4. Raw tin refining processes

Raw tin extracted from concentrates contains varying quantities of impurities such as Fe, Cu, Pb, As, Sb, Bi and S, which need to be eliminated to meet market requirements. A comparison between the probable ranges of grades encountered and the minimum specifications imposed by the London Metal Exchange provides a quantitative assessment of the objectives targeted by refining (table 4 ). In the case of crude tin from the reductive smelting of rich, clean alluvial concentrates (free of Pb, Cu, Bi and As), refining may be limited to iron removal, and involve only one stage: liquefaction 4.1.1