To separate tin and lead from lead slag consisting essentially of the tin and the lead by obtaining a leaching of dust produced in a converter, in a copper smelting process.

The lead slag consisting essentially of lead sulfate and stannic oxide, is reacted with aq. solution containing carbonate, such as sodium carbonate to change the lead sulfate into lead carbonate. The lead carbonate in the lead slag after the above reaction is desirably leached with nitric acid, and thereby, the leaching solution selectively dissolving the load and stannic oxide as insoluble residue are separated. The lead is separated as the deposit of refractory compound and recovered from the above leached solution selectively dossolving the lead with desirably sufuric acid.