Metallothermic Reduction of Natural Cassiterite

The process of phase formation during metallothermic reduction of tin and associated metals from natural cassiterite containing 74.4% SnO₂, 16.3% SiO₂, and 9.3% FeCO₃ is studied by methods of combined thermogravimetry and differential thermal analysis (or differential scanning calorimetry), as well as X­ray diffraction. Aluminum, calcium and calcium­aluminum master alloy (69.4 wt.% Ca) are tested as reducing agents. The possibility is demonstrated of extracting tin from cassiterite in the form of a metal and an alloy in agreement with predicted results of thermodynamic modeling with reducing agent stoichiometric consumption. It is found that reduction of cassiterite with aluminum proceeds actively in the range 1000–1150°C, and an increase in its consumption in excess of the stoichiometric requirement hardly affects the process temperature. When using a calcium­aluminum master alloy, tin from dioxide passes into the metal phase in two stages through formation of tin monoxide. Addition of aluminum to the calcium­aluminum master alloy or its replacement with a mixture of metallic calcium and aluminum slightly reduces the efficiency of the reduction process.