Institut Teknologi Bandung

The global demand for tin is projected to continue its upward trajectory, driven by its wide range of applications across various industrial sectors, from minor components to crucial elements that are essential for the advancement of modern technologies. In Indonesia, established tin smelting technologies currently in use include the reverberatory furnace and the top submerged lance (TSL) furnace. A significant issue encountered in tin smelting operations is the corrosion of refractory materials that comes into direct contact with the molten slag. Magnesiabased refractories are commonly used. Magnesia-based refractories offer several advantages, including excellent mechanical properties and durability at high temperatures, good thermal efficiency, resistance to basic slag attacks, and lower costs compared to alumina-based refractories. However, these refractories have limitations in acidic slag environments and exhibit high thermal expansion, which can lead to the formation of gaps and cracks, thereby degrading the refractory lining. Otherwise, alumina-based refractories emerge as a promising alternative, particularly when dealing with the unpredictable slag compositions, owing to alumina's amphoteric characteristics. Nevertheless, prolonged interaction with aggressive slag can lead to substantial degradation of the refractory material. Therefore, this study aims to evaluate the feasibility of employing alumina refractories in tin smelting processes. A series of thermodynamic simulations and laboratory-scale experiments were conducted. The FactSage 8.2 software was employed to simulate the solubility of Al2O3 in slag and the ratio of %Sn in slag to %Sn in metal (L) during the smelting and reduction stages in the TSL furnace technology. The parameters examined included Fe/SiO2 (0.3 – 1.6), CaO/SiO2 (0.3 – 1.6), %Sn in slag (3 – 20%), and temperature (1100 – 1600°C). Subsequently, laboratory-scale experiments were carried out to validate the simulation results. 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 hours. The experimental parameters varied included Fe/SiO2 (0.3 – 1.6), CaO/SiO2 (0.3 – 1.6), and %Sn in slag (3 – 20%). The resulting smelting samples were analyzed using Scanning Electron Microscope – Energy Dispersive Spectroscopy (SEM-EDS) to determine the solubility of Al2O3 in the slag, the ratio of %Sn in slag to %Sn in metal, and the potential phases formed during high-temperature smelting. The simulation results revealed that the solubility of Al2O3 during the smelting and reduction stages is significantly influenced by temperature, Fe/SiO2, and CaO/SiO2, whereas the ratio of %Sn in slag to %Sn in metal (L) appears to be independent of these variables, being primarily influenced by the %Sn in the slag. Experimental results at 1300°C with varying Fe/SiO2 ratios in the range of 0.3 to 1.6, lower Fe/SiO2 ratio leads to an increase in Al2O3 solubility in the slag, accompanied by the formation of anorthite (CaAl2Si2O8). In contrast, a higher Fe/SiO2 ratio results in a decrease in Al2O3 solubility, accompanied by the formation of spinel (FeAl2O4). A similar trend occurs in experiments varying the CaO/SiO2 ratio within the same range. Initially, Al2O3 solubility increases, accompanied by the formation of spinel (FeAl2O4). Subsequently, as the CaO/SiO2 ratio increases, Al2O3 solubility decreases, and a new solid phase, melilite ((Ca,Na)2(Al,Mg,Fe2+)(Si,Al)2O7), forms. These solid phases can form within the slag matrix or at the slag-crucible interface. The formation of solid phases at the slag-crucible interface is effective in preventing further penetration of molten slag into the crucible lining, as a protective layer composed of solid phases generated through slag-crucible interactions during high-temperature smelting processes. Moreover, under constant CaO/SiO2 and Fe/SiO2 ratios of 0.3, reducing the %Sn within the slag was found to increase the solubility of Al2O3, due to the creation of a more aggressive slag towards Al2O3 crucibles.