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How can silver be recovered from copper-refining slimes?

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Molten copper pours from a large industrial furnace into rectangular molds at a copper smelting facility, with glowing metal and industrial equipment visible. — copper processing Molten copper being made into plates.

Silver is recovered from copper-refining slimes through a multi-step metallurgical process designed to isolate precious metals from base metal impurities.1

Smelting to Doré

During the electrolytic refining of copper, insoluble impurities known as slimes accumulate at the bottom of the refining tanks. These slimes are collected and smelted in a furnace to oxidize and remove virtually all base metals, leaving behind a metallic mixture called doré. This product typically consists of silver, gold, and platinum-group metals.1

Electrolytic Refining

The doré is cast into anodes and subjected to electrolysis in a silver-copper nitrate solution to separate the silver. Two primary systems are used for this process:1
* Moebius system: Electrodes are arranged vertically.1
* Thum Balbach system: Electrodes are arranged horizontally.1

Through these electrolytic techniques, silver is dissolved into the electrolyte and deposited onto cathodes, typically achieving a purity of 99.9 percent or higher.1