Tin Production
Tin Production
0.01% Tin in placers and 0.1% in ores make the processing commercially useful; usually several percents of tin in ores are satellites of tungsten, zirconium, caesium, rubidium, rare-earth elements tantalum, niobium and other commercially valuable elements. Fresh raw materials are enriched: placers gravitationally, ores - by flotation only or gravity flotation. Concentrates with 50-70% tin are roasted for sulphur removing and treated by HCl for getting rid of iron. Such impurities as volframite (manganese tungstate (Fe, Mn) WO4) and scheelite CaWO4 are treated by HCl; then WO3xH2O is separated by NH4OH. Pig tin (94-98% Sn), which contains Copper, Lead, Iron, Arsenic, Antimony, Bismuth, is extracted by fusion with carbon in electrical or flame furnaces. On furnace outlet the pig tin is filtered at 500-600°C through coke or centrifuge for iron separation. The rest of iron and copper are removed by mixing molten metal with sulphur; solid sulphides of impurities float up, and are removed from the surface. Refining from arsenic and antimony are processed by the same method mixing with aluminium, and lead is removed by SnCl2. Sometimes Bismuth and Lead evaporate in vacuum. Electrolytic refining and floating-zone refining are used relatively seldom for obtaining high-pure tin.