How does silver electrorefining purify silver?

Silver electrorefining is a process used to achieve high-purity silver, typically reaching 99.9% (three-nines fine) or even 99.99% purity. The process begins by casting impure silver bullion, often referred to as doré, into anodes.12

These anodes are placed into an electrolytic cell containing a solution of silver-copper nitrate. When an electric current is applied, the silver in the anode dissolves into the electrolyte and subsequently deposits onto the cathodes.12

Two primary techniques are used for this electrolytic process:
* Moebius system: The electrodes are positioned vertically.1
* Thum Balbach system: The electrodes are positioned horizontally.1

During this process, impurities such as gold and platinum-group metals do not dissolve; instead, they collect as slimes at the bottom of the refining tank. These residues are later recovered and treated through further parting or affination processes to separate and refine the remaining precious metals.123