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Why is molten lead used to condense zinc vapor in a zinc-lead blast furnace?

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sphalerite — zinc processing Sphalerite from Baxter Springs, Kansas.

In a zinc-lead blast furnace, molten lead is used to condense zinc vapor because it facilitates a process known as shock-chilling.12

When zinc is reduced from its ore, it exists as a vapor mixed with gases like carbon dioxide, which can cause the zinc to re-oxidize if cooled slowly. To prevent this, the gas stream is directed into a lead-splash condenser, where an intense shower of molten lead droplets is created by revolving rotors.1

The zinc vapor is rapidly absorbed into the molten lead, effectively "shock-chilling" the gas and preventing the reverse reaction with carbon dioxide. Once the zinc-enriched lead is withdrawn and cooled, the saturation point of the zinc is reached, allowing the molten zinc to separate as a distinct layer on the surface for collection. The remaining lead is then returned to the condenser to continue the cycle.12