PROCESS FOR REFINING SILVER BULLION WITH GOLD SEPARATION

摘要

The present invention concerns a process for refining silver bullion, i.e. raw silver containing generally more than 90 % silver besides Se, Pb, Au, Cu and platinum group metals (PGM) as main impurities. The process comprises the steps of: optionally removing Se as gaseous SeO2 from the molten metallic phase by injecting air, which is preferably O2 enriched, into the metallic phase at a preferred bath temperature of 1000-1100 °C; optionally slagging off the Pb by contacting the molten metallic phase with a silica and borax based flux at a preferred bath temperature of 1000-1150 °C; granulating the molten metallic phase in water, thereby forming Ag rich granules; leaching the Ag rich granules with HNO3 at a temperature above 50 °C, preferably in an O2 enriched atmosphere, followed by filtration, thereby separating an Au bearing residue from an Ag rich liquor; heating the Ag rich liquor, thereby evaporating H2O and forming an AgNO3 bearing melt; maintaining the AgNO3 bearing melt at a temperature of 220-350 °C for at least 15 minutes, thereby forming a mixture of a purified AgNO3 and of a denitration residue containing essentially all the PGM as oxides; separating the purified AgNO3 from the denitration residue. By this process, the many drawbacks of the classical electrolytic refining of silver are avoided.