| 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.
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