What happens during slag fuming in the treatment of zinc-processing residues?

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In the context of silver processing, slag fuming is a method used to treat residues remaining after zinc concentrates have been roasted and leached.

During this process, the residue is melted to form a slag. Powdered coal or coke is then blown through the molten slag along with air. This triggers two primary chemical transformations:

Zinc Recovery: The zinc contained within the residue is reduced to its metallic form and vaporized, allowing it to be recovered from the slag.
Silver and Gold Collection: The lead present in the residue is converted into metallic form. As it forms, this lead acts as a solvent, dissolving the silver and gold.

The resulting lead bullion, which contains the precious metals, is collected periodically and subsequently sent for lead refining.1