Oxide Dissolution Losses of Copper, Lead and Tin in Slags

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In copper, lead or tin smelting, gangue minerals and impurities are concentrated into slag phase and valuable metals are recovered as molten state. Some amount of valuable metal losses to slag as dissolution and suspension in the smelting step. It is very important to minimize the valuable metal loss to slag in the smelting. To clarify effects of slag composition, oxygen potential and temperature on valuable metal loss, equilibrium experiments between these metals and FeO-CaO-SiO_2 slags were carried out at the temperature of 1200 to 1300ﾟC. The experimental results are summarized as follows.1. Copper in slag was mono-valent and lead and tin in slag were di-valent. The dependence of metal solubility in slag related to its valency.2. The contents of copper and tin were similar for both binary fayalite (FeO_x-SiO_2) and ferrite (FeO_x-CaO) slag, and much higher than those in ternary FeO_x-CaO-SiO_2 slag. The minimum solubilities of copper and tin were observed in the ternary FeO_x-CaO-SiO_2 slag whose composition were close to saturation with solid di-calcium silicate and 25% iron oxide. The slag composition of the ternary FeO_x-CaO-SiO_22 forms a stable slag solution by neutralization of acidic SiO_2 with basic CaO.3. Big solubility of lead whose oxide had a big affinity with SiO_2 was observed in fayalite slag with big activity of SiO_2. Ferrite slag free from SiO_2 was effective to reduce oxide lead loss in slag. When slag contains SiO_2 inevitably, neutralization of SiO_2 with CaO reduces lead loss in slag.