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How does the Parkes process remove silver and gold from lead bullion?
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lead processing
A zinc-lead blast furnace and lead-splash condenser. This technology is utilized mainly for producing zinc while managing both lead and zinc from raw materials, a technique that was highly influential in 20th-century smelting.
The Parkes zinc-desilvering process is a pyrometallurgical method used to extract silver and gold from lead bullion.21
The process functions through the following steps:
- Addition of Zinc: Small quantities of zinc (less than 1 percent by weight) are added to the molten lead bullion.2
- Reaction: When the mixture is stirred, the zinc reacts to form compounds with the gold and silver, as these precious metals are more soluble in zinc than in lead.21
- Separation: Because these zinc-precious metal compounds are lighter than the molten lead, they rise to the surface as the mixture cools to below 370 °C (700 °F).2
- Removal: The resulting crust is skimmed off the top of the lead and sent to a parting plant for the recovery of the silver and gold.321
After the precious metals are removed, the remaining zinc is typically extracted from the lead by reheating the metal and using a vacuum to vaporize and collect the zinc for reuse.2