Abstract: Pre-enrichment on Kaldor slag which is rich in precious metals of Au，Ag，Pt，Pd，Se before it returns into Kaldo furnace for re-smelt can improve the working efficiency of the Kaldor furnace，reduce production cost，solve the problem of returned material accumulate.The pre-enrichment technology of Kaldor slag was studied by Tongling Nonferrous Metals Company，the results show that：With ferrous sulfate as the activator on sulfide minerals，sodium sulfide as the activator on oxide minerals，the flotation flowsheet of two roughing two cleaning two scavenging and middlings return in order，final concentrate with grade of Au，Ag，Pt，Pd，Se is 508.76 g/t，55.78%，9.36 g/t，16.92 g/t，2.94%，and recovery rate of Au，Ag，Pt，Pd，Se is 95.60%，90.09%，78.00%，88.50%，86.70%;Using SLon-400 type centrifugal separator on flotation tailings，concentrate grade of Au，Ag is 9.45 g/t and 1 600.00 g/t，recovery rate of Au，Ag is 2.27% and 3.28%，flotation-gravity separation total recovery rate of Au，Ag is 97.87% and 93.37%.Therefore，flotation-gravity separation is an efficient recovery process for Kaldor furnace slag，gold and silver in the gravity separation tailings can be recovered by chemical dressing method.

Key words: Kaldo slag, Flotation, Preconcentration, PAC, Centrifuge separator